SYNTHESIS AND CHARACTERIZATION OF HYDRAZONE LIGANDS AND THEIR

METAL COMPLEXES

Coordination chemistry is a fascinating branch of inorganic chemistry.

The first successful preparation of the complex was carried out in centuries back.

There was a welcome renaissance in coordination chemistry after Werner, Werner’s theory has been extended greatly and is regarded as one of the milestones in the development of coordination chemistry.

In addition to the magnetic and spectral properties the stability of complexes were well explained by the crystal field theory developed by Van Vleck and bethe.

INTRODUCTION

Advance in the spectroscopic and crystallographic techniques, further fine tuned the understanding of this class of compounds.

It now provides new promising frontiers of research in supra molecular chemistry, non silicon based devices, single molecule based photonic device s and sensors.

Non silicon based devices, single molecule based molecular chemistry

We have chosen hydrazine based compounds, which contain two inter linked (>N-N<) nitrogen atom in their structure

Hydrazine readily react with carbonyl compounds to form compounds like hydrazone and hydralazone

Hydrazones contain the triatomic grouping [>C=N-N<] with an azomethine linkage

The two connected nitrogen atoms in these compounds are of different nature

The C=N bond is conjugated with the lone pair electron on the terminal nitrogen atom.

Hydralazones and phenyl hydrazones are some of the important group of compounds coming under nitrogen-oxygen donor ligands.

The presence of heterocyclic rings in Hydrazones can increase the number of binding sites and make them potential chelating ligands.

Also the ring can increases the denticity depending on its availability for coordination and other reaction condition.

The presence of an additional [>C=O] group increases the electron delocalization.

Many of the Aryl hydrazone complexes of transition metal ions are known to be effective model for elucidation of mechanism of enzyme inhibition.

2-thiophene carboxylaldehyde 2,3-butanedione

Hydralazine Phenylhydrazine

Many hydrazones were reported to show antimicrobial activities and anti-inflammatory activity.

Metal complexes of pyridylhydrazones have been used as acid base indicator.

Phenyl hydrazones were found to be good acid base indicators because of their ability to impart notable changes.

Some of the hydrazones are used as spot test reagents for certain transition metals.

Metal complexes of hydrazones are being used as luminescent probes and molecular sensors.

Hydrazones also find used as spectrofluorimetric reagents.

Pyridine 2-aldehyde p-nitro phenyl hydrazones as an indicator for the colorimetric pH measurements.

N, N, N hydrazones find use as metallochromic indicators.

A number of hydrazone complexes show remarkable catalytic activity.

Some hydrazones have also been used as herbicides, insecticides, nematocides, rodenticides, plant growth regulators as well as plasticizers and stabilizers for polymers.

Hydrazones are used as plasticizers and stabilizers for polymers and as polymerization initiators, antioxidants etc.

2-Hydroxy acetophenone aroyl hydrazone derivatives were found to inhibit corrosion of metals like copper.

Phenylhydrazone find application in qualitative and quantitative analysis and some find use as insecticide and herbicides.

Thiophenes are used as component of organic conducting polymers.

Thiophene ring systems occur in some plant products and are components of synthetic pharmaceuticals and dyestuffs.

Wide spectrum of applications and versatile modes of coordination of hydrazine based heterocyclic ligands inspired us to work on these compounds.

Scope of our work is the synthesis, characterization of a few hydrazine based heterocyclic ligands such as hydralazone and phenylhydrazone and also their metal complexes.

SCOPE AND OBJECTIVE OF THE WORK

So in this project, my aim is To synthesis the ligands: 2-

thiophenecarboxylaldehydehydralazone and 2,3-

butanedione phenylhydrazoneTo characterize the synthesized hydrazones

by different physiochemical techniques. To synthesis Cu (II), Zn (II) and Co (II)

complexes using the synthesized hydrazones as principal ligands.

Materials Required: Hydralazine 2-thiophene carboxylaldehyde Phenylhydrazine 2,3-butanedione Ethanol Cu (II) acetate Zn (II) acetate Co (II) acetate DMF DMSO Sodium acetate

MATERIALS AND METHODS

Elemental Analysis Micro analysis for carbon, hydrogen

and nitrogen in the synthesized hydrazones and their metal complexes were carried out an elemental model CHN analyzer at the sophisticated test and instrumentation centre STIC Cochin.

EXPERIMENTAL PROCEDURE

IR SpectroscopyThe IR spectroscopy is widely used as characterization techniques for metal complexes. The basic theory involved is that the stretching modes of ligands changes upon complexation due to weakening/strengthening of the bonds involved in the bond formation resulting in the subsequent changes in the position of the band in IR spectrum. The IR spectra of the components were recorded on a FTIR spectrometer using KBr pellets at STIC, Cochin.

• Electronic Spectroscopy:UV-Visible spectra of the ligand and complexes were

recorded using a Systronic-2210 UV-visible spectrophotometer in the 200-990 nm range, at the Department of Chemistry and Research Centre. Solvent used for recording the spectra of complexes was mainly ethanol.

• Conductivity studies:Molar conductance data were obtained using

Deluxe Conductivity Meter Model 601 E at the department of chemistry and research center. Conductivity of 10-3 M solution of the complexes in DMF was measured at room temperature.

PREPARATION OF 2-THIOPHENE CARBOXYLALDEHYDE HYDRALAZONE

(TL1)

To hydralazine(0.299g, 1.5m mol) dissolved in ethanol was added with stirring an ethanol solution of 2-thiophenecarboxylaldehyde (0.112g, 1m mol) and (1.5m mol) sodium acetate.

The mixture was stirred well with slight heating for 40 minutes when a yellow hydralazone precipitates out.

The precipitate was washed with water and then with water- ethanol mixture.

Synthesis of 2-thiophenecaboxylaldehydehydralazone ligand (TL1)

Then the precipitate was kept for some time.The ethanol was evaporated off.Yellow colored finely powdered 2-thiophene

carboxylaldehydehydralazone was obtained.Melting point was noted (Mp= 122 0C)

+ N

NH

N

N

S

2-thiophenecarboxylaldehyde hydralazone

An ethanol solution of Cu/ Zn acetate (0.5m mol) was added to an ethanol solution of (0.127g) 2-thiophene carboxylaldehydehydralazone .

Stirring continued with slight heating for 45-60 minutes.

When an olive green / yellow precipitate of the complexes are separated out for Cu/ Zn respectively.

The precipitate was washed with water and then with ethanol 2-3 times and dried.

 

Synthesis of complexes

An ethanol solution of Cobalt acetate (0.25m mol) was added to an ethanol solution of (0.127g) 2-thiophene carboxylaldehydehydralazone.

Stirring continued with slight heating for 90 minutes. When a dark brown precipitate of the complex was separated out.

The precipitate was washed with water and then with ethanol 2-3 times and dried.

Ligand / complex

Color C%

H% N% M%

TL1 Pale yellow

61.41 3.89 22.04 _

TL1C1 Brown 44.96 3.86 12.34 14.50TL1C2 Light

brown 43.06 4.20 11.82 12.40

TL1C3 Yellow 46.61 3.65 12.79 15.00

ELEMENTAL ANALYSIS

Solubility studiesSolubility of ligand and complexes were noted in

solvents like ethanol and DMF.Both ligand and complexes are soluble in DMF and

Partially soluble in ethanol Conductivity studies• Molar conductance of 10-3M solution of the

complexes in DMF was found less than 20 mhocm2mol-1.

• This indicates their non electrolytic nature. Cu (TL1)(OAC)2 , Co(TL1)(OAC)2(H2O)2, Zn(TL1)

(OAC)2.

Compound Conductance (mhocm2mol-1)Cu (II) complex 13Co (II) complex 18Zn (II) complex 14

Magnetic moment value of 1.7BM of the complex suggested distorted square planar geometry to Cu (II) complex.

Cobalt (II) complex showed a magnetic moment 4.8 corresponding to high spin octahedral geometries.

magnetic studies Compound Magnetic moment Cu (II) complex 1.7 Co (II) complex 4.8 Zn (II) complex _

IR spectra of the ligands and complexes were recorded using Brucker IFS66V IR spectrometer using KBr pellet method.

A sharp peak of medium intensity at 3319 cm-

1 in the IR spectrum of the ligand TL1 can be assigned to ν (N-H) stretching.

An intense sharp band at 1596 cm-1 for ν(C=N) and a band at 1078 cm-1 to ν(N-N) vibration.

Sharp and intense band at 705 cm-1 can be assigned to the C-H out-of-plane bending vibration.

IR SPECTRAL ANALYSIS

IR spectrum of TLI

In the spectra of the zinc complex, a broad band around 3207 cm-1 can be assigned to ν(N-H) stretching vibration.

The sharp and intense band due to C=N shifts downward by 1589 cm-1 indicating coordination through the azomethine nitrogen.

Band in the range 1280-1250 cm-1 in the complexes can be assigned to the symmetric ν(C-O) stretching vibration of coordinated acetate ion.

Weak band at 599 and 455cm-1 in the complexes can be assigned to the ν (M-O), ν (M-N) modes respectively.

IR spectra of Zinc complex

IR spectrum of TLIC3

Electronic spectra of the ligand indicate their hydrazone structure.

Absorption bands of TL1 were at 272 nm (π-π*) and 382 nm (n-π*).

Electronic spectral bands of the ligands corresponding to π-π* and n-π* has shifted in the complexes indicating coordination through azomethine nitrogen.

Electronic spectra of the complexes in the solid state were recorded and the main absorption obtained and the corresponding transition and geometries are determined.

The spectra of Cu (II) complexes showed bands at ~538 nm corresponding to 2B1g 2A1g transition in a square planar geometry.

ELECTRONIC SPECTRA

Uv-Visible spectrum of TLI

UV-VISIBLE SPECTRUM OF TLICI

The ligand has coordinated to the copper ion through azomethine nitrogen and one hetero nitrogen atom or acting as bidentate ligand .

Third and fourth coordination sites of the metal are occupied by acetate ion.

From CHN analysis and metal estimation, it is clear that only one molecule of ligand coordinated to the copper ion in the complex.

It is a four coordinated structure and the geometry may be square planar

CONCLUSION FOR TLI AND ITS Cu(II),Co(II) AND Zn(II) COMPLEXES

For the cobalt complex, the ligand coordinated to the metal through the azomethine nitrogen and one hetero nitrogen.

Thus the ligand act as a bidentate ligand. Two molecules of water and acetate ions also

coordinated with the central cobalt metal and form a six coordinated cobalt complex having octahedral geometry.

For the zinc complex, one molecule of ligand is coordinated to the central zinc ion through azomethine nitrogen and one hetero nitrogen.

Thus a four coordinated tetrahedral geometry is obtained.

STRUCTURE OF Cu(II), Zn(II) AND Co (II) COMPLEXES

Preparation of 2,3-butanedione phenylhydralazine

To phenyl hydralazine (0.24g) dissolved in ethanol was added with stirring an ethanol solution of 2,3-butanedione (0.086g, 1m mol) and sodium acetate.

Ligand was prepared by refluxing ethanol solution of phenyl hydrazine and 2,3-butanedione taken in 2:1 molar ratio.

The mixture was stirred well with slight heating for 90 minutes when a brown phenyl hydralazone precipitates out.

The precipitate was washed with water and then with water-ethanol mixture.

Synthesis of 2,3-butanedione phenylhydrazone

Then the precipitate was kept for some time.Then ethanol was evaporated off.Brown colored finely powdered 2,3-

butanedionephenylhydazone was obtained.Melting point was noted (mp= 168 o C).

2

phenylhydrazine + 2,3-butanedione 2,3-butanedionephenylhydrazone

HN N

HN N

0.5m mol of Cu(II)/ Zn (II) was dissolved in 10 ml of ethanol.

Then it was added drop by drop to 1m mol [0.26g] of 2,3-butanedione phenylhydrazone dissolved in 10ml of ethanol.

It was then mixed for 90 minutes using magnetic stirrer.

Brown/ white creamy complexes separated out of the solution.

Then it was filtered and washed with water containing ethanol and finally with ethanol

Synthesis of complexes

Ligand / complex

color C% H% N% M%

BPh Reddish brown

72.18 6.76 21.0 _

BPhCI brown 60.51 5.88 15.69 9.0BPhC2 Pale

yellow 60.36 5.86 9.27 9.27

Elemental analysis

Compound Conductance (mhocm2mol-1)

Cu (II) complex 150Zn (II) complex 145

Conductivity Studies

• From conductivity studies of the complexes in DMSO, the molar conductivity of the complexes were greater than 20 mhocm2mol-indicating their electrolytic in nature.• From elemental analysis and conductivity studies the following formula were proposed for the Cu(II) and Zn(II) complexes. [Cu (BPh)2 ](CH3COO)2 , [ Zn (BPh)2 ] (CH3COO)2.

IR spectrum of BPh , a sharp peak of medium intensity at 3344 cm-1 can be assigned to ν(N-H) stretching vibration.

An intense sharp band at 1596 cm-1 for ν(C=N) and a band at 1066 cm-1 to ν (N-N) vibration.

A weak band at 3025 cm-1 can be assigned to aromatic ν(C-H) stretching .

sharp intense bands at 687 and 745 cm-1 can be assigned to the aromatic C-H out-of-plane bending vibrations.

IR spectral analysis

IR spectrum of BPh

The sharp band of medium intensity at 3344 cm-1 in the ligand that can be assigned to ν(N-H), become broadened, increased in intensity and shifted to 3427 cm-

• In the acetate complexes also, there is broadening of this band which may be due to the H-bond formed between (N-H) hydrogen with the coordinated acetate groups.

• The ν(C=N) of the ligand is shifted to lower frequency indicating coordination through azomethine nitrogen.

• Bonding by the azomethine nitrogen is further corroborated by the upward shift of ν (N-N) in the ligand to 1100 cm-1 in complexes.

• Weak band at 546 and 490 cm-1 in the complex are assignable to the ν (M-N), ν(M-O) respectively

IR spectrum of copper complex

Electronic spectra of the complexes depend on energies of metal d-orbitals , their degeneracy and the number of electrons distributed in them.

These features are in turn controlled by the oxidation state of the metal, number and type of ligand and the geometry of the complexes.

So valuable information regarding the structure, geometry and the splitting of d-orbital can be obtained from their electronic spectra.

ELEMENTAL ANALYSIS

The spectra of BPh showed peaks at 300 nm and 351 nm which can be assigned to the π- π* and n-π* transitions.

Various analysis results indicate that the ligand BPhC1 has coordinated to the metal through both the azomethine nitrogen atoms.

from CHN analysis and metal estimation, it is clear that two molecules of the ligand coordinate to the copper ion in the complex.

Therefore it is a four coordinated structure and the geometry may be square planar

For zinc complex, two molecules of ligand coordinated to the central zinc through both the azomethine nitrogen atoms.

Thus a four coordinated square planar geometry is obtained.

Conclusion for 2,3-butanedione phenylhydrazone and its Cu(II), Zn (II) complexes

Structure of Cu(II) and Zinc (II) complexes of BPh

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