1

MICHAEL OKONKWO C.

PG/M. Sc/09/51723

THE EFFECT OF 4-ACYL SUBSTITUENTS ON THE INFRARED STRETCHING

FREQUENCIES OF SOME 1-PHENYL -3- METHYL -4- ACYLPYRAZOL -5-ONES

AND THEIR MAGNESIUM (II) ,COBALT(II), COPPER (II) AND ZINC (II)

CHELATES.

PURE AND INDUSTRIAL CHEMISTRY

A THESIS SUBMITTED TO THE DEPARTMENT OF PURE AND INDUSTRIAL

CHEMISTRY, FACULTY OF SOCIAL SCIENCES, UNIVERSITY OF NIGERIA, NSUKKA

Webmaster

Digitally Signed by Webmaster’s Name

DN : CN = Webmaster’s name O= University of Nigeria, Nsukka

OU = Innovation Centre

MARCH, 2011

2

THE EFFECT OF 4-ACYL SUBSTITUENTS ON THE INFRARED STRETCHING FREQUENCIES OF SOME 1-

PHENYL -3- METHYL -4- ACYLPYRAZOL -5-ONES AND THEIR MAGNESIUM (II) ,COBALT(II), COPPER (II) AND

ZINC (II) CHELATES.

BY

OKPAREKE OBINNA CHIBUEZE

PG/MSC/06/42054

DEPARTMENT OF PURE AND INDUSUTRIAL CHEMISTRY

UNIVERSITY OF NIGERIA, NSUKKA

MARCH 2011

3

TITLE PAGE

THE EFFECT OF 4-ACYL SUBSTITUENTS ON THE

INFRARED STRETCHING FREQUENCIES OF SOME 1-

PHENYL -3- METHYL -4- ACYLPYRAZOL -5-ONES AND

THEIR MAGNESIUM (II) ,COBALT(II), COPPER (II) AND

ZINC (II) CHELATES.

BY

OKPAREKE OBINNA CHIBUEZE

PG/MSC/06/42054

BEING A RESEARCH PROJECT SUBMITTED TO THE DEPARTMENT OF

PURE AND INDUSUTRIAL CHEMISTRY, UNIVERSITY OF NIGERIA,

NSUKKA IN PARTIAL FUFILLMENT FOR THE AWARD OF MASTER OF

SCIENCE DEGREE IN PHYSICAL CHEMISTRY

4

CERTIFICATION

I hereby certify that Okpareke Obinna Chibueze , a postgraduate

student in the department of pure and industrial chemistry with

registration number PG/MSc/06/42054 has satisfactorily

completed the requirements for course and research work for the

award of a degree of masters in physical chemistry, The work

embodied in the research work is original and has not been

submitted in part or full for the award of any other diploma or

degree in this or any other university.

Prof. E. C Okafor Dr P.O Ukoha

Supervisor Head of Department.

5

ACKNOLEDGEMENT

Iam immensely grateful to my supervisor Prof E.C Okafor for his fatherly guidance and

assistance during the course of this work. I also wish to express my profound gratitude to

Dr C.O.B Okoye and the department of Pure and Industrial chemistry for giving me

graduate assistanship at a time this research work was almost coming to a halt. My

appreciation and gratitude also goes to Mr J.N Asegbeloyin for his immeasurable

assistance during the course of this work,Dr P.O Ukoha for always listening and

providing advice whenever I came calling with my research problems, Mr F.O Ukoha of

S.E.D.I Enugu ,J.I Ugwu; E.I Mborji,and S.I Odoh for their technical assistance.

I also express my gratitude to my colleagues and friends ,Mrs Ijeoma, Chizoba,Toluhi,

Mrs Ibekwe ,Felix ,Solo Okereke,Atiga, Helen, Mr Ujah,Mr Ayuk, Iyke Odoh and

Chijioke olelewe for their encouragement and support. My gratitude also to my uncle

Architect Chidi Onwuka for his financial and moral support during this work and Mr T,O

Ujam of the University of Waikato Newzealand for his assistance in carrying out the

analysis, To my parents Mr and Mrs S.N Okpareke and my siblings for their support and

understanding and finally to God Almighty for his infinite mercy.

6

DEDICATION

To a very special friend, Evelyn Fuludu for urging me on.

7

ABSTRACT

The divalent metal chelates of Mg,Co,Cu and Zn with 4-acetyl (hpmap), 4-

benzoyl(hpmbp),4-butyryl(hpmbup),4-capyroyl(hpmcp),4-propiony

(hpmprp) and 4-palmitoyl(hpmpp) derivatives of 1-phenyl -3-methyl

pyrazol-5-one have been synthesized and characterized by UV ,IR, and

conductivity measurements. It is shown that the ligands behaved like

bidentate enols, all forming neutral chelates with the metal ions , bonding

through oxygen of the enolic hydroxyl group and /or the oxygen atom of

the carbonyl group of the ligands keto-enol tautomer. The i.r spectra of the

ligands and their chelates have been measured between 4000cm-1

and

400cm-1

and assignments proposed for observed frequencies. The effect of 4-

acyl substituents on the carbonyl stretching frequencies of the complexes

was also investigated and the results showed that there was an increase in the

carbonyl stretching frequency bands as the length of the alkyl substituent

increased for magnesium (II),cobalt(II) and copper (II) chelates and the

reverse trend was observed for zinc (II) chelates.The infrared carbonyl and

metal oxygen stretching frequencies of the transition metal chelates were

also compared with the Irving and Williams stability order for transition

metal complexes(Cu > Ni >Co >Mn >Zn) and it was observed that the

magnitude of the M-O stretching frequencies followed closely the Irving

Williams stability order while the C=O stretching frequencies did not. This

+has been attributed to electronic and steric effects.

8

TABLE OF CONTENTS

Title page …………………………………………………………………………….. ii

Certification …………………………………………………………………….. iii

Acknowledgement ……………………………………………………………….. iv

Dedication …………………………………………………………………. v

Abstract ……………………………………………………………………… vi

List of figures ……………………………………………………………… xi

List of tables ……………………………………………………………………. xiii

Abbreviations ………………………………………………………………… xiv

CHAPTER ONE

1.0 Introduction ……………………………………………………… 1

CHAPTER TWO

2.0 Literature review ……………………………………………………………… 4

2.10 Concept of Chelation ………………………………………………………….. 4

2.11 Metal chelate complexes …………………………………………………………. 5

2.12 Ion –pair complexes …………………………………………………………….. 5

2.13 Additive complexes ……………………………………………………………….. 5

9

2.20 Chelation with β-diketones ……………………………………………………… 6

2.30 Chelation with 4-acylpyrazolones ………………………………………………… 8

2.40 Stability of metal chelates ………………………………………………….... 10

2.41 Nature of the chelating agent …………………………………………………..10

2.42 The size of the chelate ring ……………………………………………… 11

2.43 The nature of the central metal …………………………………………….. 11

2.44 The nature of the metal-ligand bond ……………………………………….. 11

2.50 Previous work done with β-diketones …………………………………… 12

2.51 Physical properties and structure elucidation ……………………………… 13

2.52 Isolation and spectroscopic studies …………………………………………. 15

2.60 Previous work on metal chelates of β-diketones ………………………………..17

2.61 The chemistry of magnesium …………………………………………………...17

2.62 Review of previous work done on magnesium chelates of β-diketones ………..19

2.70 Chemistry of cobalt ………………………………………………………19

2.71 Review of previous work done on cobalt chelates of β-diketones …………….23

2.80 The chemistry of copper ………………………………………………………..24

2.81 Previous work done on copper chelates of β-diketones …………………………26

2.90 The chemistry of zinc …………………………………………………………… 28

2.91 Previous work done on zinc chelates of β-diketones ……………………………...29

10

2.92 Spectroscopic techniques used in the study of ligands and metal complexes …… 30

2.93 Ultraviolet spectroscopy ……………………………………………………… 30

2.94 Infrared spectroscopy ………………………………………………………… 31

CHAPTER THREE

3.0 Experimental …………………………………………………………. 33

3.1 Laboratory apparatus and equipments ……………………………………….. 33

3.2 Laboratory reagents ……………………………………………………………. 33

3.3 Synthesis of 1-phenyl-3-methyl-4-acylpyrazol-5-ones …………………………35

3.31 Synthesis of 1-phenyl-3-methyl-4-acetylpyrazol-5-ones (HPMAP) …………… 35

3.32 Synthesis of 1-phenyl-3-methyl-4-benzoylpyrazol-5-ones (HPMBP) …………… 35

3.33 Synthesis of 1-phenyl-3-methyl-4-propionylpyrazol-5-ones (HPMPRP) ……… 36

3.34 Synthesis of 1-phenyl-3-methyl-4-butyrylpyrazol-5-ones (HPMBUP) ………… 36

3.35 Synthesis of 1-phenyl-3-methyl-4-hexanoylpyrazol-5-ones (HPMCP) …………. 36

3.36 Synthesis of 1-phenyl-3-methyl-4-palmitoylpyrazol-5-ones (HPMPP) ………… 36

3.40 Synthesis of 1-phenyl-3-methyl-4-acyllpyrazolonates …………………… 36

3.41 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato magnesium II complex 36

3.42 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato copper II complex ……37

3.43 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato cobalt II complex …… 38

3.44 Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato zinc II complex …… 39

11

3.45 Preparation of 3M hydrochloric acid solution ……………………………………39

3.50 Physical and spectroscopic analysis …………………………………………… 42

3.51 Melting point determination …………………………………………….. 42

3.52 Conductivity measurement ………………………………………....... 42

3.53 Electronic spectra measurement ……………………………………………... 42

3.54 Infrared spectra measurement …………………………………………… 42

CHAPTER FOUR

4.0 Results and Discussion …………………………………………………. 43

4.10 Structure of ligands and complexes ……………………………………… 43

4.20 Physical data ………………………………………………………………….. 45

4.30 Conductivity Measurement ………………………………………………… 48

4.40 Solubility survey of ligands and complexes ………………………………… 49

4.50 Electronic spectra of ligands and complexes ………………………………….. 51

4.60 Infrared spectra of ligands and complexes …………………………………… 53

4.70 The effect of 4-acyl substituents on the infrared carbonyl stretching frequency of

metal(II) chelates of some 1-phenyl-3-methyl 4-acylpyrazolone ……………………...64

4.80 Conclusion ……………………………………………………………… 69

References ……………………………………………………………….. 71

Appendices .......................................................................................... 86

12

LIST OF FIGURES

Figure 1: Tautomeric forms of a typical β-diketone…………………………………… 6

Figure 2: Zinc (II) acetylacetonate ……………………………………………………. 7

Figure 3: Copper (II)ethylenediammine ……………………………………………… 7

Figure 4: 1-phenyl-3-methyl-4-acylpyrazolone ………………………………………. 8

Figure 5: Tautomeric forms of the 4-acylpyrazolone ……………………………………9

Figure 6: Intramolecular hydrogen bonding in the forms of the ligand ………………….9

Figure 7: Copper (II) chelate of 4-trifloroacetyl pyrazolone ……………………… 10

Figure 8: Tautomeric forms trifloroacetyl pyrazol-5-one ………………………… . 14

Figure 9: Reaction scheme for the synthesis of 1-phenyl-3-methyl-4-acylpyrazolones and

their metal complex. …………………………………………………………… 41

Figure 10: Tautomeric forms of the ligand ………………………………………….. 43

Figure 11: Structure of the metal complex ………………………………………….. 44

Figure 12: Plot of infrared carbonyl stretching frequency against molecular weight of

ligands ………………………………………………………………………………… 65

Figure 13: Plot of infrared carbonyl stretching frequency against molecular weight for Mg

(II) chelates …………………………………………………………………………….. 66

Figure 14: Plot of infrared carbonyl stretching frequency against molecular weight for Co

(II) chelates ………………………………………………………………………….... 66

Figure 15: Plot of infrared carbonyl stretching frequency against molecular weight for Cu

(II) chelates …………………………………………………………………………… 66

13

Figure 16: Plot of infrared carbonyl stretching frequency against molecular weight for Zn

(II) chelates ……………………………………………………………………………. 67

Figure 17: Plot of infrared metal-oxygen stretching frequency against molecular weight

for Mg (II) chelates ………………………………………………………………… 67

Figure 18: Plot of infrared metal-oxygen stretching frequency against molecular weight

for Co (II) chelates ……………………………………………………………………..68

Figure 19: Plot of infrared metal-oxygen stretching frequency against molecular weight

for Cu (II) chelates ……………………………………………………………………. 68

Figure 20: Plot of infrared metal-oxygen stretching frequency against molecular weight

for Zn (II) chelates …………………………………………………………………… 69

14

LIST OF TABLES

Table 1: Physical data for some 4-acylpyrazolones ……………………………………45

Table 2: Some physical data for Mg (II), Co (II),Cu (II) and Zn (II) complexes of some 1-

phenyl -3-methyl-4-acylpyrazolon-5 ………………………………………………….46

Table 3: Conductivity data. …………………………………………………………… 48

Table 4: Solubility data for the ligands and metal complexes. ……………………… 49

Table 5: Electronic spectral data for the ligands and their metal complexes ………… 52

Table 6: Infrared spectral data for the ligands and their metal complexes …………….. 53

Table 7: Infrared carbonyl and metal-oxygen stretching frequencies of the ligands and

their metal complexes …………………………………………………………………. 63

15

ABBREVIATIONS

HPMP: 1-Phenyl -3-methyl -4-acyl pyrazol-5-one

HPMAP: 1-Phenyl-3-methyl-4-acetyl pyrazol-5-one

HPMBP: 1-Phenyl-3-methyl-4-benzoyl pyrazol-5-one

HPMBUP: 1-Phenyl-3-methyl-4-butyryl pyrazol-5-one

HPMCP: 1-Phenyl-3-methyl-4-capyroyl pyrazol-5-one

HPMPRP: 1-Phenyl-3-methyl-4-propionyl pyrazol-5-one

HPMPP: 1-Phenyl-3-methyl-4-palmitoyl pyrazol-5-one

HTTA: Thenoyltrifluoroacetylacetone

DMSO: Dimethylsulphoxide

DMF: Dimethylformamide

TBP: Tris-n-butylphosphate

TOPO: Triocitylphosphineoxide

MIBK: Methylisobutylketone

EDTA: Ethylenediamminetetraacetate

THF: Tetrahydrofuran

16

CHAPTER ONE

1.0 INTRODUCTION

There has been a lot of interest in the chemistry and stereochemistry of metal

complexes in recent years because of its growing applications in both biological and chemical

processes. The chemistry of these groups of compounds was first proposed in 18931

by a

Swiss chemist, Alfred Werner who used his coordination theory of primary and secondary

valences to account for the phenomenon by which apparently all stable saturated molecules

combine to form molecular complexes.2,3

Werner showed that the properties of many

complexes formed by various transition metals could be explained by the postulate that the

metal atoms have a ligancy of six or four, with the attached groups arranged about the central

atom at the corners of a circumscribed regular octahedron or tetrahedron.4 Almost every

kind of metal atom can serve as a central atom in a complex , although some metals like the

transition metals do so more readily than others.5 When a metal atom coordinates with two or

more donor groups of a single ligand called the chelating agent , a chelate is formed. One of

the significant features of these chelating agents is that whereas complex formation may

involve more than one intermediate step, Chelation is a one step process. 6,7

Since Urbain,s work on the structure and reactivity of β-diketones in 1896,

8 these

groups of chelating agents have been of utmost importance to chemist and research workers

alike. These β-diketones are ligands bearing two carbonyl groups separated by a methylene

group. The intervening methylene group bears an active hydrogen atom.9.

The acidity of the

hydrogen atom is caused by the electron withdrawing powers of the two carbonyl groups that

flank them. Owning to electronic and field effects , the hydrogen atoms are capable of

migrating to any of the carbonyl groups giving rise to tautomers.10

1-phenyl -3-methyl -4-acyl pyrazolone , a typical β-diketone whose synthesis was first

described by Jensen, 11,12

has gained considerable popularity in recent years.13-15

The

17

structural features of these keto-enol tautomerides attracted the attention of research workers

like Okafor 16-19

and Uzokwu 20-22

who synthesized and characterized a good number of their

metal Chelates. Research into these group of β-diketones has been stimulated by their

potential application in the extraction of metal ions from acid solutions. 23-24

Some other

workers have used the 4-chloroacetyl and 4-triflouroacetyl derivatives of this ligand for the

spectrophotometric determination and extraction of trace elements from aqueous solution.

Mirza and others synthesized the benzoyl derivative of 1-phenyl-3-methyl-4-acyl- Pyrazolone

and used it in the extraction and separation of thorium from titanium, uranium and the rare

earths,27

while Hassany and Quereshi reported the extraction of group IB, IIB and III- IVA

elements using the 4-trichloroacetyl derivative of the pyrazolone moeity. Okafor 16,19,28

has

equally used the triflouro derivative in the isolation of a good number of metal chelates.

Apart from the application of these groups of compounds in qualitative and

quantitative analysis , 4-acyl pyrazolones have found application in medicine, as strong active

ingredients in analgesic 29-30

and in chromatography for the construction of mixed ligand

resins for trapping toxic metals.30

The antipyrene and some other derivatives have been found

to exhibit some biological and pharmacological properties.25,29,31

They have equally found

use in antihistamines, antipyretines, antirhematics and antiinflamatory drugs.32-33

Some

derivatives of this compound containing azo groups have also been used as antifungal and

antiparasitic agents. Recently, several pyridoxine and pyrollo- pyrazole derivatives of the

pyrazole moiety have been synthesized and reported to be useful as inhibitors of

phosphodiestrate(iv) and tumour narcosis factor.35-38

They have also been applied in the

treatment of asthma, arthritis and septic shock.35

The acyl hydrazine compounds of

pyrazolone have been found to serve as inhibitors for many enzymes and an excellent

component of many chemotherapeutic drugs for the treatment of cancer.39

Some other

derivatives have been used as corrosion inhibitors for steel in hydrochloric acid solution.40

To date, a lot of research work has appeared in literature on the structure, reactivity and

18

spectral properties of 4-acyl pyrazolones and their derivatives11-40

. This project investigates

the effect of the 4-acyl substituents on the carbonyl and metal-oxygen stretching frequencies

of some 4-acyl pyrazolones and their Mg(II) ,Co(II), Cu(II) and Zn(II) chelates.

19

CHAPTER TWO

2.0: LITERATURE REVIEW

2.10 Concept of Chelation

Chelate complexes of many metal atoms are known 41-43

and with a given chelating agent, the

properties of the complexes change from one metal atom to another. There is a great

uncertainty, that a chelating agent will react with or extract a particular metal specifically in

the presence of other metals, although chelating agents exhibit varying level of selectivity,

depending on the reacting conditions. Chelation is the formation of a ring containing a metal

atom by a multidentate ligand.44

This is said to occur when a ligand with more than one pair

of unshared electrons per molecule donates them to a metal atom,45,46

and the metal to which

electrons are donated must have available orbitals for bond formation with the chelating

agents. These unpaired electrons may be donated by coordinating groups,47,48

Like OR, OH, -

NH2, =N, or SH of the multidentate ligand. These functional groups must be well positioned

in the molecule, so as to allow a favorable chelate ring formation with the central metal atom.

Chelation is always influenced by stearic factors .49-50

Irving and Co-workers have shown

that substitution of a methyl group in the 2-position of 8-hydroxy quinoline prevented the

formation of a tris complex will Al(III), though complexes were formed with larger ions such

as Cr(II) and Fe(III).

During the formation of metal chelates, three classes of metal complexes species are

possible. They are metal chelate complexes, Ion pair complexes and additive complexes. All

these complexes are neutral compounds and there is a possibility of having two of these

complexes in solution at the same time. The formation of these complexes is governed by

certain ionic forces which are related to both the charge, the radius of the metal ion and the

relative tendencies of various metals to form bonds with electron donors. 51-52

20

2.11 Metal Chelate Complexes

These are chelates synthesized by the treatment of a cationic aquometal complex with

a chelating agent which is normally a weak acid. The reaction scheme involves the transfer of

the chelating agent from the organic phase to the aqueous phase and the subsequent

dissociation into proton and a conjugate base of the weak acid. The next step is the

displacement of the water molecule attached to the metal ion by anionic conjugate base group

in a ratio that gives a neutral metal chelate complex. The overall reaction involves bond

breakage and formation of new metal-ligand bonds. These chelates are hydrophobic and

dissolve preferentially in the organic phase53

. The interaction in this kind of complex was

described as short range, since the ions are adjacent to one another and the solvent shell of

each dissociated ion is broken.54

2.12 Ion-Pair metal complexes

Ion-pair complexes are formed as a result of long range electrostatic force of

attraction, thus it is not always necessary that the two interacting ions are close to each other.

These ion-pair complexes are not chelates. The formation of ion-pair metal complexes are in

two stages, the first stage involves the formation of the cation-metal complex in which the

aquo-ligands are substituted by anions in solution. The second stage is the attraction of this

cationic metal complex by an anionic group such that their charges are neutralized. No

covalent bond is formed between the two oppositely charged species because they are held

together by a strong electrostatic force of attraction.

2.13 Additive Complexes

These are metal chelates or ion-pair complexes with additional organic reagents, with

a lone pair of electrons at least, coordinated to the metal as a ligand solvents like TBP,

MIBK, TOPO,57,58

ethanol, DMSO can form additives complexes. Here the organic solvent is

21

acting as a reagent to displace water molecules attached to the metal complexes to from a

hydrophobic additive complexes. An additive complex involving the chelating agent can also

take place when the metals coordination number and geometry of the ligand is favorable and

the concentration of the reagent is high. 59

Another class of additive complexes are formed

when the pH of the solution is high and the metal undergoes hydrolysis. 60-61

They have a

molecular formular of MLn(OH)x where M= metal, L=anion of the ligand.

2.2 Chelation with β-Diketones

1,3 -diketones are bidentate ligands coordinating through oxygen atoms. They are weak acids

with characteristic keto-enol equilibra as show in (fig 1) below.

R

R C

O

C H R C H R 1C

O

R C

O

C

O

R 11

K eto form

R C C

O

R

O

R 11C

R C

O H

C R C

R C C R 1 C

O

R 11 R C

O

C R 1 C R 11

O H

O H

Enol Form s

O H

Fig:1 Tautomeric forms of a typical β-diketone

The presence of at least one proton on the methylene carbon atom results in keto-enol

tautomerism in these 1.3 diketones. These chelating agents can form a six membered chelate

22

ring with a large number of metals by losing one proton, for example acetyl acetone forms a

six membered chelate ring with zinc atom as shown below.

H3C

HC

H3C

C O

OC CO

O C

Zn

CH3

CH3

CH

Fig 2: Zinc (II) acetylacetonate

Ethylene diammine also complexes with copper (II) ion through the unshared pair of

electrons possessed by the nitrogen atoms in the ligand.

H2C

H2N

NH2

CH2

Cu

H2C

H2N

Cu

CH2

NH2

2+

Fig 3: Copper (II) ethylenediamine

Also included in these important class of chelating agents are HTTA, dibenzoyl methane and

the derivatives of the 4-acyl pyrazol- 5-ones. Some research workers like Lempick, and

Samuelson62

investigated the tetrakis rare earth chelates of the benzoyl trifluroacetone and

showed the possibility of laser activity in the compounds. Hinckley63

on the other hand

demonstrated the possibility of having larger isotopic shifts in solutions containing some

rare earth -diketonates, while Uzoukwu and others elucidated the chemistry and structure

of Uranium (vi) and Fe (iii) chelates of 2-thenoyl triflouroaccetone (HTTA) and concluded

they formed neutral complexes in both aqeous and acidic solutions.64

However most of the

work reported in literature on the β-diketones has been on the extraction and concentration of

metal ions 65-67

.

23

2.3 Chelation with 4-acylpyrazolones

The 4-acyl pyrazolones are members of the 1,3-diketone family. They contain both

Nitrogen and Oxygen atoms and form coordination complexes of the Six membered chelate

ring with metal ions through the oxygen atoms in them. Their chemical properties are

determined by the presence of hydrogen on the methylene carbon atom sandwiched between

the two carbonyl groups of the 1,3-diketone as shown in figure 4 below.

CH3 C O

R

O

N

C6H

5

H

N

Where R= Acetyl, benzoyl ,butyryl, Hexanoyl, palmitoyl etc

Fig 4: 1- phenyl -3-methyl -4-acyl pyrazol-5-one.

The two carbonyl groups are not isolated from one another. Due to the migration of the

methylene proton ,four structural isomers are possible as shown in the figure 5a-d.

24

C H3 C O

R

O

N

C6H

5

N

C H3 C O

R

O

N

C6H

5

N

O

C

RH

N

C6H

5

H

C H3

O

C

R

N

C6H

5

C H3

NH

O H

O

N

(a) (b)

(c)(d)

Keto form s

Enol form s

Fig 5: Tautomeric forms of the 4-acyl pyrazolone ligand.

The Enol form, Fig 5 (c) is more favourable in non-polar solvents than the keto form. Due to

conjugation and intramolcular hydrogen bonding, the enol form is stabilized relative to the

keto form. 18,68,

O

C

R

N

C6H

5

CH3

O

N

H

Fig 6 Intram olecular hydrogen bonding in the enol form s of the ligand

25

On Investigating the 4-triflouroacetyl derivative of this ligand Okafor 19

revealed that the

enolic form was more stable than the keto form and obtained experimental evidence that the

stability of the enol forms of the 4-acylpyrazolones was as a result of electronic and stearic

factors. Thus under appropriate experimental conditions the labile enolic proton of the 4-acyl

pyrazolones can be replaced by a metal ion giving a six membered chelate ring with the metal

atom at the centre, bound to an oxygen atom of the chelating agent and accepts a lone-pair of

electron donated by the oxygen of the other carbonyl group. An example is the copper (II)

complex of 4-triflouroacetyl pyrazolone shown in the figure 7.

O

ON

C6H

5

C

C

N

N

CO

O

Cu

CH3

F3

CCH

3

C6H

5

F3

Fig 7: Copper (II) chelate of 4-trifloroacetyl pyrazolone-5-one

Due to Chelation, the electron system of the 1,3-dicarbonyl group bonded to the metal is

delocalized 69,70

.

2.4 Stability of Metal Chelates

The stability of metal chelates is determined by certain factors which include, the nature

of the chelating agent, the size of the chelate ring, the nature of the central metal and the

nature of the metal ligand bond 71,72

.

2.41 Nature of the Chelating Agent

Calvin and Merit, 73,74,75

Confirmed the influential nature of the chelating agent when

they carried out studies on a series of –diketones. Acetylacetone with the pKa of 9.7 forms

more stable complexes than thenoyltriflouoroacetylacetone with pKa of 6.2. This is because

26

of the more basic nature of acetylacetone. On the other hand ,Sidgwick 76

, in 1941 pointed out

that the affinity of a ligand towards a metal atom depends on the donor atom of the ligand.

Most often, these are oxygen, nitrogen or sulphur. Oxygen and nitrogen are known to have

similar affinities for metallic ions and form stable chelates.

2.42 The Size of the Chelate Ring

Investigations have shown that for a chelate ring with minimum strain to be formed,

the bond angles of the participating atoms should be as close as possible to the normal

covalent bond angles. Application of the Baeyer strain theory shows that the five and six

membered ring compounds will be more favored among chelate compounds. But all other

factors being equal, a five-membered chelate ring will be somewhat more stable than its six

membered chelate ring analog. In general, the stability of metal chelates has been said to

increase in the order of four membered < six member ≤ five membered and chelates having

more than six members are not stable except those metal ions that tend to form linear

complexes such as Silver (I) and Mercury (II)77,78

.

2.43 The Nature of the Central Metal

There is reasonable evidence that with the transition metals, there is a gradual change

in the nature of the chelate bond, from essential ionic to covalent as the atomic mass of the

transition metal increases.79

Also the tendency towards covalent character increases with

increase in oxidation state of a transition metal. When there are two or more transition metals

having the same oxidation state, covalency increases with increase in the number of d

electrons.

2.44 The Nature of the Metal-ligand bond

There has been an attempt to classify metals based on their affinity for oxygen,

nitrogen, sulphur or a combination of these atoms.79

In the metal ligand bond, both electrons

27

utilized in the bonding are donated by an atom of the ligand. The stereochemistry and

coordination number of a metal chelate is closely related to the nature of the metal to ligand

bond. 80, 81

Most chelates with metal ligand bonds known to be covalent are observed to be

quite stable, though stereochemical factors relative to the metal to chelate itself do have

influence on the chelate stability. Substitution in the sensitive position of the chelating agent

gives a different effect. The derivatives of 8-quinolinol substituted in the second position for

example, gives less stable complexes than does 8-quinolinol itself. This has been attributed to

stearic hindrance to chelate formation caused by the substituent group.82, 83

2.5 Previous Work Done with β- Diketones

Before Jensen’s work on the 4-acylpyrazolones, 11,12

-diketones such as Acetyl

acetone and their derivatives have been used as analytical reagents for radiochemical work.

85 Recently Uzoukwu and co-workers used derivatives of ethylenediammine and 2-

thenolytriflouroacetone 64

in the extraction and concentration of different metal ions in

solution. Various studies have indicated 1-phenyl-3-methyl-4-acyl pyrazolones as powerful

analytical reagents 11-16

for a variety of metal ions. In comparism to other types of –

diketones, 4-acylpyrazolones have some advantages such as strong acidity, high chemical

stability, hydrophobicity of their chelates, 88

ability to form chelates with high distribution

ratio even in strong acid solutions, relatively low cost of synthesis and their ability to last for

a very long time. In view of this, a good number of publications11-18

describing various 4-

acyl-pyrazalones have appeared in literature and the properties of these compounds and their

chelates have been extensively studied 13,14,23,28,64,65,82

. A good number of the derivatives of

the 4-acyl-pyrazolones have been synthesized.

28

2.51 Physical Properties and Structure Elucidation

The structure elucidation of 4-acylpyrazol-5-ones presents some difficulty due to the

fact that they are potentially tautomeric heterocycles17

. Four tautomeric forms have been

found to be possible. (Fig 5) However it has been reported that the enol tautomer is more

stable than the keto tautomer in non polar solvents. Okafor 17-19

In 1980 and 1981 reported

that the 4-acylpyrazol-5-ones are practically insoluble in water but exhibit high solubility in

most organic solvents. Akama and others 89-91

in their systematic study of alkyl substituted 4-

acyl derivatives of 3-methyl -1-phenyl-pyrazol-5-ones reported that due to its slightly lower

pKa value (lower than 4.0) the 4-benzoyl derivative proved to be more efficient in the

extraction of metal ions than the 4-propionyl and 4-lauroyl derivatives which had pKa values

of about 4.2. These showed that the acid dissociation constant was insensitive to the nature of

the carbonyl group79

. Uzokwu92

equally reported that the pKa value of the corresponding 4-

triflouroacetyl and 4-trichloroacetyl derivatives are lower than the other derivatives and has

been proved to be even more efficient analytical reagents for the determination of metal ions.

Okafor in 1982 19

investigated and reviewed the triflouroacetyl derivative of the 1-phenyl-

3-methyl-4-acyl pyrazol-5-ones and observed that only the enol form of the ligand was

capable of existing in stable form.

29

N

N

C

O

CH3

Cf3

C6H

5

C O

C N

N

C

O

CH3

Cf3

C6H

5

C

C

C

H

O

(I) (II)

N

N

C

O

CH3

Cf3

C6H

5

C

C N

N

C

CH3

Cf3

C6H

5

C

C

C

H

(III)

O H

O

O H

(IV )

H

Fig 8 :Tautomeric forms of 4-triflouroacetyl pyrazol-5-one

The results of his investigation revealed that only one form of the triflouro acetyl derivative

of the 4-acyl pyrazolone existed even when recrystalized from different solvents. He

concluded that the forms obtained from recrystallization from ethanol and water were the

same as revealed by detailed infrared and proton Nmr studies, only that the former contained

one molecule of water of crystallization. This observation refuted the claims of Hasany and

Quereshi 24

who reported that by Jensen’s method, 12

they obtained two forms of the 4-

triflouro-1 phenyl-3-methylpyrazo-5-one when recrystalized from different solvents, (ethanol

and benzene). The enol form being yellowish and the keto form colorless. He went further to

explain that the probability of the form (I) existing is very slim due to the presence of

electron withdrawing groups (C=O, C-N and CF3 which are withdrawing negative charge

from the carbon atom carrying the negative charge. Finally he suggested the possibility of

(II), (III) and (IV) existing and isolable with structure (IV) most likely to be isolated in stable

30

form, this he attributed to the electron releasing nature of C6H5 which counter balances the

electron withdrawing properties of –CF3 group, thus the hydroxyl proton in the structure (IV)

will be more labile than the hydroxyl proton in the structure (III).

2.52 Isolation and Spectroscopic Studies

Uzoukwu and Duddeck 86

in 1998 studied the spectroscopic properties of the metal

complexes of the 4-adipoyl and 4-sebacoyl bis 1-phenyl-3-methyl pyrazolones and using the

analytical and UV spectral data showed that some of the metals formed hydrated complexes

with the chelating agents. They represented these complexes with the general formular

ML.XH20 where M=metal ion, L is 4-acyl bis (1-phenyl methyl pyrazolones) dianion and

x=0,1,11/2

or 2. Molar conductivity measurements of 104M solutions of the complexes, in

DMF recorded values in the 2-5 Ω1cm

2 mol

1 range indicating that all the complexes are

neutral. The infrared spectral data of the metal complexes showed some broad bands at 3150-

3410 cm-1

, indicative of water molecules of the hydrated complexes 87

. The carbonyl

vibrational frequencies which occurred at 1626cm-1

(H2SP) and 1632cm-1

(H2Adp) shifted to

the lower region in the IR spectra of the metal complexes indicating the involvement of C-O

bond in chelation with the metal ion. They assigned the Unique absorption frequencies

appearing below 500cm-1

in the IR spectrum of the metal (II) chelates to asymmetric

stretching frequency vibration of the metal oxygen bonds 88

.

Apart from the works of Uzokwu and Duddeck 86-88

Okafor93

synthesized the rare

earth chelates of 1-phenyl-3-metltyl 4-Benzoyl pyrazol-5-one and studied their spectral

properties. He observed from the electronic spectra, that contrary to general rule, that there

was no bathochromic shift on chelation to a metal as obeyed by other diketonates. The

ligands and complexes had virtually identical absorption maxima, indicating that the π -

bonding system in each ligand anion was almost intact, only the s-orbital of the oxygen atoms

(one orbital being non-bonding and the other having lost a proton) are substantially involved

31

in bonding with the metal ions. Thus there was little or negligible π -electron interaction

amongst the three chelate rings. He also observed from the IR spectral data of both the

complexes and the ligands that there were similarities and a few marked changes in

absorption bands. The main changes observed in the spectra of the ligands when complexed

included the disappearance of the OH-O absorption band centered at 2600cm-1

and the shift

of the C=O stretching frequency from 1640cm-1

in the ligand to 1608cm-1

(vas C=O). The

absence of absorption peaks between 1800cm-1

and 1608cm-1

in all the trischelates was taken

as an evidence of six oxygen atoms of the -diketonate being bonded directly to the rare

earth ion.The manganese (II) and Zinc (II) Complexes of some 1-phenyl-3-meltyl-4-acyl

pyrazolones have been studied and the UV spectral data of both the Mn(ii) and Zn(II)

complexes in chloroform showed absorption bands near 252nm and 286nm, ascribed to π- π*

Intra ligand transition. The IR spectral properties were also studied and it was stated that the

bathochromic shifts in the vas C=O of the metal complexes which occurred at 10-20Cm-1

from the ligand was an evidence that the C=O group of the free ligand was involved in the

Chelation process. It was also observed that the stability of both the CO-M and C=O bonding

systems did not follow any particular trend with respect to the nature of the 4-acyl

substituent. However the absorption bands observed for the 4-trichloroacetyl pyrazolone

complexes of both metals were relatively higher, vas C-O (Mn 1620cm-1

, Zn 618cm-1

) and

vas C O-M (Mn 470cm-1

, and Zn 488cm-1

) than those for the alkyl substituted 4-acyl

derivatives and this was attributed to differences in the nature of the electronic and stearic

interactions between these different groups [94]

.

The complexes of the acetyl, propionyl Butyryl triflouroacetyl and capyroyl with

lanthanides,uranyl, monovalent and divalent metals have been synthesized by Okafor and

others 16,18,19,25,41

and spectroscopic studies carried out on them. They reported a general

formula LaA3 XH2O.YC2H5OH for lanthanide chelates of the 4-acylpyrazolones , where La

is the lanthanide, A is the 4-acyl-pyrazolone anion, X=2 and Y=0 or ½ ,while the other group

32

of metals gave complexes of composition MAn. XH2O where n is charge of the metal M and

X=O, 1, or 2. The results of their investigation also showed that the magnitude of the M-O

stretching frequencies for the transition metals followed very closely the Irving-Williams

stability order 18,79,96

Cu>Ni>Zn>Co>Mn. Some other workers, 23, 24,25

have synthesized other

derivatives of the pyrazole moiety and confirmed that their formula corresponds to the one

reported by Okafor above.

2.60 Previous Works Done on Metal Chelates of β-diketones

2.61 The Chemistry of Magnesium

Compounds of magnesium have been known from ancient times, though nothing was known

of their chemical nature until the seventeenth century 97

. Magnesium like its heavier

congeners Ca, Sr and Ba, occurs in crystal rocks mainly as the insoluble carbonates, sulphates

and silicates. Estimates of its total abundance depend sensitively on the geochemical model

used. Large land masses such as Dolomites in Italy consist predominantly of the magnesium

limestone mineral dolomite [MgCa(CO3)2] and there are substantial deposits of magnesite

(MgCO3) epsomite (MgSO4.7H2O) and other evaporites such as carnalite (K2MgCl4.6H2O)

and langbeinite [(K2Mg2(SO4)3].98

Silicates are represented by the common basaltic mineral

olivine [(Mg,Fe)2SiO4] and by soapstone (talc) Mg3Si4O10(OH)2] and Micas. Magnesium is

produced on a large scale either by electrolysis or by silicothermal reduction. The

electrolytic process uses ester fused anhydrous MgCl2 at 7500C or partly hydrated MgCl2

from sea water at a slightly lower temperature. The silicothermal process uses calcined

dolomite and ferrosilicon alloy under reduced pressure at 11500C.

2(MgO.CaO) + FeSi 2Mg + Ca2SiO4 + Fe

Magnesium like other group 2 metals are not noted for their ability to form complexes. The

factors favoring complex formation are small highly charged ions with suitable empty

33

orbitals of low energy which can be used for bonding.2 Mg usually forms complexes in

solution with oxygen-donor ligands ,(EDTA). It also forms a few halide complexes such as

[Net4]2 [MgCl4] and a very important complex called chlorophyll where magnesium is at the

centre of a flat heterocyclic organic porphyrin ring system , in which four nitrogen atoms are

bonded to the magnesium .(99)

Chlorophyll is the green pigment in plant which is responsible

for photosynthesis. Organometallic compounds of magnesium have also been isolated, the

grignard reagents are the most important organometallic compounds of Mg and are probably

the most extensively used of all organometallic reagents. Grignard reagents contain a variety

of chemical species inter linked by mobile equilibrium whose position depends critically on

at least five factors: 100

(i) the stearic and electronic nature of the alkyl (aryl) group R (ii) the

nature of the halogen X (size, electron-donor power etc) (iii) the nature of the solvent (Et2O,

THF, benzene etc) (iv) The concentration and (v) the temperature of the species present. It

may also depend on the presence of trace impurities such as H2O or O2.101

Grignard reagents

are normally prepared by the slow addition of the organic halide to a stirred suspension of

magnesium turnings in the appropriate solvent and with rigorous exclusion of air and

moisture. The reaction which usually begins slowly after an induction period can be initiated

by addition of a small crystal of iodine and this penetrates the protective layer of oxide

(hydroxide) on the surface of the metal. The order of reactivity of RX is I>Br >Cl and alkyl

>aryl.102

. They have been applied in the synthesis of alcohols, aldehydes, ketones ,carboxylic

acids, esters and amides and are probably the most versatile reagents for constructing C-C

bonds by carbonion (free-radical) mechanism103

A related class of compounds, the alky-

magnesium alkoxides can also be formed by the reaction of MgR2 with an alcohol or ketone

or by reaction of Mg metal with the appropriate alcohol and alkyl chlorides in

methylcyclohexane solvent104-105

.

34

4M gEt2 + 4ButO H (E tM gDBut)4 +4C

2H

6

2M gM e2 + 2ph

2CO

Et2O

(M e M gO CM ph2

.E t2O )

2

2.62 Review of Previous Works Done on Magnesium Chelates of β-diketones.

Majority of the works reported on the Mg(II) complexes of 1,3-diketones are based on

the concentration and extraction of metals using 4-acylpyrazolone ligands 106-107

. Bukowky

and others reported the extraction of Mg(II) Ion from neutral solution by an 1so-arylalcohol

solution of HPMBP 106

. The extraction was quantitative when oxygen containing solvents

were used and the medium weakly alkaline.68

Mirza 107

in 1970, reported the preparation of 28

Mg in a nuclear reactor and stated a procedure for extraction of micro amounts of 28

Mg from

a mixture of radioactive materials. There are also reports on the structure and IR spectral

studies of magnesium complexes of 4-acyl pyrazolones in literature. Okafor26

has reported

the synthesis and infrared spectral studies of the magnesium chelate of 1-phenyl-3-methyl-4-

trifluoroacetyl pyrazolones. He observed from analytical results that the complex has the

molecular formula M(PMTFP)2. 2H2O( where M=Magnesium and PMTFP is the ligand

anion) with negligible molar conductance values in DMF solution showing that the complex

was neutral. He also reported that the Benzoyl derivative of the 4-acylpyrazolone gave a

white colored complex with magnesium (96)

and used proton NMR spectral studies to deduce

the number of associated water. The infrared spectral data showed a shift in the carbonyl

stretching frequency from 1640cm-1

in the ligand to 1635cm-1

in the metal complex showing

that there was complexation through the C=O of the chelate ring.

2.70 Chemistry of Cobalt

Cobalt is a very tough metal with high tensile strength. it is relatively unreactive in

H2O, H2 or N2, though it reacts with steam forming CoO. It is oxidized when heated in air and

burns at white heat to CO3O4. Co dissolves slowly in dilute acid but rendered passive by

35

concentrated HNO3. It combines readily with halogens and at elevated temperature with S, C,

P, As and Sn.2 The most common oxidation states of cobalt are the +II and+ III, [Co(H2O)6]

2+

and Co(H2O)6]3+

are both known but the later is a strong oxidizing agent and in aqueous

solution, it is acidic. The +Ill oxidation state is the most prolific oxidation state of cobalt,

providing a variety of kinetically inert complexes. These complexes are virtually low spin

octahedral complexes. A major stabilizing influence being the high CFSE associated with the

t2g6

configuration, the maximum possible for any dx configuration. Even [Co(H2O)6]

3+ is a

low spin complex, but it is such a strong oxidizing agent that it is unstable in aqueous

solution as mentioned earlier. Only a few simple salt hydrates such as the blue Co2(SO4)3

.18H2O and MCo(SO4)2 .12H2O (M=K, Rb, Cs, NH4) which contain the hexa aquo ion and

CoF3. 3½H2O can be isolated.109

As a result of the kinetically inert nature of cobalt (III)

complexes, they are prepared by addition of the ligands to an aqueous solution of cobalt (II)

salt and the cobalt (II) complex formed is oxidized by some convenient oxidant in the

presence of a catalyst such as active charcoal 110

. Compounds of cobalt (III) formed with N-

donor ligand like the NO2 ion are (Na3[Co(NO2)6]), orange sodium cobaltinitrite which is

used in aqueous solution for the quantitative precipitation of K+ as K3(Co(NO2)6] in classical

analysis. Treatment of this compound with flourine yields K3(CoF6) whose anion is notable

not only as the only hexa halogeno complex of cobalt(III) but also for being high spin and

hence paramagnetic, with a magnetic moment at room temperature of nearly 5.8BM. The

complexes of cobalt (III) with O-donor ligands are generally less stable than those of with N-

donors, although the dark green Co(acac)2 and M3[Co(C2O4)3 and M3[Co(C2O4)3] complexes

formed from the chelating ligands acetylacetonate and oxalate are stable. Other caboxylate

complexes such as those of acetate are however less stable but are involved in the catalysis of

a number of oxidation reactions by Co11

carboxylates.112

The chemistry of cobalt(III)

complexes is similar to those of chromium(III) but a noticeable difference between the two is

the smaller susceptibility of the former to hydrolysis, though limited hydrolysis leading to

36

polynuclear cobaltammines with bridging OH-groups. Other common bridging groups are

NH2-, NH3

2- and NO2

- and singly, doubly and triply bridged species are known such as

the bright b lue [(NH3)

5 Co-NH

2-Co(NH

3)

5]5+

garnet red- [NH3)

4Co

O H

O HCo (NH

3)

4]4+ and red [(NH

3)

3O H

O H

Co Co

NH2

(NH3)

3]3+

But the most interesting of the poly nuclear complexes are those containing O-O bridges,113

for example, the brown [NH35 Co-O2-Co(NH3)5]4+

green paramagnetic [(NH3)5 Co-O2-Co(NH3)5]5-

, red [(NH3)4 Co(µ-NH2)-µ-O2) Co(NH3)4]4-

and

brown[(NH3)4 Co(µ-NH2)-µ-O2) Co(NH3)4]3+

The +II oxidation state of cobalt gives rise to simple salts with all the common anions and

they are readily obtained as hydrates from aqueous solutions. The cobalt (II) carboxylates

such as the red acetate, Co(O2CMe)2 .4H2O are known.They are monomeric and in some

cases the carboxylate ligands are unidentate 114

. The acetate is employed in the production of

catalyst used in certain organic oxidations and also as a drying agent in oil based paints and

varnishes115

. Many of the hydrated salts and their aqueous solutions contain the octahedral

pink [Co(H2O)6]2+

, ion and bidentate N-donor ligands such as en, bipy, phen and

octahedral cationic complexes [Co[L-L)3]3+

which are much more stable to oxidation than is

hexamine [Co(NH3)6]2+

acetyl Acetonate (Acac) yields the orange [Co(acac)2H2O)2] which

has the trans octahedral structure and can be dehydrated to Co(acac)2.This attains octahedral

coordination by forming the tetrameric species. [Co(acac)2]4]. Tetrahedral complexes are also

common being formed more readily with cobalt(II) than with the cation of any other truly

transition element (excluding ZnII). Thus in aqueous solutions containing [Co(H2O)6]

2+ and in

acetic acid the tetrahedral [Co(O2CMe)4]2-

occurs. Anionic complexes [CoX4]2-

are formed

with the unidentate ligands X=Cl, Br, I, SCN and OH and a whole series of complexes

[CoL2X2] (L=ligand with group 15 donor atom X=halide, NCS) has been prepared in which

37

both stereochemistries are found116

. The most obvious distinction between the octahedral and

tetrahedral compounds is that in general, the former are pink to violet in colour whereas the

later are blue as exemplified by the well known equilibrium.

[Co(H2O )

6]2+ + 4C l

-[CoC l

4]2 + 6H

20

-

pink blue

Square planar complexes of cobalt(II) are also well documented and including

[Co(phthalocyanine)] and [Co(CN)4]- as well as [Co(salen)] and complexes with other Schiff

bases.117

These complexes are a invariably low spin with magnetic moments at room

temperature in the range of 2.1-2.9BM. Indicating the presence of an unpaired electron. They

are primarily of interest because of their oxygen-carrying properties, The uptake of dioxygen

which bonds in the bent configuration C o O

O

is accompanied by the attachment of a

solvent molecule trans to the O2 and the retention of the single unpaired electron. There is

fairly general agreement, based on electron spin resonance evidence, that electron transfer

from metal to O2 occurs just as in the bridged complexes producing a situation close to the

extreme represented by low-spin CoIII

attached to a super oxide ion O2-. The opposite

extreme represented by CoII-O2, implies that the unpaired electron resides on the metal with

the dioxygen being rendered diamagnetic by the consequent spin pair. However, the extent of

the electron transfer is probably determined by the nature of the ligand trans to the O2118

.

The five coordinate OH compounds which have been characterized included [CoBr-

NC2H4NMe2)3]+

which is a high spin with 3 unpaired electrons and is trigonal bipyramidal

(imposed by “tripod” ligand) and [Co(CN)5]3-

which is a low spin with an unpaired electron

and is square pyramidal. The absence of a simple hexacyano complex is significant as it

seems to be generally the case that ligands such as CN- which are expected to induce spin

paring favor a coordination number 4 for CoII rather than 6; The planar [CoCdiars)2(ClO4) is

38

a further illustration of this.Presumably Jahn-Teller distortion, which is anticipated for the

low spin t2g6 and eg

1 configuration is largely responsible.

119

2.71 Previous Work Done on Cobalt with β-diketones.

Recently, Pamar and Teraiya in (2009)

120 synthesized and characterized the cobalt complexes

of some 5-pyrazolone based Schiff-base ligands and observed that the OH stretching

frequencies of the free ligands is displaced to the 3350cm-1

- 2800cm-1

region due to the

internal hydrogen bonding of the OH with N=C.They also assigned displacement of the C-O

stretch (1305-1320cm-1

) of the ligand to a higher (1310-1330cm-1

) in the complex to the

participation of the 5-OH of the pyrazolone in chelation. The far infrared spectra of the metal

chelates showed bands at 490-500cm-1

and 400-415cm-1

, indicative of the Co-N vibration of

azomethine nitrogen consistent with octahedral geometry.

The cobalt complexes of 4- adipoyl and 4-sebacoyl derivatives of bis (1-phenyl-3-methyl

pyrazolone have been characterized by Uzoukwu and others 122

and assigned electronic data

values of max =244nm for 4-adipoyl and 250nm for the 4-sebacoyl derivatives. They

ascribed the sharp infrared peaks occurring at 448cm-1

for the 4-adipoly derivative and

474cm-1

for the 4-sebacoyl derivative to the Co-O asymmetric stretching frequency. They

concluded that cobalt (II) ion formed a dimeric complex Co(SP)2 with the 4-sebacoyl

derivative and a monomeric complex with the 4-adipoyl derivative. The cobalt (II) complexes

of some other derivatives of the 4-acyl pyrazolones have been synthesized,87

and the

microanalytical data on the complexes showed that the mode of interaction between Co2+

and

the ligands is in the mole ratio of 1:2. These complexes are bischelates, associated with two

molecules of water of crystallization from the aqueous medium. Okafor has also worked on

the cobalt (II) complexes of benzoyl (96)

, and triflouro acetyl 28

derivatives of the 4-acyl

pyrazolones and characcterised them by elemental, electronic ,infrared spectral, proton and

carbon 13 NMR spectral studies. Some other workers 121,122

have equally studied the

39

synthesis and characterization of Cu (II) complexes of some other non pyrazolone based

derivative of the -diketone family.

2.80: The chemistry of copper

The name copper and the symbol Cu are derived from eascyprium (Later cuprum) since it

was from Cyprus that the Romans first obtained the copper metal. It is a very strong and

stable metal, Unreactive with hydrogen, but the reddish brown precipitate obtained when

aqueous CuSO4 is reduced by hypophosphoric acid (H3PO2) is largely CuH. They form two

oxides Cu2O (yellow or red) and CuO (black) when the metal is heated in air or O2, Cu2O

being favoured by high temperature .125

Copper is also attacked by sulphur and halogens to

form Cus, the more stable Cu2S, CuCl2 and CuBr2 etc. The reactions of copper metal are

generally assisted by the presence of air. Non-oxidizing acids have little effect but Conc

H2SO4, and Conc HNO3 can dissolve the metal 126

.

Copper exists in two common oxidation states, the +1 (cuprous) and +2 (cupric)

oxidation states. Because the oxidation potential for the Cu+/Cu

2+ half reactions is less

negative than for Cu/Cu+ half reactions, any oxidizing agent strong enough to oxidize copper

to copper atom is also able to oxidize the copper(I) to copper (II) ion.

Cu(S )

Cu+(aq)

+ e -E

o= 0.52v

Cu+ (aq) Cu2+ -E

o0.15(aq)

+ ev = 0.15v

Cu(I) forms diamagnetic compounds coordinated to polarized ligands easily in aqueous

solution. Cu(1) Ion is very unstable with respect to disproportionation.

2Cu(I) Cu(II) + Cus

Nevertheless, CuI

can be stabilized either in compound of very low solubility or by

complexing with ligands having π-acceptor character. Its solutions in MeCN are stable and

40

electrochemical oxidation of the metal in this solvent provides a convenient preparative route

127. Tetrahedral complexes such as (Cu(CN)4]

3- [Cu(py)4]

+ and [Cu(L-L)2 e.g L-L=bipy,

phenl) are known, but lower coordination numbers are possible such as in linear (CuCl2)-

formed when CuCl is dissolved in hydrochloric acid and in K[(Cu(CN)2] which solid

contains a trigonal, almost planar Cu(CN)2 units linked in polymeric chain.The + (II)

oxidation state of copper provides by far the most familiar and extensive chemistry of copper,

forming simple salts with most anions except CN and I- which instead, form covalent Cu

I

compounds which are insoluble in water. The salts are predominantly water-soluble, the blue

color of their solutions arising from the [Cu(H2O))6]2+

ions and they frequently crystallize as

hydrates 128

. The most common coordination number of copper(II) are 4,5 and 6, but regular

geometries are rare and the distinction between square-planar and tetragonally distorted

octahedral coordination is generally not easily made. The reason for this is ascribed to the

Jahn- Teller effect arising from the unequal occupation of the eg pair of orbitals (dz2 and dx

2-

y2) when a d

9 ion is subjected to an octahedral crystal field. Occasionally as in solid KAlCuF6

for instance, this results in a compression of the octahedron ie “2+4” coordination (2 short

and 4 long bonds).129

The usual result however is an elongation of the octahedron ie “4+2”

coordination. (4 short and 2 long bonds) as is expected if the metals dz2 orbital is filled and

its dx2-y

2 is half filled. In its most extreme form, it is equivalent to the complete loss of the

axial ligand leaving a square planar complex. A few 5-coordinate complexes of copper (II)

such as [Cu(bip)3]+ in its perchlorate has been described as square pyramidal or distorted

octahedral130

. The Macro cyclic N-donor, phthalocyanine forms a square-planar complex and

its substituted derivatives are used to produce a range of blue to green pigments, which are

thermally stable to over 5000C and are widely used in inks, paints and plastics. In alkaline

solutions biuret, HN(CONH2)2 reacts with copper(II) sulfate to give a characteristic violet

color due to the formation of the complexes (Cu2(µ-OH)2 (NH CoNH CoNH)4)2-

. This is the

basis for the biuret test in which an excess of NaOH solution is added to the unknown

41

material together with a little CuSO4 solution, a violet color indicates the presence of protein

or other compounds containing a peptide linkage.

Copper(II) also forms stable complexes with O-donor ligands. In addition to the hexaquo Ion,

the square planar -diketonates such as [Cu(acac)2] (which can be precipitated from

aqueous solution and recrystalized from non aqueous solvents) and tatrate complexes used in

fehling’s test are well known. 131

2.81:Previous work on the Copper Chelates of β-diketones

Most of the work done on the copper complexes of 4-acyl pyrazolones were on the extraction

and concentration of the metal from aqueous and acidic solution. 23,24,132,133,134

Zolotov others

133 extracted a number of copper chelates from aqueous solutions and deduced from micro

analytical data that the mode of interaction between Cu2+

and 4-acyl pyrazolones is in the

metal ligand mole ratio of 1:2 and reported the formation of dirty green complexes.

Hassany24

reported the extraction of copper complexes with similar metal ligand composition

and concluded that all the complexes were hydrophobic and are soluble in chloroform,

dioxane ,DMF and DMSO. Akama and others23

also extracted copper(II) ions from aqueous

solutions and reported that the formation of a stable and hydrophobic metal complex were

one of the properties responsible for the efficient extraction of Cu2+

ions from aqueous and

acidic solutions. The thermal decomposition of copper complexes of some-1-phenyl-3-

methyl-4-acyl pyrazolones in air were studied in 1995 and it was reported that the melting

point of the complexes decreases linearly in increasing molecular weight 137

In the last two decades, a lot of information have appeared in literature on the spectroscopic

properties of copper(II) complexes of 1-phenyl-3-methal-4-acyl pyrazones-5-ones and their

derivatives. The Cu(II) complexes of 4-adipoyl and 4-sebacoyl derivatives of bis (1-phenyl-3-

methyl pyrazol-5-one) have been synthesized and characterized 87

. The spectral data obtained

42

showed that the Cu(II) chelate of the 4-adipoyl derivative (H2Adp) existed as a -diketone

while the 4-sebacoyl derivative(H2SP) existed keto-enol tautomer. Though subsequently the

4-adipoyl derivative underwent rearrangement to the ketoenol tautomer.

Okafor 96

synthesized the copper(II) complex of 1-phenyl-3-methyl-4-benzoyl

pyrazolone, characterized it by infrared spectral studies and reported a 471cm-1

M-O

stretching frequency band for the complex. Uzoukwu and others138,139

in 1992 studied the

electronic and vibration properties of a series of copper complexes of some 1-phenyl -3-

methyl 4-acyl pyrazolone-5 and observed that the complexes in chloroform had two bands in

the UV region near 251nm (E2500) and 294nm (E 2000). Each of these bands suffered a

bathochromic shift by 1-5nm with respect to identical bands in the UV spectrum of the ligand

and these he ascribed to intra ligand -* transitions. They concluded that the -bonding

system of the ligand is almost intact in the ligand anion of the complex, thus making it

possible for the Cu2+

to form a bond with the ligand by the displacement of the proton of

the OH group of the ketoenol tautomer of the 4-acyl pyrazolone by the Cu2+

Ion. Some other

workers140

corroborated this assertion using infrared evidence which showed a

bathochromic shift of the asymmetric stretching frequencies of the C=O group of the ligand

on complex formation. The infrared data further suggested that the stability of the Cu-O

bond in the complexes decreases with increase in carbon chain of the 4-acyl substituent while

the reverse is the case for the Cu-O of the Cu=O-Cu bonding system. Hence a magnetic

moment of between 1.175-1:82B.M at 298K was suggested for all the complexes.

2.90: Chemistry of Zinc

Zinc occurs in nature in the form of zinc sulphide (which is known as Zinc blende and

ZnCO3 (Calamine). It is a silvery solid with blush lustre when freshly formed. Zinc tarnishes

quickly in moist air and combines with oxygen, sulphur, phosphorus and the halogen on

being heated. Zinc dissolves in non oxidizing acids to liberate hydrogen and oxidizing acids

43

to form a variety of oxides 141

. In view of the stability of the filled d shell, the Zinc element

shows a few of the characteristic properties of the transition metals despite their position in

the d block of the periodic table. Thus Zinc show similarities with the main group metal

magnesium, many of their compounds being isomorphous and displays the class-a

characteristics of complexing readily with O-donor ligands. 142

On the other hand Zinc has a

much greater tendency than magnesium to form covalent compounds, and it resembles the

transition metals in forming stable complexes not only with O-donor ligand but with N- and

S-donor ligand and with halides and CN-143

Most compounds of Zn2+

are diamagnetic and

like those of Mg11

are colorless.The almost invariable oxidation state of Zinc is + 2 and it

forms salts of different compounds in form of oxides, halides and chacogenides.144

Salts of

other anions are also known, oxo salts are often isomorphous with those of Mg11

but with

lower thermal stabilities. The carbonates, nitrates and sulphates all decompose to the oxides

on heating. Several zinc salts such as the nitrates, perchloates and sulfates are very soluble in

water and form mostly one hydrate salts. [Zn (H2O)6]2+

is probably the predominant aquo

specie in solutions of Zinc salts. Aqueous solutions are appreciably hydrolyzed to species

such as [M(OH)(H2O)x]+ and M2(OH)(H2O)x]

3+ and a basic salt such as ZnCO3.2H2O

Zn(OH)2 . 2H2O can be precipitated. Distillation of Zinc acetate under reduced pressure

yields a crystalline basic acetate [Zn4O(OCO Me)6]. The molecular structure of this

compound consist of an oxygen atom surrounded by a tetrahedron of Zn atoms bridged across

each edge by acetates. It is isomorphous with the basic acetate of beryllium but in contrast,

the Zn2+

compounds hydrolyses rapidly in water. The coordination chemistry of Zinc(II)

although less extensive than for preceding transition metals is still appreciable. It does not

form stable flouro complexes but with the other halides it forms complex anions [MX3]- and

[MX4]2-.

Tetrahedral complexes are the most common type and are formed with a variety of

O-donor ligands, more stable ones with N-donor ligands such as NH3 and amines. Some of

the apparently 3-coordinate complexes have higher coordination numbers because of the

44

aquation or association but no doubt because the ligand is bulky. 2- coordinated Zn occurs in

[ZnN.(CMe3)[SiMe3]2, the first homoleptic Zinc amide to be structurally characterized 145,146

.

Complexes of higher coordination numbers are often in equilibrium with the

tetrahedral form and may be isolated by increasing the ligand concentration or by adding

large counter ions e.g [M(NH3)6]2+

, [M(en)3]2+

or [M(bipy)3]2+

.With acetylacetone, Zinc

achieves both 5 and 6 coordination by trimerizing to [Zn(acac)2]3. Five coordination is also

found in adducts such as the distorted trigonal bipyramidal [Zn(acac)2 (H2O)] and [Zn

(glycinate)2 H2O)2] while the hydrazinium sulfate (N2H5)2 Zn(SO4)2 contains 6-coordinated

Zinc. This is isomorphous with Cr(II) compounds and in the crystalline form consists of

chains of ZnII bridged by SO4

2- Ions with each Zn

2+ additionally coordinated to two trans

N2H5+ ions. The Zinc porphyrin complex [Zn(porph) THF] (porph=Meso-tetraphenyl

tetrabenzo porphyrin) is approximately square pyramidal with THF at its apex. Being

somewhat flexible, the porphyrin is distorted into a saddle shape, and displaced above its

mean plane . 147

Compounds with coordination numbers higher than 6 are rare and in some

cases are known to involve chelating NO3- ions which not only have a small bite but may also

be coordinated asymmetrically so that the coordination number is not well defined1.

2.91:Previous Work Done on Zinc(11) Chelates of β-diketones

A good number of publications have appeared in literature on the Zn(II) chelates of

the 4-acyl pyrazolones and their derivatives18,28,87,94,96

Uzoukwu in 1992 synthesized some

derivatives of the 4-acyl pyrazolones and used them in extraction of Zn(II) ions from acid

media.94

The spectroscopic data obtained from UV, IR and HNMR analysis showed that the

stability of both CO-M and C=O bonding system did not follow any trend, with respect to

the nature of the 4-acyl substituent; unlike in similar reports14, 138

. However he observed that

the aryl substituted 4-acyl derivatives had higher νas C=O than those of the alkyl substituted

4-acyl derivatives. The Zn(II)complex of 4-benzoyl pyrazolone has also been synthesized96

45

and micro analytical data predicted a molecular formula of Zn(PMBP)2 .YC2H5 indicative of

the presence of coordinated solvent molecules . Careful interaction of the protons signals in

the proton Nmr spectra revealed one molecule of C2H5OH associated with the molecules of

the metal complex. Ozaki and other148

reported the solvent extraction of Zinc with 1-(2-

chloro phenyl) 3-methyl-4-aryl pyrazolone, while Umetani and Matsui 149,150

reported the

procedure for extracting micro amounts of Zn(II) and cadmium with 4-Benzoyl -3-methyl-1-

phenyl-5-pyrazolone and Quaternary Ammonium salts dissolved in organic solvents. They

also reported the liquid- liquid distribution of 4-acyl-3-methyl-1-phenyl 5-pyrazolon and their

Zinc complexes and stated that the extraction was quantitative when oxygen containing

solvents were used and the medium weakly alkaline.151

2.92: SPECTROSCOPIC TECHNIQUES USED IN THE STUDY OF LIGANDS AND

METAL COMPLEXES

2.93 Ultraviolet/ Electronic Spectroscopy

Electronic spectra of metal ions and complexes are observed in the visible and

Ultraviolet regions of the electromagnetic spectra.152

This type of absorption

spectroscopy shows the particular wavelengths of light absorbed, that is the particular

amount of energy required to promote an electron from one energy level to a higher

energy . The visible and ultraviolet spectra of compounds are associated with

transitions in electronic energy levels. The transitions are generally between a

bonding or lone pair orbital and an unfilled non-bonding or anti-bonding orbital. The

wave length of the absorption is the measure of the separation of the energy levels of

the orbitals concerned 153

. The highest energy separation is found when electrons in

bonds are excited, giving rise to absorption in the 120-20nm (1nm=10-

7cm=10Ǻ=1mµ) range. This range known as the vacuum Ultraviolet, (since air must

be excluded from the instrument) is both difficult to measure and relatively

46

uninformative. Above 200nm, however excitation of electrons from p, d , -orbitals

and particularly, -conjugated systems gives rise to readily measured and informative

spectra. The interpretation of the spectra provides a most useful tool for the

description and understanding of the energy levels present.

2.94: Infrared Spectroscopy

The infrared radiation refers broadly to that part of the electromagnetic spectrum

between the visible microwave regions and the far infrared regions of the electromagnetic

spectrum. Of greatest practical use to the chemist is the limited portion between 4000cm-1

at

high frequency end to 400cm-1

at the low frequency end, though there has been some

interest in the near IR (14,290-4000cm-1

) and the far IR regions (700-200cm-1

). 154

The infrared spectrophotometer consists of a source of infrared light, emitting radiation

throughout the whole frequency range of the instrument. This light is split into two beams of

equal intensity, and one beam is arranged to pass through the sample to be examined. If the

frequency of vibration of the sample molecule falls within the range of the instrument, the

molecule may absorb energy of this frequency from the light. The spectrum is therefore,

scanned by comparing the intensity of the two beams after one has passed through the sample

to be examined. The wavelength range, above which the comparism is made, is spread out in

the usual way with a prism or grating. The whole operation is done automatically in such a

way that the usual finished spectrum consists of a chart showing downward peaks,

corresponding to absorption plotted against wavelength or frequency to allow for variations

in the spectrometer. Spectras are often calibrated against accurately known band of the

spectrum of polystyrene, the peaks of one or more of these bands being superimposed on the

spectrum which is to be taken.[154]

Compounds may be examined in the vapor phase, as pure

liquids in solution and in the solid state. These molecules can absorb radiation energy from

the region stated above and convert them into molecular vibrations resulting in energy

47

vibrations patterns known as the infrared spectrum.155

Some structural groups of atoms give

rise to vibrations bands at or near the same frequency regardless of the structure of the

molecules. The theoretical number of fundamental vibrations (absorption frequencies) will

seldomly be observed because overtones (multiples of a given frequency) and combination

tones (sum of two other vibrations) increase the number of bands whereas other phenomena

reduce the number of bands156

. The following will reduce the theoretical number of bands:

a. Fundamental frequencies that fall outside of the 4000-400cm-1

region

b. Fundamental bands that are too weak to be observed

c. Fundamental vibrations that are so close that they coalesce

d. The occurrence of a degenerate bands from several absorptions of the same frequency

in higher symmetrical molecules.

e. The failure of certain fundamental vibration to appear in the IR because of the lack

of changes in molecular dipole.

Essentially, these properties help a chemist in obtaining some usefull structural

information by simple inspection and reference to generalized chart of characteristic

group frequencies 153

48

CHAPTER THREE

3.0 EXPERIMENTAL

3.1 Laboratory Apparati/ Equipment

(1) One litre 3-necked quick fit flask

(2) One litre sized electro heating mantle

(3) Fisher Johns melting point apparatus

(4) Reflux condensers

(5) Fractionating adaptors

(6) 3600C quick fit thermometer

(7) Gallenkamp mechanical stirrer

(8) EB 3A Vacum pump

(9) Dessicators

10. Seperatory and dropping funnels

11. Electronic metler balance

12. (Water bath) electric thermostated

13. IR spectrophotometer

14. Jenway 6405 Uv spectrophotometer

15. Jenway Conductivity meter

16. Wat-Horytont Electric stirrer

3.2: Reagents

Most of the reagents used were of analytical grade and were used without further

purification.

(1) 1-phenyl-3-methyl-pyrazolon-5-from Fluka

(2) Dioxane manufactured by Hopkins and Williams

49

(3) Anhydrous calcium hydroxide from BDH

(4) Calcium chloride from BDH

(5) Phosphorus pentachloride from BDH

(6) Acetyl chloride from sigma Aldrich

(7) Hexanoyl chloride from sigma Aldrich

(8) Benzoyl chloride form sigma Aldrich

(9) Butyryl chloride from sigma Aldrich

(10) Palmitoyl chloride from Fluka

(11) Magnesium acetate from Fluka

(13) Zinc acetate from Merck

(14) Copper Acetate, from Merck

(15) Cobalt (II) Chloride from Merck

(16) Hydrochloric acid Manufactured by sigma-Aldrich

(17) 95% ethanol from sigma-Aldrich

(18) Methanol from sigma-Aldrich

(20) N-Hexane manufactured BDH

(21) Acetone manufacture by Sigma-Aldrich

(22) Benzene manufactured by BDH

(23) Diethyl ether manufactured by BDH

50

(24) Dimethyl formaide (DMF) from Fluka

(25) Tetra hydro furan (THF) from East Anglia Chemicals

(26) Dimethylsulfoxide (DMSO) from BDH

3.30 Synthesis of 1-phenyl-3-methyl-4-acyl pyrazol-5-ones

3.31 Synthesis of 1-phenyl-3-methyl-4-Acetyl pyrazol-5-one (HPMAP)

The synthesis was carried out using a modified Jensen’s method11

. 8.5g 1-phenyl-3-

methyl-pyrazol-5-one (HPMP) was dissolved in 100cm3 of dioxane in a 1 litre three

necked flask fitted with an electric stirrer and a reflux condenser by warming. The

dioxane solution was allowed to cool to room temperature before 10g of Ca(OH)2 was

added and the mixture stirred, No heat was applied 3.5cm3 of acetyl chloride from a quick

fit dropping funnel was added dropwise within 3 minutes. The reaction was exothermic,

the reaction mixture was stirred for I hour without applying any heat and the resulting

orange mixture was then poured into a chilled 3M HCl (500cm3) solution with vigorous

stirring. The reaction mixture was later kept in a refrigerator until pinkish crystals

separated. They were filtered off, washed with water and recrystallized from aqueous

ethanol to give white crystals. The crystals were dried in air and stored in a desiccator.

3.32 Synthesis of 1-phenyl-3-methyl-4-Benzoyl pyrazol-5-one (HPMBP)

7.5g 1-phenyl-3-methyl-pyrazol-5-one (HPMP) was dissolved in 100cm3 of dioxane

in a I litre three necked flask fitted with an electric stirrer and a reflux condenser by

warming. The Dioxane solution was allowed to cool to room temperature before 10g of

Ca(OH)2 was added. The mixture was stirred with no application of heat before 5cm3 of

benzoyl chloride from a quick fit dropping funnel was added dropwise within 3 minutes.

The reaction mixture became a thick yellow paste and the temperature increased during

the first few minutes. Stirring of the mixture was continued with low heat application for

51

1 hour. The resulting orange mixture was poured into chilled 3M HCL (300cm3) with

stirring to decompose the calcium complex. Stirring was continued until an orange brown

solid precipitated from the solution. This was filtered off, washed with water and

recrystallized from aqueous ethanol to give white crystals.

3.33 Synthesis of 1-phenyl-3-methyl-4-Propionyl pyrazol-5-one (HPMPRP)

The synthesis was carried out as described above for HPMBP from 7.5g HPMP and

4cm3 of propionyl chloride.

3.34 Synthesis of 1-phenyl-3-methyl-4-Butyryl pyrazol-5-one (HPMBUP)

The synthesis was carried out as described for HPMBP from 8.5g of HPMP and

5.2cm3 of butyryl chloride.

3.35 :Synthesis of 1-phenyl-3-melthyl-4-Hexanoyl pyazol-5-one

The synthesis was carried out as described for HPMBP synthesis using 8.5g of HPMP

and 7cm3 of capyroyl chloride.

3.36:Synthesis of 1-phenyl-3-methyl-4-palmitoyl-pyazol-5-one (HPMPP)

The synthesis was carried out as described for HPMBP synthesis from 8.5g of HPMP

and 15cm3 of palmitoyl chloride.

3.40: Synthesis of metal-1-phenyl-3-methyl-4-acyl-pyrazolonates

3.41: Synthesis of 1-phenyl-3-methyl-4-actyl-5-pyrazolonato magnesium II Complex

Mg(PMAP)2. 2H2O

2.1623g 1-phenyl-3-methyl-4-acetyl-pyrazolone-5 (about10mM) was dissolved in

25ml 95% ethanol by warming at a temperature of 450C In a 100cm

3 beaker. This was

added to a solution of the magnesium (II) Acetate containing 5mM, 1.072g in 20cm3 of

52

distilled water drop wise with stirring until the complex precipitated out of solution.The

dirty white precipitate was filtered under suction and washed with aqueous ethanol (I/I),

dried in air and stored in a desiccator over fused calcium chloride. The method above was

used for the synthesis of 1-phenyl-3-methyl-4 butyryl pyrazolonato magnesium (II)

complex Mg(PMBUP)2 from 1.027g of 1-phenyl-3-methyl 4-butyryl pyrazolone and

2.144g of magnesium acetate Mg(CH3COO)2; for the synthesis of 1-phenyl 3-methyl-4-

Benzoyl pyrazolonato magnesium (II) complex, Mg(PMBP)2.2H2O from 2.783gof

HPMBP and 1.027g of Mg(CH3COO)2; for the synthesis of 1-phenyl 3-methyl-4-

propionyl pyrazolonato magnesium (II) complex dihydrate Mg (PMPRP)2 2H2O using

2.303g of HPMPRP and 1.027g of Mg (CH3COO)3; for the synthesis of 1-phenyl-3-

methyl-4-capyroyl-5-pyrazolonato magnesium (II) complex dihydrate from 2.723g of

HPMCP and 1.0217 of Mg(CH3COO)2 ; for the synthesis of 1-phenyl-3-methyl- 4-

palmitoyl-5-pyrazolonato magnesium(ii) dihydrate (Mg(PMPP)2.2H2O) from 4.126g of

HPMPP and 1.027g of Mg(CH3 COO)2.

3.42: Synthesis of 1-phenyl-3-methyl 4-acetyl-5-pyrazolonato copper (II) Complex.

2.163g(10mM) of 1-phenyl-3-methyl-4-acetyl-4-pyrazolone-5 was accurately

weighed and dissolved in 95% ethanol (50ml) and warmed to about 400C in a 100cm

3

beaker and 0.9082g(5mM) of copper(II) acetate was weighed and dissolved in 20Cm3

of

distilled water and added to the ethanolic solution of the ligand at 450C and stirred until a

dark green precipitate of Cu(PMAP)2 .2H2O was obtained. The precipitate was filtered

under suction, washed well with aqueous ethanol (1/1), dried in air before storing in a

desiccator over fused calcium chloride.

The method described above was used for the synthesis of 4-acyl-5-pyrazolonato

copper (II) complexes stated below. 1-phenyl-3-methyl 4-benzoyl-5-pyrazolonato copper

(II) complex Cu(PMBP)2 .2H2O was synthesized from 0.908g of Cu(CH3COO)2. 2H2O

53

and 2.783g of HPMBP, 1-phenyl-3-methyl 4-Butyryl 5-pyrazolonato copper (II) complex

Cu(PMBUP)2 2H2O was synthesized from 0.908g of Cu(CH3COO)2 and 2.443g of

HPMBUP, 1-phenyl-methyl-4-propionyl-5-pyrazolonato copper(II) complex

Cu(PMPRP)2 .2H2O synthesized from 0.908g of Cu(CH3COO)2 and 2.303g of

HPMPRP.1-phenyl -3-methyl-4-capyroyl pyrazolonato copper(II) complex dihydrate

(Cu(PMCP)2 .2H2O was synthesized from 0.908g Cu(CH3COO)2 and 2.723g of HPMCP;

1-phenyl-3-methyl-4-palmitoyl-5-pyrazolonato copper (II) complex dihydrate

Cu(PMPP)2.2H2O was synthesized from 0.908g of Cu(CH3COO)2 and 4.126g of HPMPP.

3.43: Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolonato cobalt (II) complex

1.189g (5mM) of cobalt (II) chloride was accurately weighed and dissolved in 75ml

95% ethanol with warming and slowly added with stirring to a hot ethanolic solution of

the ligand containing 2.163g (10mM) of 1-phenyl-3-methyl-4-acetyl pyrazolone in 75ml

of 95% ethanol. The pinkish orange precipitate formed was filtered under suction, washed

with aqueous ethanol (1/1), dried in air before storing in a desiccator over fused calcium

chloride.

The method described above was used for the synthesis of 1-phenyl-3-methyl-4-

benzoyl-5-pyrazolonato cobalt (II) Co(PMBP)2. 2H2O from 1.189g of Cobalt(II) chloride

and 2.7832g of HPMBP, 1-phenyl-3-methyl-4-Butyryl-5-pyrazolonato cobalt(II) complex

Co(PMBUP)2 2H2O from 0.595g of CoCl2 and 1.221g of HPMBUP, 1-phenyl-3-methyl-

4-propionyl -5-pyrazolonato cobalt (II) complex Co(PMPRP)2 .2H2O from 0.297g of

CoCl2 and 0.576g of HPMPRP, 1-phenyl-3-methyl-4-capyroyl-5-pyrazolonato cobalt (II)

complex Co(PMCP)2. 2H2O from 0.595g of CoCl2 and 1.362g of HPMCP, 1-phenyl-3-

methyl-4-palmitoyl-5-pyrazolonato cobalt (II) complex dihydrate Co(PMPP)2. 2H2O,

from 0.149g of CoCl2 and 0.516g of HPMPP.

54

3.44: Synthesis of 1-phenyl-3-methyl-4-Acetyl-5-pyrazolonato Zinc(II) complex.

1-phenyl-3-methyl-4-acetyl pyrazolone-5(1.082g) 10mM was accurately weighed and

dissolved in 50cm3 of 95% ethanol by warming at a temperature of 45

0C, this was added

with stirring to a solution of the Zinc metal containing 0.549g of Zn(CH3COO)2 in 20ml

of ethanolic solution. The solution was left to stand and a whitish precipitate separated

from the solution as the solution cooled. The precipitate was filtered in a sintered funnel

under suction and washed with water. The whitish product was air dried and stored in a

desiccator.

The method described above was used for the synthesis of 1-phenyl-3-methyl-4-Butyryl-

5-pyrazolonato Zinc (II) complex using 0.549g of Zinc Acetate and 1.221g of HPMBUP,

1-phenyl-3-methyl 4-Benzoyl-5-pyrazolonato Zinc (II) complex using 0.274g of Zinc

acetate (Zn(CH3COO)2) and 0.696g of HPMBP, 1-phenyl-3-methyl-4-propionyl-5-

pyrazolonato Zinc II complex (Zn(PMPRP)2 using 1.097g of Zn(CH3COO)2 and 2.303g

of HPMPRP, 1-phenyl-3-methyl-4-capyroyl-5-pyrazolonato Zinc (II) complex

Zn(PMCP)2 using 0.274g of Zn(CH3COO)2 and 2.723g of HPMCP and 1-phenyl-3-

methyl-4-palmitoyl-5-pyrazolonato Zinc (II) complex Zn(PMPP)2 .2H2O using 0.549g of

Zn(CH3COO)2 and 2.063g of HPMPP.

3.44 Preparation of 3M Hydrochloric acid solution

Fresh solutions of Hydrochloric acid used were prepared fortnightly. 3M

Hydrochloric acid solution was prepared by diluting 248.2cm3 of 37% HCl (sp.1.18) to

1000cm3 in a 1 litre volumetric flask with distilled deionized water. The volume of stock

acid diluted was obtained from the calculations below.

% purity of HCl=37%

Molecular weight of HCl=36.46gmol-1

55

Specific gravity= 1.18

Molarity of HCl= S.g x % purity x 1000

Molar mass or M W

= 1.19 X 0.37 X 100

36.46

Molarity of Conc HCl=12.08 mol dm-3

To prepare 1000cm3 of 3m HCl we used

C1V1=C2V2

C1=12.08moldm-3

C2=3moldm-3

V1=?

V2 = 1000cm3

V1 = (3 X 1000) Moldm-3

cm3

12.08 moldm-3

=248.2cm3

56

Fig 9.0: Reaction scheme for synthesis of a typical 4-acyl pyrazolone ligand and its

metal complex

N O

CH3

N

HPM P

ph

+

Ca(O H)2

N O

CH3

N

ph

O

Ca -H

N O

CH3

N

Calcium Com plex

C

H

Keto Form

N O

CH3

N

ph

C O H

enol form

N

CH3

N

ph

C O

O

M X H2O

M etal -4-Acyl pyrazolone

3M HCl

Reaction Schem e

O

ph

Ligand

R

R

R

Ligand

M (CH3CO O )

2.2H

2O

R-CoCl

R

57

3.50: PHYSICAL AND SPECTROSCOPIC STUDIES.

3.51: Melting point Determination. The melting points and dissociation temperatures

were determined using an electro thermal melting point apparatus with fine control.

3.52: Conductance Measurement

The molar conductance of each complex in DMF (Conc 10-3

M) measurements was

determined at 270C with the Jenway digital conductivity meter(model no J4500) using an

immersion type cell with a cell constant of 0.75.

3.53: Electronic Spectra Measurements

The electronic spectra of the ligands and complexes were obtained with a Jenway 6405

UV-visible spectrophometer coupled to a mecury computer monitor, in the department of

Pure and Industrial Chemistry ,University of Nigeria Nsukka

3.54: Infrared Spectra Measurement

The infrared spectra of the ligands and their Mg(II) Co(II), Cu(II) and Zn(II) complexes

were measured in the region of 4000-400cm-1

using the Perkin-Elmer fourier transform

infrared spectrometer ( model 2000) in the analytical and spectroscopic laboratory of the

department of chemistry, University of Waikato Newzealand.

58

CHAPTER FOUR

4.0 RESULTS AND DISCUSSION

4.10 Structure of ligands and complexes

Some 1-phenyl-3-methyl-4-acyl pyrazolone- 5 have been synthesized and the IR spectral

measurements (HPMAP,HPMBP,HPMBUP,HPMCP,HPMPRP,HPMPP,) showed that the

ligands may exist in four tautomeric forms as shown in figure 10.

CH3 C O

R

O

N

C6H

5

N

CH3 C O

R

O

N

C6H

5

N

O

C

RH

N

C6H

5

H

CH3

O

C

R

N

C6H

5

CH3

NH

O H

O

N

(a) (b)

(d)

Keto form s

Enol form s

(c)

Fig 10:Tautomeric forms of the ligand

R= HPMAP(1-phenyl-3-methyl-4-acetyl pyrazolone- 5), HPMBP(1-phenyl -3-methyl-4-

benzoyl pyrazolone-5) ,HPMBUP(1-phenyl-3-methyl-4-butyryl pyrazolone- 5), HPMCP(1-

phenyl-3-methyl-4-caproyl pyrazolone- 5),HPMPRP(1-phenyl-3-methyl-4-propionyl

pyrazolone- 5), HPMPP(1-phenyl-3-methyl-4-butyryl pyrazolone- 5).The results from

59

infrared spectral analysis showed that only three forms of the ligand were isolated from

aqueous ethanol and they are the forms in figures 10a, 10c and 10d above .The two enolic

tautomeric forms in 10c and 10d have been reported to be in resonace24

while the possibility

of an amino-diketo form of the ligand (10b) has been eliminated by the absence of bands

between 3100cm-1

-3500cm-1

in the anhydrous form of the ligand.

These tautomeric forms of the ligand have been found to behave as bidentate enols forming

neutral chelates of the type shown in figure 11 with Mg(II). Co(II), Cu(II) and Zn(II)

CH3

N

ph

OC

N O

M

ph

NO

O CH3

N

C

M = M g(II) or Co(II)

or Cu(II) or Zn(II) Ions.

R

R

Fig 11: Structure of metal complex.

60

4.20 Physical Data

Table 1 shows the physical data for the ligands while table 2 shows the physical data

for the Mg(II) Co(II) Cu(II) and Zn(II) complexes of the 4-acyl pyrazolones.

Table 1.0: Physical Data for the 4-acyl Pyrazolones

Molecular

formula

Molar

Mass

Colour Yield % Melting

Point 0C

C12H12N2

(HPMAP)

216.23

White

52

57-58

C17H1402

N2

(HPMBP)

278.32

White

85

115-117

C14H16O2N2

(HPMBUP)

244.29

Yellowish

brown

89

76-77

C16H20O2N2

(HPMCP)

272.35

Yellow

88

56-57

C13H14O2N2

(HPMPRP)

230.27

Yellow

75

61-62

C26H40O2N2

(HPMPP)

412.55 Bone

white

95 64-65

61

Table 2.0: Some Physical Data for Mg (11), Co (11), and Cu(11) and Zn(11) complexes

of some 1-phenyl-3-methyl 4-acyl pyrazolone-5.

Molecular Formular Molar Mass Colour Yield% M.P 0C

Mg C24H28O6N4

[Mg(PMAP)2.2H2O]

492.77 White 78.20 201-202

MgC34H32O6N4

[Mg(PMBUP)2.2H2O]

616.95 White 60.31 158-160

MgC28H36O6N4

[Mg(PMBP)2.2H2O]

548.89 Bone white 75.20 176-178

MgC32H44O6N4

[Mg(PMCP)2.2H2O]

605.85 Yellow 70.10 160-162

MgC26H32O6N4

[Mg(PMPRP)2.2H2O]

520.85 Yellow 55.09 182-183

MgC52H84O6N4

[Mg(PMPP)2.2H2O]

885.41 White 51.13 110-112

CoC24H28O6N4

[Co(PMAP)2.2H2O]

527.39 Pink 58.50 165-166

CoC34H32O6N4

[Co(PMBP)2 2H2O]

651.57

Pink

62.19

184-185

CoC28H36O6N4

[Co(PMBUP)2.2H2O]

583.47

Pink

50.01

145-147

CoC32H44O6N4

[Co(PMCP)2.2H2O]

639.63

Pink

72.69

137-328

CoC26H32O6N4

[Co(PMPRP)2.2H2O]

555.47

Deep pink

75.01

158-159

CoC52H84O6N4

[Co(PMPP)2.2H2O]

920.03

Pink

58.09

200-202

CuC24H28O6N4

[Cu(PMAP)2.2H2O]

532.00

Green

72.01

256-257

62

Molecular Formula Molar Mass Colour Yield % Melting point 0C

ZnC34H32O6N4

[Zn(PMBP)2.2H2O]

622.01

White

71.20

187-188

ZnC34H28O4N4

[Zn(PMBUP)2.]

553.95

Bone

White

62.10

144-145

ZnC32H44O6N4

Zn(PMCP)2

646.07

Yellowish

84.10

198-200

ZnC26H28O4N4

Zn(PMPRP)2

561.91

Yellow

58.13

169-170

ZnC52H80O4N4

[Zn(PMPP)2

890.47

Bone white

82.12

118-120

Molecular Fomular Molar Mass Colour Yield% M.P0C

CuC34H32O6N4

[Cu(PMBP)2.2H2O]

656.18

Green

60.56

269-270

CuC28H36O6N4

[Cu(PMBUP)2.2H2O]

588.12

Deep green

73.15

244-246

CuC32H44O6N4

[Cu(PMCP)2.2H2O]

644.24

Green

78.01

286-288

CuC26H32O6N4

[Cu(PMPRP)2.2H2O]

568.08

Green

67.12

294-296

CuC52H84O6N4

[Cu(PMPPP)2.2H2O]

924.64

Dirty green

70.09

244-250

ZnC24H28O6N4

[Zn(PMAP)2.2H2O]

533.83

White

86%

190-191

63

4.30: Conductivity Data

The molar conductance of 0.0001m solutions of the cobalt(II)copper(II) zinc(II) and 0.001m

magnesium(II)chelates in DMF at 27

0C are shown in tables 3a-d.The figures show that the

conductance values of all the complexes are negligible showing that all the cobalt(II),

copper(II) zinc and magnesium(II) complexes are neutral and non ionic.

Table 3a-3d: Conductivity Data for Mg (II), Co (II) Cu(II)and Zn complexes of 4-acyl pyrazolones.

Table 3a: Magnesium complexes

Complex Conc (mg/l) Molar Conductance (µohm-1m-1)

Mg (PMAP)2. 2H2O 0.012 8.6

Mg (PMPB)2. 2H2O 0.015 9.2

Mg (PMBUP)2. 2H2O 0.013 7.1

Mg (PMCP)2. 2H2O 0.012 8.3

Mg (PMPRP)2. 2H2O 0.01 3.8

Mg (PMPP)2. 2H2O 0.018 4.9

Table 3b Cobalt Complexes

Co (PMAP)2. 2H2O 0.01 4.8

Co (PMBP)2. 2H2O 0.013 6.9

Co (PMBUP)2. 2H2O 0.012 7.2

Co (PMCP)2. 2H2O 0.013 13.5

Co (PMPRP)2. 2H2O 0.011 2.7

Co (PMPP)2. 2H2O 0.018 15.1

Table 3c Copper Complexes

Cu (PMAP)2. 2H2O O.O1 21.5

Cu (PMBP)2. 2H2O 0.013 9.2

Cu (PMBUP)2. 2H2O 0.17 7.6

Cu (PMCP)2. 2H2O 0.007 23.6

Cu (PMPRP)2. 2H2O 0.028 12.9

Cu (PMPP)2. 2H2O 0.023 8.2

Table 3d: Zinc Complexes

Complex Conc (mg/l) Molar Conductivity ( µohm-1m-1)

Zn (PMAP)2. 2H2O 0.026 6.7

Zn (PMBP)2. 2H2O 0.012 1.6

Zn (PMBUP)2. 0.018 2.5

Zn (PMCP)2. 0.032 11.8

Zn (PMPRP)2. 0.028 0.72

Zn (PMPP)2. 0.022 2.5

64

4.40 Solubility Survey of Ligands and Complexes.

Tables 4a-4e show the solubility measurements for the ligands and their complexes in

various solvents. It was shown from table 4a that none of the ligand was soluble in water.

They were however soluble in most organic solvents.

Tables 4b-4e show that none of the metal complexes is soluble in water but have

varying solubility in various organic solvents. The magnesium (II) complexes show

solubility in most of the organic solvents, the cobalt (II) complexes also show varying degree

of solubility in the organic solvents, except the acetyl and palmitoyl complexes which were

insoluble in Diethyl ether and Acetone respectively. Also the Cu(II) and Zn (II) complexes

showed solubilities in most of the organic solvents with a few exceptions down the line.

Generally, it was observed that the complexes were hydrophobic. This reveals that the

distribution of these complexes from aqueous media into organic solvents such as

chloroform, Diethyl ether and CCl4, in which they are slightly soluble is favorable. The

complexes all showed remarkable solubility in DMF and DMSO, These two solvents have

lone pairs of electrons for donation, which probably completed the octahedron in the

complexes, thereby reducing further the ionic character of the complexes if any. These results

suggest that these two solvents could be efficient synergists in the extraction of Mg(II) Co(II)

Cu(II) and Zn(II) ions from aqueous media123

.

Table 4a solubility Data for the ligands

Solvent HPMAP HPMBP HPMBUP HPMCP HPMPRP HPMPP

Water i i I I i i

Ethanol S S S S S S

Methanol S S S S S S

Acetone VS VS VS VS VS VS

Dioxane VS VS VS VS VS VS

D. ether VS VS VS VS VS VS

T.H.F VS VS VS VS VS VS

CCL4 VS VS VS VS VS VS

n-hexane VS VS VS VS VS VS

Pyridine VS VS VS VS VS VS

Benzene VS VS VS VS VS VS

DMF VS VS VS VS VS VS

DMSO VS VS VS VS VS VS

65

Table 4b: solubility data for Magnesium (ii) complexes of the ligands

Solvent Mg

(PMAP)2.

.2H20

Mg

(PMBP)2

.2H20

Mg

(PMBUP)2

.2H20

Mg

(PMCP)2

.2H20

Mg

(PMPRP)2

.2H20

Mg (PMPP)2

.2H20

Water i i I I i I

Ethanol S S SP SP S S

Methanol SP SP SP I i I

Acetone VS VS S S SP SP

Dioxane VS S S S S SP

D. ether S S SP S S S

T.H.F VS VS S VS SP S

CCL4 S S SP S S S

n-hexane S SP I VS i i

Pyridine VS VS S S VS VS

Benzene SP SP I S SP SP

DMF VS VS VS VS VS VS

DMSO VS VS VS VS VS VS

Table 4c: solubility data for Cobalt (ii) complexes of the ligands

Solvent Co (PMAP)2

.2H20

Co (PMBP)2

.2H20

Co

(PMBUP)2

.2H20

Co (PMCP)2

.2H20

Co

(PMPRP)2

.2H20

Co (PMPP)2

.2H20

Water i i I I i i

Ethanol SP SP I I i i

Methanol SP SP I I SP i

Acetone SP SP SP I SP SP

Dioxane SP S S S S S

D. ether i VS SP S SP VS

T.H.F VS VS VS VS SP VS

CCL4 SP VS SP SP SP S

n-hexane i S SP SP S SP

Pyridine VS VS VS S VS VS

Benzene i S SP SP SP SP

DMF VS VS S VS VS VS

DMSO VS S S VS VS VS

Table 4d:solubility data for Copper(ii) complexes of the ligands

Solvent Cu (PMAP)2

.2H20

Cu (PMBP)2

.2H20

Cu

(PMBUP)2

.2H20

Cu (PMCP)2

.2H20

Cu

(PMPRP)2

.2H20

Cu (PMPP)2

.2H20

Water i i I I i i

Ethanol SP SP I I S i

Methanol SP SP I I S i

Acetone SP SP I SP VS i

Dioxane SP S SP SP SP SP

D. ether i SP SP SP VS SP

T.H.F S S S S VS S

CCL4 SP S SP S VS SP

n-hexane SP S SP SP SP i

Pyridine VS VS S SP VS S

Benzene i S I SP S i

DMF VS S VS VS VS VS

DMSO VS S VS VS VS VS

66

Table 4e:solubility data for Zinc(ii) complexes of the ligands

Solvent Zn (PMAP)2

.2H20

Zn (PMBP)2

.2H20

Zn

(PMBUP)2

Zn (PMCP)2

Zn

(PMPRP)2

Zn (PMPP)2

Water i i I I i i

Ethanol i i I SP i i

Methanol i i I SP i i

Acetone SP VS SP S SP i

Dioxane SP VS S S SP SP

D. ether i S S VS i SP

T.H.F i VS S VS VS S

CCL4 SP S SP VS SP SP

n-hexane SP SP SP SP SP SP

Pyridine SP VS VS VS VS S

Benzene SP S SP SP SP i

DMF SP VS VS VS VS S

DMSO SP VS VS VS SP S

Legend:i=insoluble,S=soluble,SP=sparingly soluble,VS=very soluble

4.50 Electronic spectra of ligands and complexes

Table 5a and 5b show the UV-visible spectral data for the ligands and their

magnesium(II), cobalt(II), copper(II) and Zn (II) complexes. Without the required quantum

mechanical calculations, assignment of the absorption bands to definite electronic transition

with complete certainty may not be possible, it is reasonable however to assign the bands

1 and

2 of the ligand anions to -*

transitions. From table 5b, it is evident that some of

the ligands suffered slight bathochromic shift in the 1

and 2

bands on chelation with the

metals and this agrees with previous observation. 64,79,157

Some hypsochromic shifts were

observed for the 1

and 2

bands of some other metal complexes of the ligand. This

observation is an exception to the general rule that there is always a bathochromic shift on

chelation to a metal atom shown by most 1,3 diketonates.64

Okafor 159

reported a similar

observation for rare earth trischelate of 4-acyl-pyrazolone. The 1

and 2

absorption bands

for the complexes are also due to intra ligand -*transitions. However the molar extinction

measured at identical wave lengths shows significant differences. It is pertinent to state that

the UV spectra of the complexes are similar in character to those of the free ligands,

indicating that the -bonding system in the free ligand is almost intact in the metal complex.

Thus only the orbital of the oxygen atom is substantially involved in -bonding with the

67

central metal. 20, 64, 123

The third absorption band 3

which appeared in the complexes of

cobalt (II), copper (II) and some of the Zinc(II) complexes of the ligands has been ascribed

to metal to ligand charge transfer. The molar absorptivity E which are mostly of the order of

103 supports this assertion

Table 5a: Electronic spectral Data of the Ligands

Ligand 1

max

(nm) E1(mol-1

cm-1

) 2

max

(nm) E2 (mol-1

cm-1

)

HPMAP 329.4 1.0 x104 359.4 5.9 X 10

4

HPMBP 321.8 3.0 x 103 354.2 5.4 x 10

4

HPMBUP 328.2 7.4 x 103 360.0 5.5 x 10

4

HPMCP 322.6 5.7 x 103 334.2 4.7 x 10

4

HPMPRP 327.4 9.6 x 103 360 5.8 x 10

3

HPMPP 321.8 4.6 x103 326 2.7 x 10

4

Table 5b: Electronic spectral Data of Mg(II) Co(II) Cu(II) and Zn(II) complexes of some 4-acyl pyrazol-5-

ones.

Complexes 1

Max (nm) E1(mol-1cm-1)

2 Max (nm)

E2(mol-1cm-1) 3

Max

(nm)

E3(mol-1cm-1)

Mg (PMAP)2. 2H2O 320.52 4.2 x 103 347.10 1.0 x 10

4

Mg (PMBP)2. 2H2O 331.60 9.6 x 103 334.50 2.4 x 10

3

Mg (PMBUP)2. 2H2O 329.2 6.2 x 103 355.00 3.8 x 10

4

Mg (PMCP)2. 2H2O 3276.6 5.1 x 103 363.60 1.7 x 10

4

Mg (PMPRP)2. 2H2O 328.5 3.6 x 103 365.12 3.0 x 10

4

Mg (PMPP)2. 2H2O 303.6 4.9 x 103 341.20 9.2 x 10

4

Co(PMAP)2. 2H2O 317.6 1.4 x 103 394.2 1.0 x 10

4 426 4.0 x 10

3

Co(PMBP)2. 2H2O 303. 6 1.1 x 104 356.8 2.1 x 10

3 476 8.5 x 10

3

Co(PMBUP)2. 2H2O 296 5.6 x 103 361.2 2.6 x 10

4 484.6 6.5 x 10

3

Co(PMCP)2. 2H2O 298 6.9 x 104 368 1.7 x 10

3 446 2.5 x 10

3

Co(PMPRP)2. 2H2O 314 1.43 x 104 343.6 3.6 x 10

4 497.8 2.1 x 10

3

Co(PMPP)2. 2H2O 293.4 3.2 x 103 364.2 9.0 x 10

3 502.4 3.0 x 10

3

Cu (PMAP)2. 2H2O 307.2 9.2 x 103 371.20 2.6 x 10

3 488.1 4.1 x 10

4

Cu (PMBP)2. 2H2O 298.2 8.4 x 103 362.10 1.6x 10

3 493.2 1.7 x 10

3

Cu (PMBUP)2. 2H2O 314.2 6.7 x 103 372.2 4.6 x 10

4 498.6 9.6 x 10

3

Cu (PMCP)2. 2H2O 293.2 2.8 x 103 360 3.0 x 10

4 495.2 1.0 x 10

4

Cu (PMPPP)2. 2H2O 308.2 4.2 x 103 353.2 3.2 x 10

4 499.4 1.0 x 10

3

Cu (PMPP)2. 2H2O 312.1 1.9 x 103 358.1 4.2 x 10

4 472 3.6 x 10

3

Zn (PMAP)2. 2H2O 322.6 3.7 x 103 326.2 3.2 x 10

4

Zn (PMBP)2. 2H2O 338.0 4.6 x 103 355.2 4.3 x 10

4

Zn (PMBUP)2. 322 3.1 x 103 332.2 5.6 x 10

4

Zn (PMCP)2. 322 4.2 x 104 372 3.5 x 10

4 497 4.5 x 10

3

Zn (PMPRP)2 321 4.3 x 103 376.2 2.6 x 10

3 493.2 3.0 x 10

3

Zn (PMPP)2 322 2.7 x 103 360 7.0 x 10

3 492 3.5 x 10

3

68

4.60 Infrared spectra of ligand and complexes

Reference was made to IR spectra of previous work done on 4-acylpyrazol -5-ones, 13,14,16-

20,25,37 In the assignment of the vibrational frequencies of the ligands and their Mg(II), Co (II)

Cu(II) and Zn(II) complexes. The IR spectral data (4000-400)cm-1

of the ligands and their

metal chelates with the possible assignment are given in tables 6a – 6f.

Table 6a: Infrared Frequencies of 1-phenyl-3-methyl -4-acetyl pyrazolone-5- one and

its Mg (ii), Cu(ii),Co(ii) and Zn(ii complexes.

HPMAP Co (PMAP)2 Cu (PMAP)2 Mg (PMAP)2 Zn (PMAP)2 Assignments

3468br 3573 sh 3468 br

3415 br 3574 sh v-O-HO-H2O

3341 br 3349br

3067 w 2985 w 3065 m 3065 w 2985 w Aryl –C-H

2991 w 2966 w 2965 w 3002 w 2957 w Saturated – C-H

2923 m 2920 m 2922 s 2926 w 2921 m vC-H

1639 vs - - - - v C=O

1623 vs 1606 s 1644 s 1623 vs vas C=O

1592 s 1594 vs 1592 s 1599 vs 1594 vs Phenyl ring VC=C

- 1582 m 1577 vs 1557 m 1588 s Pyrazole ring stretch

1535 s 1540 s - 1535 sh Pyrazole ring stretch

1500 m 1485 vs 1497 s 1512 br 1488 s vas C=C=C

1460 m - 1463 w 1472 w - Phenyl ring stretch

1440 m - 1442 m 1443 w - βas CH3

1399 sh 1404 w 1410 m 1416 w 1403 m Pyrazole ring stretch

1363 w 1375 vs 1380 s 1366 s 1375 vs vs C=O

1342 w - 1351 w 1343 w - βs CH3

1214 s 1214 m 1229 s 1214 w 1214 m vs C=C=C

1100 w 1156 w 1176 w 1184 w 1157 w βC-H

1161 s 1133 w - 1155 s 1133 w βC-H

1085 vs 1080 vs 1087 vs 1087 vs 1080 vs C-H In plane Deformation

1052 w 1055 w 1055 w - 1055 m C-H In plane

1027 s 1031 m 1031 s 1027 vs 1031 s Mono sub. Phenyl ring

1011 w 1014 m 1017 w 1019 s 1014 w CH3-rock out of plane

1001 w 998 w 999w 1001 w CH3-rock In plane

969 s 969 vs 974 vs 963 vs 968 vs C-C6H5 – stretch

909 s 914 s 907 s 906 s 914 s CH3 Stretch

834 m 844 s 848 s 848 s 844 -CH

750 vs 759 w 756 vs 761 vs 759 vs -CH

728 s 695 vs 749 m 749 sh Phenyl ringDeformation

690 vs 659 m 690 vs 691 m 696 vs Chelate ring Deformation

653 m 609 s 659 s 664 w 650 m Chelate ringDeformation

580 m 609 s 611 s 609 vs 608 vs Chelate ring vibration

507 s 510 s 513 s 510 m 509 vs Chelate ringVibration

- 448 s 477 m 493 s 447 m vM-O

- 404 w 414 m 424 w 404m Chelate ring Vibration

Legend = br=Broad, vs = very strong, S = strong, Sh sharp, W=weak Vw = very weak v=Sretching

frequency,β=bending or defomation,νas=Asymetric stretching,νs = Symetric stretching, =out of plane

bending

69

Table 6b:Infrared Frequencies of 1-phenyl-3-methyl 4-Benzoylpyrazol- 5-one and its

Co(ii), Cu(ii), Mg(ii) and Zn(ii) complexes HPMBP Co (PMBP)2 Cu (PMBP)2 Mg (PMBP)2 Zn (PMBP)2 Assignments

3467 br 3401 br 3448 br 3361 br 3342 br v-O-H-O H2O

3058 sh Aryl C-H

2924 sh 2926 sh - Saturated C-H

2852 sh - v-CH

2581 br - - - - v-O-H

1646 s - - - - vC=O enol

1604 s 1603 s 1626 s 1698 vs vas C=O

1597 w 1559 m 1592 w 1595 w 1528 sh Phenyl ring vC=C

1579 w - 1563 s - - Pyrazole rings stretch

1497 w 1499 s 1499 sh 1501 s 1482 w vC=C=C

1458

sh

1457 sh 1459 sh 1459 w - Phenyl ring stretch

- - 1441 s 1435 s 1433 s βas CH3

1400 s 1414 m 1423 w 1399 w 1399 s Pyrazole ring stretch

1348 s 1378 m 1380 vs 1359 s 1377w vs C=O

1310 m 1353 m 1354 m 1314 w - βs CH3

1221 m 1285 s 1245 w 1232 m 1244 vs vs C=C=C

1196 s 1192 m 1176 w 1177 w 1178 w β C-H

1182 w 1145 s 1162 s 1155 s 1159 s β C-H

1182 w 1110 m 1124 m 1133 s 1127 m Pyrazole ring breathing

1107

vs

1070 w 1072 m 1074 m 1074 w C-H Inplane deformation

1074 s 1021 m 1021 s 1026 sh 1020 s C-H In plane Mono sub

ph ring

992 m 1008 w 1001 w 1000 sh 1000 sh CH3 rocking

949 s 948 s 954 vs 949 vs 950 vs C-C6H5 stretch

932 vs 938 sh 934 w 919 w 926 w C-CH3 stretch

832 vs 831 s 843 s 841 vs 846 vs -CH

798 s 799 m 797 m 795 m 799 w -CH

706s 730 w 704 s 703 vs 701 s C-H out of plane

deformation of phenyl

ring

687 s 690 s 689 s 671 w 672 sh Chelate ring deformation

610 vs 601 s 613 sh 613 s 613 vs Chelate ring Vibration

534 s 539 s 567 s 552 m 552 s Chelate ring Vibration

493 s 504 s 518 s 508 s 508 vs Chelate ring Vibration

- 447 s 464 s 454 s 459 s v M-O

Legend = br=Broad, vs = very strong, S = strong, Sh sharp, W=weak Vw = very

weak v=Sretching frequency,β=bending or defomation,νas=Asymetric

stretching,νas = Symetric stretching, =out of plane bending

70

Table 6c: Infrared Frequencies Of 1-Phenyl-3-Methyl 4-ButyrylPyrazol-5-one and its

Co(ii), Cu(ii), Mg(ii) & Zn(ii) Complexes

HPMBUP Co (PMBUP)2 Cu

(PMBUP)2

Mg (PMBUP)2 ZN (PMBUP)2 Assignments

3470 br 3401 br 3468 br 3430 br - v-O-OH water

3065 w 3060 w 3062 w 3063 w 3060 w Aryl-C-H

2996 w 2957 s 2957 w 2957 s 2955 w Saturated C-H

2933 w 2931 w 2928 w 2932 s 2928 v-C-H

1617 s - - - - v C=O

1626 vs 1609 s 1643 vs 1615 s vas C=O

1597 sh 1592 w 1599 sh 1580 w Phenyl ring C=C

1562 s 1580 w 1577 vs 1582 vs 1534 s Pyrazole ring stretch

1499 sh 1509 vs 1500 vs 1512 s 1508 s vC=C=C

1461 s 1461 w 1462 w 1462 w 1462 w Phenyl ring stretch

1427 sh 1439 w 1442 s 1440 s 1439 s βas CH3

1392 s 1395 s 1383 vs 1396 s 1397 m vs C=O

1315 m 1324 m 1330 w 1324 s 1328 w βs CH3

1267 s 1265 w 1276 w 1274 w 1276 n vs C=C=C

1197 s 1195 m 1177 w 1196 w 1180 w β C-H

1154 w 1148 w 1157 m 1183 w 1180 w β C-H

1120 w 1105 w 1101 w 1107 w 1106 s C-H deformation in

plane

1097 m 1079 s 1078 vs 1080 vs 1079 vs C-H deformation in

plane

1077 w 1069 w 1062 s 1070 s - C-H Inplane deformation

of mono substituted ring

1063 w 1033 s 1035 s 1034 s 1032 s C-H Inplane deformation

of mono substituted ring

1032 s 1022 w 1020 w 1020 w 1022 w C-H deformationof mono

substituted ring

1001 s 1002 1003 s 1002 s 1003 s CH3 rocking

990 s - 990 s 993 s CH3 rocking

906 m 903 s 907 s 903 vs 904 vs C-C6H5 stretch

876 m 877 m 879 w 878 s 877 m C-CH3 stretch

783 s 804 w 808 s 807 m 205 w -C-H

756 vs 754 vs 760 vs 764 s 754 vs -C-H

691 vs 690 vs 690 vs 690 m 680vs Chelate ring deformation

684 w 665 m 659 s - 643 m Chelate ring deformation

642 m 644 w 640 sh 624 s 621 s Chelate ring deformation

607 m 616 s 614 sh - - Chelate ring vibration

500 s 508 s 510 s 506 vs 510 vs Chelate ring vibration

- 455 vs 489 vs 470 vs 467 vs vM –O

- 422 m 426 m 414 m vM–O

Legend = br=Broad, Vs = very strong, S = strong, Sh sharp, W=weak Vw = very weak

V=Sretching frequency,β=bending or defomation,νas=Asymetric stretching,νs = Symetric

stretching, =out of plane bending

71

Table 6d: Infrared frequencies of 1-phenyl-3-meltal 4-capyroylpyrazol-5-one and its

Co(ii), Cu(ii), Mg(ii) and Zn(ii) complexes

HPMCP Co (PMCP)2 Cu (PMCP)2 Mg (PMCP)2 Zn (PMCP)2 Assignments

3467 br 3392 br 3336 br 3428 br 3190 br v-O-HO-Water

- 3092 br 3058 m 3057 w 3054 w Aryl-C-H

2953 m 3056 w 2955 s 2954 s 2956 m Saturated C-H

2926 w 2953 s 2925 w 2939 m 2927 m v-C-H

1634 vs - - - - vC=O

- 1641 vs 1624 vs 1649 vs 1613 s vas C=O

1595 w 1595 m 1592 m 1598 s 1594 s Phenyl ring C=C

1562 s 1578 s 1577 s 1579 w 1578 w Pyrazole ring

stretch

1561 vs 1506 vs 1499 vs 1511 vs 1507 vs vC=C=C

1460 m 1456 m 1464 w 1476 w 1476 w Phenyl ring stretch

1443 w 1439 w 1441 s 1440 m 1441 s βas CH3

1363 w 1362 s 1377 vs 1363 vs 1370 vs vs C=O

1330 w 1324 s 1327 s 1324 s 1325 s βs CH3

1228 vs 1225 vs 1207 w 1225 m 1225 w vs C=C=C

1187 m 1187 w 1154 w 1192 w 1199 w β-C-H

1158 s 1154 s 1101 w 1154 m 1154 w β-C-H

1099 m 1078 vs 1079 vs 1080 vs 1079 vs C-H.inplane

deformation

1076 vs 1065 w 1064 s 1066 s 1066 s C-H.inplane

deformation

1031 s 1032 w 1032 s 1033 s 1033 s Mono subst ring def

1005 s 1012 s 1015 w 1013 s 1015 s CH3 rocking

- 998 s 999 s 999 s 998 s CH3 rocking

909 vs 903 vs 905 vs 902 s 904 s C-C6H5 stretch

855 m 846 s 849 vs 847 vs 850 vs C-CH3 stretch

827 w 800 w 805 s 802 m 801 w -CH

778 vs 767 s 768 w 789 m 768 w -CH

775 vs 755 vs 756 vs 755 vs 756 vs -CH

691 vs 689 vs 690 vs 689 vs 688 w Chelate

634 vs 663 w 662 s 662 s 668 w Ring

622 s 627 vs 623 s 621 vs Deformation

607 s 614 s 614 w 615 w - Chelate ring

507 vs 509 vs 511 sh 507 vs 511 vs Vibration

- 457 vs 495s 469 s 469vs vM-O

453 - 445 426 416 Chelate ring

vibration Legend = br=Broad, Vs = very strong, S = strong, Sh sharp, W=weak Vw = very weak

V=Sretching frequency,β=bending or defomation,νas=Asymetric stretching,νs = Symetric

stretching, =out of plane bending

72

Table 6e: Infrared Frequencies of 1-Phenyl-3- methyl -4-PropionylPyrazol-5-one and

its Co(11), Cu(11), Mg(11) and Zn(11) Complexes

HPMPRP CO (PMPRP)2 Cu (PMPRP) 2 Mg (PMPRP) 2 Zn (PMPRP) 2 Assignments.

3469br 3421 br 3468 br 3429 br – vO –HO

water

- 3061 W 3065Sh 3065w 3062Sh Aryl.C-H

2973M 2991W 2985m 2990Sh 2983W Saturated C-

H

2934W 2934M 2941Sh 2934S 2935Sh vC-H

1626S - - - - vC=O

1624Vs 1607Vs 1639Vs 1619Vs vas C=O

1572M 1597S 1574S 1599S 1595W Phenyl ring

vC=C

1527W 1544W 1538VS 1560W 1531W Pyrazole ring

stretch

1504Sh 1509VS 1497S 1513Vs 1509S vasC=C=C

1493W 1471W 1475Sh 1476S Phenyl ring

stretch

1444M 1440W 1440S 1441S 1442S βas CH3

1374W 1371W 1380S 1362S 1367S vs C=O

1332Sh 1325W 1328M 1325M 1327W βsCH3

1210M 1267W 1219M 1224W 1206W vs C=C=C

1183M 1196W 1180W 1196W 1183W βC-H

1160W 1147M 1127M 1148M 1045M βC-H

1084Vs 1079Vs 1079Vs 1081VS 1079Vs C-H inplane

Mono

Subititued

Phenyl Ring

1060W 1067W 1060W 1068W 1067Vs

1034M 1033S 1034S 1034S 1033S

1003S 1006Vs 1006Vs 1006Vs 1007 CH3 Rocking

963S 959S 962S 959Vs 960S C-C 6H5

Stretch

73

HPMPRP Co(PMPRP)2 Cu(PMPRP)2 Mg(PMPRP)2 Zn(PMPRP)2 Assignments

758S 816S 812VS 818Vs 815Vs -CH

740W 752VS 751VS 754VS 753Vs . -CH

689S 688S 690S 689Sh 688S Chelate ring

Deformation

639M 662M 659S 665W 658W Chelate ring

def

- 645W 641W 623W 642Sh Chelate ring

def

605M - - - - Chelate ring

vib

507S 507S 512M 503S 510Vs Chelate ring

vib

- 448S 497S 470S 459S v M-O

Legend = br=Broad, Vs = very strong, S = strong, Sh sharp, W=weak Vw = very weak

V=Sretching frequency,β=bending or defomation,νas=Asymetric stretching,νs= Symetric

stretching, =out of plane bending

74

Infrared vibrational frequencies of 1- Phenyl-3- methyl -4-Pamitoyl Pyrazolone and its Co(ii),

Cu(ii), Mg(ii) and Zn (ii)Complexes

HPMPP Co (PMPP)2 Cu (PMPP) 2 Mg (PMPP) 2 Zn (PMPP) 2 Assignments.

- 3401 br 3469 br 3433 br – vO –HO water

- - 3064 sh 3063 w Aryl C-H

2917s 2920w 2919 s 2921 s 2921s Saturated C-H

2849m 2853s 2851 s 2851 s 2850 s v-CH

2677Br - - - - v-OH-O

1627s - - - - vC = O

1646s 1626 m 1652 s 1614 s vas C =O

1594w 1595s 1591 s 1599 m 1596 sh Phenyl ring C=

C

1558m 1559s 1575 s 1580 w 1581 w Pyrazole ring

stretch

1500w 1501sh 1542 s 1513 s 1534 m vC= C=C

1472s 1473s 1563 m 146B m 1468 m Phenyl ring

stretch

1431m 1440 w 1441 m 1440 m 1441 w βas CH3

1348w 1394 m 1381 vs 1395 s 1371 vs vs C= O

1329w 1316 w 1327 w 1323 w 1328 w βs CH3

1228s 1217 m 1224 w 1217 w 1204 w Ѵ s C= C= C

1127s 1198 m 1198 m 1197 m 1145 w

β C-H

1122w 1178 w 1129 w 1170 w 1178w

1090s 1079 vs 1079 vs 1080 vs 1079 vs C-H In plane

Deformation 1079s 1067 w 1061 m 1068 m 1069 w

1063w 1034 m 1032 m 1034 s 1032 s C-H In Plane

def

1034w 1001 m 1001 s 1000 m 1001 s CH3 rocking

75

HPMPP Co(PMPP)2 Cu(PMPP)2 Mg(PMPP)2 Zn(PMPP)2 Assignments

1009w 905 w 985 s 980 vs 985 s CH3 rocking

940vs 912 m 905 m 912 m 908 m C-C6H5 Stretch

849w 847 w 846 m 847 m 847 m C-CH3 Stretch

782s 780 m 782 m 754 vs 752 vs

-CH 749m 749 s 752 vs 720 m -

688vs 689 s 689 vs 689 s 687 s Chelate ring

Deformation 640w 640 w 661 m 623 m 620 s

607s 607 w 532 w 532 w 509 s Chelate ring

vibration

547s 507 s 509 s 506 s 405 w

- 466 w 476 w 468 m 469 m vM-O

440m 416 m - - - Chelate ring

Vibration.

Legend = br=Broad, Vs = very strong, S = strong, Sh sharp, W=weak Vw = very weak

V=Sretching frequency,β=bending or defomation,νas=Asymetric stretching,νs Symetric

stretching, =out of plane bending.

The features of the IR spectra that are of most interest are outlined below.

(1) The presence of coordinated water in each of the Mg(II) Co(II) Cu(II) and some of the

Zn(II) chelates is indicated by the presence of broad peaks between 3100cm-1

and

3600cm-1

attributable to the OH stretching frequency of water.

(2) The intense bands centered at 2800cm-1

in the IR spectrum of some of the ligands

which has been attributed to asymmetric stretching frequencies of OH groups in enols

present in some of the ligands are absent in the spectra of all the metal complexes.

This indicates the participation of the OH in bonding.

76

(3) The shift of the νC=O stretching frequency of the ligands towards higher or lower

frequencies in their metal complexes, suggest that carbonyl groups are involved in

Chelation. The νC=O stretching frequencies of ligands and the asymmetric

frequencies of the metal chelates are shown in table 7.0.

(4) The absence of any peak between 3100cm-1

and 3600cm-1

in the anhydrous

complexes indicates the absence of ν-(NH-) and this eliminates the possibility of any

amino –diketo tautomeric form, reacting only through one or two of the carbonyl

groups or forming a coordinate link to the metal through the nitrogen atom of its

secondary amino group.

(5) The presence of bands between 400cm-1

and 500cm-1

typical of metal-oxygen

stretching frequencies of metal 1,3-diketonates suggests bonding through oxygen

atom 17, 25,37

. The exact vibrational frequencies assigned to the metal- oxygen bond

stretching frequencies are listed in table 7.0

The IR spectra of the ligands and their Mg(II), Co (II), Cu(II) and Zn (II) complexes

listed in tables 6a-6e above are divided into three main regions; 3600-1800cm-1

, 1800-

700cm-1

and 700-200cm-1

3600-1800cm-1

region

The most important feature of the chelate spectra of complexes in this region is the

presence of broad absorption bands in the IR spectra of the Mg(II), Co (II), Cu (II) and

some of the Zn (II) complexes which have been assigned to adduct water molecule

coordinated to the central metal ion or residing in the crystal lattice of the complexes.123

The absence of any peak between 3100cm-1

and 3600cm-1

in the anhydrous Zn (II)

complexes of the propionyl (Zn(PMPRP)2 Butyryl, (Zn(PMBUP)2) and palmitoyl

(Zn(PMPP)2 derivatives of the 4-acyl pyrazolone-5 clearly indicates the absence of

coordinated or crystal lattice water or solvent molecules. 28

. The presence of broad

absorption bands between 2000 and 2800cm-1

in the IR spectra of the Benzoyl (HPMBP)

77

and palmitoyl (HPMPP) derivatives of the 4-acyl pyrazol-5-ones which disappeared on

chelation has been ascribed to the presence of OH group of the enol form of the ligand

which was deprotonated on chelation with metal ion.

1800-700cm-1

region

This region contains bands derived from benzene, pyrazole and chelate ring

vibrations.These bands have been assigned by comparism with infrared spectral data

of the complexes of HPMBP 96

, HPMTFP 28,65

and HPMBUP 95

.The area of utmost

interest in this region are the C=O and C=C stretching frequencies (νas C=O and vas

C=C) of the chelate ring. These have been reported to be very sensitive to substitution

in -diketones 96

. The very intense bands located between 1600 and 1699cm-1

and

other strong bands observed between 1475cm-1

and 1540cm-1

in the spectra of the

chelates are attributed to νas C=O and vas C=C modes respectively. Table 7.0 shows

the observed νas C=O bands for all the metal chelates and it was observed that there is

a shift in the νC=O absorption bands to the νas C=O of the metal chelates.This

Suggests that the carbonyl group was involved in Chelation hence the formation of a

C=O-M bonding systems95

.Replacement of the methyl group of the acetyl moiety

with a phenyl group in the metal chelate shifts the C=O stretching bands to lower

frequencies. This suggests that there is a decrease in electron density around the C=O

bond, thus a decrease in the stability of the C=O bonding system.The stability order of

the νas C=O for the transition metals did not follow strictly the Irving Williams

stability order for transition metal complexes.(Cu > Ni > Co >Mn > Zn).

700-400cm-1

region

The metal-ligand vibrations below 700cm-1

are important because they

provide information on the strength of the M-O bonds and hence the stability of the

complexes. Metal isotopic substitution and normal coordinate analysis have shown

that pure M-O stretch (νas M-O) absorbs near 450cm-1

in acetylacetonates 96,159, 160

.

78

Table 7.0 shows the M-O stretching frequencies of some 1-phenyl-3-methyl-4-acyl

pyrazolone-5 and their metal chelates. The chelates were shown to have absorbed

between 439cm-1

and 497cm-1

indicative of M-O coordination. It was clearly shown

from the table that replacement of the methyl group of the acetyl moiety with a phenyl

group shifts the M-O stretching bands to lower frequencies. This is an indication that

the phenyl group substitution has caused a decrease in the electron density of the M-

O bond. Similar observation has been reported by Okafor96

. For the transition metal

chelates, the M-O stretching frequencies for all the 4-acyl substituents except the

Benzoyl followed the order Cu > Co > Zn, which conforms to the Irving Williams

stability order for transition metal complexes.

Table 7.0: Comparism of the vasC=O and vasM=O stretching frequencies of some

4-acyl pyrazolones and their divalent metal chelates.

vasC=O (cm-1

) vasM-O (cm-1

)

Compound Ligand Mg(II) Co(II)F Cu(II) Zn(II) Mg(II) Co(II) Cu(II) Zn(II)

HPMAP 1639 1644 1623 1606 1623 473 448 497 439

HPMPRP 1626 1639 1624 1607 1619 470 453 497 449

HPMBUP 1617 1643 1626 1609 1618 470 459 489 457

HPMCP 1634 1649 1634 1624 1613 469 471 485 469

HPMPP 1627 1652 1646 1626 1610 468 476 476 469

HPMBP 1646 1626 1604 1603 1698 454 447 464 459

79

4.70:The Effect of 4-acyl Substituents on the Infrared Carbonyl

Stretching Frequency of Metal (11) Chelates of some 1-Phenyl -3- Methyl

-4-acyl pyrazolones.

The infrared carbonyl stretching frequency of the metal(11) chelates are shown in table 7.0,

A close look at the data shows that for the 4-acetyl pyrazolone ligand, the order of stability

for transition metal chelates is as follows, Cu =Zn >Co which does not correspond to the

Irving Williams stability order for transition metal complexes.(Cu >Ni>Co>Mn>Zn). Similar

results were also observed for the transition metal chelates of HPMRP(Co >Zn >Cu),

HPMBUP(Co >Zn > Cu), HPMCP(Co > Cu > Zn), HPMPP (Co > Cu > Zn) and HPMBP

(Zn > Co > Cu) which does not equally follow the Irving Williams stability order for

transition metal complexes.28

In comparism with the infrared carbonyl stretching frequency, the metal-oxygen stretching

frequency of the transition metal chelates were also studied and the results shown in table 7.0

followed the trend HPMAP(Cu > Co >Zn), HPMPRP (Cu > Co > Zn), HPMBUP(Cu > Co >

Zn), HPMCP(Cu > Co > Zn), and HPMBP(Cu > Zn > Co). The above trend shows that the

infrared metal-oxygen stretching frequency for the transition metal chelates of all the 4-acyl

substituents except the Benzoyl derivatives followed closely the Irving Williams stability

order for transition metal complexes.28

Also looking at the data in table 7.0 down the

vertical axis, it will be noticed that there is a gradual change in the infrared carbonyl

stretching frequency of the metal chelates as the nature of the alkyl substituent at the 4-acyl

position changes, thus different correlation curves have been plotted for all metal chelates

showing the change in the infrared carbonyl stretching frequency as the molecular weight of

the substituent at the 4-acyl position increased.

Fig 12.0 shows the change in νC=O of the ligands as the molecular weight of the alkyl

substituent at the 4-acyl position increased. The curve shows that there is a noticeable change

in the infrared carbonyl stretching frequency with change in the alkyl substituent at the 4-

80

acyl position but in no particular order. Fig 13 shows some linearity with increase in the

length of the alkyl substituent at the 4-acyl position for the magnesium(11) chelates, with a

little deviation where the νasC=O for HPMPRP (1639cm-1

) is less than that for

HPMAP(1644cm-1

) which has a much lesser molecular weight. Figures 14 and 15 show the

plot of the νasC=O against the molecular weight of the alkyl substituents at the 4-acyl position

for the cobalt(11) and copper (11) chelates respectively. The two curves show that there is a

gradual increase in the νasC=O of the metal chelates as the length of the alkyl substituent at

the 4-acyl position increased, thus resulting in increased stability of the C=O bond .This

observation is as a result of increase in electron density around the C=O bond as the length

of alkyl substituent at the 4-acyl position increased.96

Plotted in figure 16 is νasC=O against

the molecular weight of the alkyl sustituents at the 4-acyl position for the Zinc chelates. The

curve shows that there was a gradual decrease in the value of the νasC=O as the molecular

weight of the alkyl substituent at the 4-acyl position increased, thus a decreased stability of

the C=O bonding system. The reason for this observation has not been completely established

but we ascribed it to be as a result of electronic and stearic interactions between the Zinc

metal ion and the pyrazole moiety.

81

82

The effect of the alkyl substituents at the 4-acyl position on the infrared metal-oxygen

stretching frequencies of the metal chelates was also studied using figures 17,18,19and 20

below. Figures 17 and 19 show the plots of the νasM-O against the molecular weight of the

alkyl substituents at the 4-acyl position for magnesium(11) and copper(11) chelates

respectively.

83

84

The nature of the two curves shows that there was a decrease in value of the νasM-O as the molecular

weight of the alkyl substituents at the 4-acyl position increased, thus a decrease in stability of the

metal-oxygen bond for both complexes. Figures 18 and 20 on the other hand show the plots of νasM-

O against the molecular weight of the alkyl substituent at the 4-acyl position for cobalt(11) and

zinc(11) chelates respectively. The plots show that there was a gradual increase in the metal-oxygen

stretching frequencies of the metal (11) chelates with increase in the molecular weight of the

substituent at the 4-acyl position ,resulting in increased stability of the M-O bond for the two metal

chelates. The reason for this observation has been attributed to increase in electron density around the

M-O bond with increase in the carbon chain length of the alkyl substituent at the 4-acyl position.

4.80 Conclusion

A combination of the data from UV spectra, IR and conductivity measurements shows

clearly that three different tautomeric forms of the ligand were synthesized and that

each of these ligands is behaving as a bidentate keto- enol forming neutral metal

chelates and bonding through the carbonyl oxygen and ,or that of the enolic

deprotonated hydroxyl group. The synthesis of the metal chelates with these ligands

gave quantitative yields, thus showing that these ligands are good gravimetric

reagents for magnesium, cobalt, copper and Zinc.

85

The data from the infrared spectral study of the metal chelates showed that the

carbonyl stretching frequency bands of the metal chelates increased as the length of

the carbon chain of the 4-acyl substituent increased for Magnesium (11),Cobalt (11),

and Copper (11) chelates This have been ascribed to the increase in electron density

around the C=O bond resulting in an increased bond stability and thus increase in the

carbonyl stretching frequencies of the metal chelates. A reverse trend was observed

for Zinc (11) chelates of the 4-acyl pyrazolones. Replacement of the alkyl group of

the 4-acyl substituent with the phenyl group resulted in a decrease in the carbonyl

stretching frequency bands for Mg(11),Co(11) and Cu(11) chelates ,which is as a

result of decrease in the stability of the C=O bond.

A comparative study of the infrared carbonyl and metal-oxygen stretching

frequencies of the transition metal chelates shown in table 7.0 revealed that the

νasC=O for the metal chelates did not follow the Irving Williams stability order for

transition metal complexes. While the νasM-O for the transition metal chelates of

HPMAP,HPMPRP, HPMCP,and HPMPP followed the order Cu > Co >Zn which

followed closely the Irving Williams stability order for transition metal complexes

while the νas M-O for the transition metal chelates of 4-Benzoyl pyrazolone

(HPMBP) followed the order Cu > Zn > Co which did not correspond to the Irving

Williams stability order for transition metal complexes.

86

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