61

CHAPTER 2. EXPERIMENTAL

2.1. Materials

N-benzoyl glycine, 3-aminoacetophenone, 4-dimethylaminobenzaldehyde,

potassium hydroxide, potassium nitrate and metal salts, MCl2.nH2O (M = Ni, Cu

and Cd) were purchased from E-Merck. The surfactants used in this study, triton

x-100 (TX-100), sodium dodecyl benzene sulphonate (SDBS) and

cetyltrimethylammonium bromide (CTAB) were from Sigma-Aldrich and used as

obtained without any purification. Acetonitrile, benzene, ethanol, ether,

carbontetrachloride, 1,4-dioxane, N, N- dimethylformamide, dimethylsulfoxide,

tetrahydrofuran and all the other chemicals used in the study were of AnalaR

grade.

All the solutions used in potentiometric titrations were prepared in double distilled

water.

2.2. Physico-Chemical Techniques

Potentiometric titrations were carried out using a digital pH-meter of Eutech

Cyberscan pH 1100 with a glass calomel electrode at three different temperatures

(290.15, 300.15 and 310.15) K. The desired temperature for the titrations was

maintained using a thermostat model (D8-G Haake Mess-Techinik). The pH meter

was standardized before each titration with standard buffer solution of pH 4.00,

7.00 and 9.00 obtained from Eutech Instruments, Singapore.

Carbon, Hydrogen and Nitrogen were microanalyzed on Perkin-Elmer model

240C Analyzer. Molar conductances of the complexes were measured on a

62

Systronic Conductivitymeter 306. Magnetic susceptibility measurements were

carried out on a Magnetic Susceptibility Balance, Sherwood Scientific Cambridge,

UK while the variable temperature magnetic susceptibility was measured using

SQUID. Electron Spin Resonance spectra of Cu(II) complex at room and liquid

nitrogen temperature were obtained on a Varian E-line X band ESR Spectrometer

using DPPH as a g-marker. Electronic spectra of the complexes were taken on a

Shimadzu 2450 UV-Vis Spectrophotometer. Infrared Spectra of the ligands and

the complexes were obtained using a Shimadzu Fourier Transform Infrared

(FTIR) Spectrophotometer 8400S in KBr medium. 1H and

13C NMR Spectra were

recorded in DMSO-d6 on a Jeol AL 300 FT NMR Spectrometer. Mass Spectra

were obtained on a Jeol Sx102/Da-6000 Mass Spectrometer. The thermoanalytical

(TGA – DTA) measurements were carried out with Perkin Elmer Simultaneous

Thermal analyzer STA 6000.

2.3. Preparation and characterization of the ligands

2.3.1. Preparation of 4-dimethylamino benzylidene(N-benzoyl)glycyl

hydrazone (dabBzGH)

N-benzoyl glycine hydrazide was prepared as reported [1]. 4-dimethylamino

benzylidene (N-benzoyl)glycyl hydrazone, dabBzGH was prepared by refluxing

ethanolic solutions of N-benzoyl glycine hydrazide ( 0.02 M, 1.0 g, in 10 mL) and

4-dimethylamino benzaldehyde (0.02 M, 0.77 g, in 30 mL) for 4 hours. The light

yellow precipitate obtained on slow cooling of the reaction mixture was filtered,

washed repeatedly with ethanol, recrystallized from hot ethanol and dried at room

63

temperature. dabBzGH is characterized by its melting point, elemental and

hydrazine analysis, infrared, nuclear magnetic resonance and mass spectral data.

Yield = 60 %; m. p. 210 - 213°C; M+ peak at m/e = 324 as molecular ion peak in

the mass spectrum of the compound.

Figure 2.1. Structure of dabBzGH.

Scheme I. Mass fragmentation of dabBzGH.

NN

H HO

O

N

H

H

H

N

C H 3

C H 3

N

H HO

O+H

N+NH

H

N

C H 3

C H 3

N H

+CH 2O

N

C H 3

C H 3

O+

O+

NH

m /e ( 3 2 4 )

m / e ( 1 6 2 )

- C O

m / e ( 1 6 1 )

m /e ( 1 2 0 )m /e ( 1 3 4 )

m /e ( 1 0 5 )

m /e ( 7 7 )

m /e ( 1 1 9 )

- H C N + H 2

NN

O

H H

N(CH 3)2

N

O

HH

H12

3

4

1'2'

3'

4'

5'

6'

Figure 2.

Characterization of dabBzGH

Elemental and hydrazine analysis

66.96 (66.60); H, 6.20 (6.17); N, 16.97

IR (v, cm-1

). 1676 (amide

moiety, 1637 (amide I), 1529

1614 (CN), 952 (NN).

Figure 2.

Figure 2.2. Mass Spectrum of dabBzGH.

dabBzGH

hydrazine analysis: Found % (calcd %) for C18H24

(6.17); N, 16.97 (17.28); N2H4, 9.90 (9.80).

(amide I), 1554 (amide II), and 1471 (amide III) of hydrazidic

, 1529 (amide II), 1313 (amide III) of benzamide moiety,

Figure 2.3. IR spectrum of dabBzGH.

64

24N4O2. C,

of hydrazidic

of benzamide moiety,

1H NMR (dmso-d6), δδδδ (ppm):

7.25 – 7.74 (9H, multiplets, ring protons), 8.66, 8.47 (H, triplets, C

11.03 (H, singlet,-NNHCO).

Figure 2.

13C NMR (dmso-d6), ppm:

152.31 (12C, 8 singlets, ring carbons), 148.41 (

C6H5CONH-), 170.63 (singlet,

Figure 2.5

(ppm): 2.70 (3H, singlet, CH3), 7.90 (H, singlet,

7.74 (9H, multiplets, ring protons), 8.66, 8.47 (H, triplets, C6H5

NNHCO).

Figure 2.4. 1H NMR spectrum of dabBzGH.

), ppm: 40.07 (singlet, -CH3), 42.88 (singlet, -CH2), 112.63

152.31 (12C, 8 singlets, ring carbons), 148.41 (-NCH-), 167.48 (doublet,

170.63 (singlet, -NNHCO).

Figure 2.5. 13

C NMR spectrum of dabBzGH.

NN

O

H H

N(CH3)2

N

O

HH

H12

3

4

1'2'

3'

4'

5'

6'

65

), 7.90 (H, singlet, -NCH),

5CONH-),

), 112.63 –

), 167.48 (doublet,

66

2.3.2. Preparation of N-(2-2-[1-(3-aminophenyl)ethylidene]hydrazino-2-

oxoethyl) benzamide (aehb)

N-(2-2-[1-(3-aminophenyl)ethylidene]hydrazino-2-oxoethyl)benzamide, aehb

was prepared by refluxing ethanolic solutions of N-benzoyl glycine hydrazide

(0.02 M, 1.0 g in 30 mL) and 3-aminoacetophenone (0.02 M, 0.7 g in 10 mL) for

4 hours. The white precipitate obtained on slow cooling of the reaction mixture

was filtered and washed repeatedly with ethanol. It was then recrystallized from

hot ethanol and dried at room temperature. aehb is then characterized based on its

melting point, elemental and hydrazine analysis, infrared, nuclear magnetic

resonance and mass spectral data.

yield = 60 %; mp 213-215°C; M+ peak at 311 as the base peak in the mass

spectrum of the ligand.

Figure 2.6. Structure of aehb.

NN

O

H CH 3

N

O

HH NH 2

H

3'

5'

6' 4'

1'2'

12

3

4

Figure 2.7.

Scheme 2.

O

m /e ( 1 6 2 )

- C O

m /e ( 1 3 4 )

m /e ( 1 0 5 )

m /e ( 7 7 )

- H C N + H 2

O

N

HO

Figure 2.7. Mass Spectrum of aehb.

Scheme 2. Mass fragmentation of aehb.

N+NH

C H 3

N H

+CH 2

O+

O+

NH

m / e ( 3 1 0 )

m /e ( 1 6 2 )

- C O

m /e ( 1 4 8 )

m /e ( 1 1 9 )

NN

H H

O

NH

H

C H 3N H 2

H

O+H

m /e ( 9 3 )

67

N H 2

N H 2

68

Characterization of aehb

Elemental and hydrazine analysis: Found % (calcd %) for C17H18N4O2. C,

65.60 (65.80); H, 5.80 (5.80); N, 17.89 (18.06); N2H4, 10.40 (10.32).

IR (v, cm-1

). 1688 (amide I), 1577 (amide II), 1329 (amide III) of hydrazidic

moiety, 1634 (amide I), 1552 (amide II), 1311 (amide III) of benzamide moiety,

1597 (CN), 995 (NN).

Figure 2.8. IR Spectrum of aehb.

45060075090010501200135015001650180019502400270030003300360039001/cm

-20

-10

0

10

20

30

40

50

60

70

80

90

100

%T

3338.89

3188.44

3082.35

1687.77

1633.76

1597.11

1577.82

1552.75

1489.10

1456.30

1415.80 1

329.00

1271.13

1184.33

1124.54

995.30

910.43

887.28

837.13

632.67

597.95

532.37

509.22

462.93

420.50

P5

1H NMR (δ). 10.74, 10.92 (d, N

CH3), 4.77 (s, CH2), 5.44 (s, N

Figure 2.

13C NMR (ppm). 171.07 (s, >

benzamide), 41.37 (s, CH

(10 s, ring carbons).

Figure 2.

10.74, 10.92 (d, NHCO), 8.98, 9.14 (d, C6H5CONH), 2.50 (d, NC

), 5.44 (s, NH2), 6.93-8.22 (m, ring protons).

Figure 2.9. 1H NMR spectrum of aehb.

171.07 (s, >CO hydrazide), 166.82, 165.93 (d, >

H2), 148.55 (s, NC), 13.57, 14.24 (d, CH3), 111.45

Figure 2.10. 13

C NMR spectrum of aehb.

NN

O

H CH3

N

O

HH NH2

H

3'

5'

6' 4'

1'2'

12

3

4

69

), 2.50 (d, NC-

166.82, 165.93 (d, >CO

), 111.45-153.0

70

2.4. Preparation of the complexes

1 g of each ligand in 20 mL ethanol (3 mmol) was mixed with ethanolic

solutions of the metal chloride (MCl2.nH2O) (3 mmol). The reaction mixture was

then refluxed. Formation of the Cu(II) complex of dabBzGH occurred after

refluxing for 4 hours in ethanolic solution. The precipitate of Cu(II) complex was

separated out after cooling and filtered, washed with ethanol and dried in air.

However, Ni(II) and Cd(II) complexes could only be isolated after refluxing for ~

20 hours. The precipitation was also to be initiated by adding ~20 mL of

acetonitrile and THF to the concentrated reaction solution. The precipitates

obtained were filtered, washed with acetonitrile and THF mixture and dried in

desicator.

2.5. Analytical Procedures

The metal contents, after destroying the organic matter with concentrated

nitric acid followed by concentrated sulphuric acid, were estimated

gravimetrically using standard literature procedures [2]. Chlorine was estimated as

AgCl. Hydrazine was determined volumetrically by KIO3 method after subjecting

the ligand/complexes to acid hydrolysis with 6 N HCl for about 4 hours. Thermal

analysis data was carried out to determine the water content.

71

2.6. Potentiometric techniques

2.6.1. Preparation of reaction mixtures from the stock solutions

Preparation of stock solutions

Ligand solutions

The ligands taken for the study, dabBzGH and aehb were insoluble in water.

Therefore, the stock solutions of the ligands (0.01 M) for potentiometric titrations

were prepared by dissolving 0.324 g of dabBzGH and 0.310 g of aehb separately in

100 mL 40 % (v/v) aqueous - dioxane solution.

Metal ions solutions

Three transition metals viz, Copper, Nickel and Cadmium were chosen for the

present study. The metal solutions (0.01 M) for the potentiometric studies were

prepared by dissolving 0.4262 g of CuCl2.2H2O, 0.5943 g of NiCl2.6H2O and

0.5033 g of CdCl2.H2O in 250 mL double distilled water. All solutions were

standardized following the standard procedures [2].

Potassium hydroxide solution

A standard solution of carbonate free Potassium hydroxide solution (1.088 M)

was prepared in double distilled water and standardized with standard oxalic acid

solution (0.05 M) [2].

72

Nitric acid solution

A solution of Nitric acid (0.1 M) was prepared by diluting 1.619 mL of conc.

HNO3 to 250 mL with double distilled water. The acid solution was standardized

with a standard solution of KOH [2].

Potassium nitrate solution

A solution of Potassium nitrate, KNO3 (0.5 M) was prepared by dissolving

12.638 g of solid KNO3 in 250 mL of double distilled water.

Surfactant solutions

The surfactants taken for the potentiometric study in nonionic, anionic and

cationic micellar media were TX-100, SDBS and CTAB. The stock solution of the

surfactants (50 mM) were prepared by dissolving 3.1224 g of TX-100, 4.529 mL

of SDBS and 1.8225 g of CTAB each in 100 mL double distilled water.

Preparation of reaction mixtures

The following sets of reaction mixtures were prepared.

Solution (i) : [HNO3 + KNO3]

Solution (ii) : [solution (i) + Ligand], and

Solution (iii) : [solution (ii) + MCl2. nH2O] [M = Ni, Cu, Cd]

For each set of reaction mixture, three separate solutions (iii) containing

Ni(II), Cu(II) and Cd(II) ions were prepared. The metal to ligand ratio was kept

constant at 1:2 in all the reaction mixtures. The volume of each set was made up

to 25 mL with 40 % (v/v) aqueous - dioxane solution. The ionic strength of each

73

reaction mixture was maintained at 0.1 M using standard KNO3 solution as the

background electrolyte. The reaction mixtures were then titrated individually

against the standard KOH solution. All the titrations were carried out at three

different temperatures (290.15, 300.15 and 310.15) K.

For the titration in micellar media, TX-100, SDBS and CTAB were added

separately in each set of the above reaction mixtures before making up the

volume.

2.6.2. Calculation

Calculation of �� , �� and pL

The determination of stability constants of the metal complexes by pH-metric

titration method was developed by Bjerrum [3], Calvin and Wilson [4] and

modified by Irving and Rossotti [5]. The following relations were given to

calculate various parameters viz, n�H, � and pL to determine the stability constants

of the complexes.

��, the average number of protons bound to the ligand was calculated using

the relation (1).

0

0

0

)(

))((

LA

ALH

TVV

ENVVYn

+

+−−=

(1)

�, the average number of ligands attached per metal ion and pL, the free ligand

exponent were determined by the following expressions:

HMA

LM

nTVV

ENVVn

0

0

0

)(

))((

+

+−=

(2)

74

]

)log

1(

[log0

0

00

0

10V

VV

TnT

pHantiH

pL M

ML

jn

n

n

n +×

−=

∑=

=β

(3)

where Y is the number of dissociable protons present in the ligand. VL and VA are

the volumes of KOH consumed to reach a particular pH by solution (ii) and

solution (i), respectively, for the same pH reading and (VL - VA) measures the

displacement of the ligand curve with respect to the acid curve. V0 is the initial

volume of the reaction mixture (25 cm3), and E

0 and 0

LT are the resultant

concentrations of nitric acid and ligand in the reaction mixtures, respectively. 0

MT

is the metal ion concentration in solution (iii) while VM is the volume of alkali

added to solution (iii) to attain the pH reading as that of VA. βnH is the overall

protonation constant of the ligand.

Bjerrum’s half �� -value method

The proton - ligand and metal - ligand formation curves are obtained by

plotting the values of �� against pH and � against pL, respectively. The proton -

ligand and metal - ligand stability constants may then be evaluated from the

formation curves using Bjerrum’s half �-value method [3]. The proton - ligand

stability constants, log KnH are obtained from the ligand protonation curves by

taking the pH value corresponding to 0.5 �� value as the first stepwise

protonation constant, log K1H and the pH value corresponding to 1.5 �� as the

second stepwise protonation constant, log K2H and so on. The metal - ligand

stability constants, log Kn are evaluated from the metal - ligand formation curves

75

by reading out the values of pL which correspond to 0.5 � and 1.5 � as the first

and second stepwise metal - ligand stability constants, log K1 and log K2,

respectively, and so on.

Calculation of the thermodynamic parameter

The thermodynamic parameters, the overall change in free energy (∆G),

change in enthalpy (∆H) and change in entropy (∆S) were calculated by using the

temperature coefficients and Gibb’s Helmholtz equations [6].

Change in free energy (∆G) was calculated from the formation constant values

(log K) at various temperatures using the following equation:

∆G = -2.303RT log K (4)

where R (ideal gas constant) = 8.314 Jk-1

·mol-1

; K = Dissociation constant of

ligand or stability constant of the complexes; T = Absolute temperature.

Change in enthalpy (∆H) for the dissociation of ligand and complexation

process were evaluated from the slope of the plot (log K1H or log K vs 1/T) using

the graphical representation of Van’t Hoff’s equation (5) while the change in

entropy (∆S) could then be calculated using relationship (6).

∆G = ∆H – T∆S (5)

∆S = (∆H – ∆G)/T (6)

∆G values were calculated at different temperatures (290.15, 300.15 and

310.15) K where ∆H and ∆S were calculated at 300.15 K only.

76

References

1. T. R. Rao, Mamta Sahay and R. C. Aggarwal. Synthesis and characterisation

of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of acetone (N-

benzoyl)glycyl hydrazone, Indian J. Chem., 24A, 79-81 (1985).

2. A. I. Vogel, A Textbook of Quantitative Inorganic Analysis, 3rd

edn., Longman:

England, (1961).

3. J. Bjerrum. Metal ammine formation in aqueous solution. P. Hasse and Son:

Copenhagen, 63 (1941).

4. M. Calvin and K. W. Wilson. Stability of chelate compounds. J. Am. Chem.

Soc., 67, 2003-2007 (1945).

5. H. M. Irving and R. J. P. Williams. The stability of transition-metal complexes.

J. Chem. Soc., 3192–3210 (1953).

6. S. Glasston. Text book of physical chemistry. 2nd

edn., New York, (1974).