61 CAPTER 2. EXPERIMETAL 2.1. Materials -benzoyl glycine, 3-aminoacetophenone, 4-dimethylaminobenzaldehyde, potassium hydroxide, potassium nitrate and metal salts, MCl 2.n 2 (M = i, Cu and Cd) were purchased from E-Merck. The surfactants used in this study, triton x-1 (TX-1), 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,, - 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 p-meter of Eutech Cyberscan p 11 with a glass calomel electrode at three different temperatures (29.15, 3.15 and 31.15) K. The desired temperature for the titrations was maintained using a thermostat model (D8-G aake Mess-Techinik). The p meter was standardized before each titration with standard buffer solution of p 4., 7. and 9. obtained from Eutech Instruments, Singapore. Carbon, ydrogen and itrogen were microanalyzed on Perkin-Elmer model 24C Analyzer. Molar conductances of the complexes were measured on a
62 Systronic Conductivitymeter 36. 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 DPP as a g-marker. Electronic spectra of the complexes were taken on a Shimadzu 245 UV-Vis Spectrophotometer. Infrared Spectra of the ligands and the complexes were obtained using a Shimadzu Fourier Transform Infrared (FTIR) Spectrophotometer 84S in KBr medium. 1 and 13 C MR Spectra were recorded in DMS-d 6 on a Jeol AL 3 FT MR Spectrometer. Mass Spectra were obtained on a Jeol Sx12/Da-6 Mass Spectrometer. The thermoanalytical (TGA DTA) measurements were carried out with Perkin Elmer Simultaneous Thermal analyzer STA 6. 2.3. Preparation and characterization of the ligands 2.3.1. Preparation of 4-dimethylamino benzylidene(-benzoyl)glycyl hydrazone (dabbzg) -benzoyl glycine hydrazide was prepared as reported [1]. 4-dimethylamino benzylidene (-benzoyl)glycyl hydrazone, dabbzg was prepared by refluxing ethanolic solutions of -benzoyl glycine hydrazide (.2 M, 1. g, in 1 ml) and 4-dimethylamino benzaldehyde (.2 M,.77 g, in 3 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. dabbzg is characterized by its melting point, elemental and hydrazine analysis, infrared, nuclear magnetic resonance and mass spectral data. Yield = 6 %; m. p. 21-213 C; M + peak at m/e = 324 as molecular ion peak in the mass spectrum of the compound. 3 2 1 6' 1' 2' 5' 3' 4' (C 3 ) 2 4 Figure 2.1. Structure of dabbzg. m /e ( 3 2 4 ) C 3 C 3 + m / e ( 1 6 2 ) + m / e ( 1 6 1 ) C 3 C 3 - C + C 2 C 3 C 3 m /e ( 1 3 4 ) m /e ( 1 2 ) - C + 2 + + m /e ( 1 5 ) m /e ( 1 1 9 ) m /e ( 7 7 ) Scheme I. Mass fragmentation of dabbzg.
64 Figure 2.2. Mass Spectrum of dabbzg. Characterization of dabbzg Elemental and hydrazine analysis: Found % (calcd %) for C 18 24 4 2. C, 66.96 (66.6);, 6.2 (6.17);, 16.97 (17.28); 2 4, 9.9 (9.8). IR (v, cm -1 ). 1676 (amide I), 1554 (amide II), and 1471 (amide III) of hydrazidic moiety, 1637 (amide I), 1529 (amide II), 1313 (amide III) of benzamide moiety, 1614 (C), 952 (). Figure 2.3. IR spectrum of dabbzg.
65 1 MR (dmso-d 6 ), δ (ppm): 2.7 (3, singlet, C 3 ), 7.9 (, singlet, -C), 7.25 7.74 (9, multiplets, ring protons), 8.66, 8.47 (, triplets, C 6 5C-), 5 11.3 (, singlet,-c). Figure 2.4. 1 MR spectrum of dabbzg. 13 C MR (dmso-d 6 ), ppm: 4.7 (singlet, -C 3 ), 42.88 (singlet, -C 2 ), 112.63 152.31 (12C, 8 singlets, ring carbons), 148.41 (-C-), 167.48 (doublet, C 6 5 C-), 17.63 (singlet, -C). 3 2 1 6' 1' 2' 5' 3' 4' (C 3 ) 2 4 Figure 2.5. 13 C MR spectrum of dabbzg.
66 2.3.2. Preparation of -(2-2-[1-(3-aminophenyl)ethylidene]hydrazino-2- oxoethyl) benzamide (aehb) -(2-2-[1-(3-aminophenyl)ethylidene]hydrazino-2-oxoethyl)benzamide, aehb was prepared by refluxing ethanolic solutions of -benzoyl glycine hydrazide (.2 M, 1. g in 3 ml) and 3-aminoacetophenone (.2 M,.7 g in 1 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 = 6 %; mp 213-215 C; M + peak at 311 as the base peak in the mass spectrum of the ligand. C 3 1' 2' 3' 2 3 2 1 6' 4' 5' 4 Figure 2.6. Structure of aehb.
67 Figure 2.7. Mass Spectrum of aehb. m / e ( 3 1 ) C 3 2 + + C 3 2 m /e ( 1 6 2 ) m /e ( 1 4 8 ) - C + C 2 2 m /e ( 1 3 4 ) + m /e ( 9 3 ) - C + 2 + m /e ( 1 1 9 ) m /e ( 1 5 ) m /e ( 7 7 ) Scheme 2. Mass fragmentation of aehb.
68 Characterization of aehb Elemental and hydrazine analysis: Found % (calcd %) for C 17 18 4 2. C, 65.6 (65.8);, 5.8 (5.8);, 17.89 (18.6); 2 4, 1.4 (1.32). 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 (C), 995 (). 1 %T 9 8 7 6 5 4 1184.33 837.13 3 2 1-1 3338.89 3188.44 382.35 1687.77 1633.76 1597.11 1577.82 1552.75 1489.1 1456.3 1415.8 1329. 1271.13 1124.54 995.3 91.43 887.28 632.67 597.95 532.37 59.22 462.93 42.5-2 39 P5 36 33 3 27 24 195 18 165 15 135 12 15 9 75 6 45 1/cm Figure 2.8. IR Spectrum of aehb.
69 1 MR (δ). 1.74, 1.92 (d, C), 8.98, 9.14 (d, C 6 5 C), 2.5 (d, C- C 3 ), 4.77 (s, C 2 ), 5.444 (s, 2 ), 6.93-8.22 (m, ring protons). Figure 2.9. 1 MR spectrum of aehb. 13 C MR (ppm). 171.7 (s, >C hydrazide), 166.82, 165.93 (d, >C benzamide), 41.37 (s, C 2 ), 148.55 (s, C), 13.57, 14.24 (d, C 3 ), 111.45-153. (1 s, ring carbons). 3 2 C 3 1' 1 2' 3' 6' 4' 5' 2 4 Figure 2.1. 13 C MR spectrum of aehb.
7 2.4. Preparation of the complexes 1 g of each ligand in 2 ml ethanol (3 mmol) was mixed with ethanolic solutions of the metal chloride (MCl 2.n 2 ) (3 mmol). The reaction mixture was then refluxed. Formation of the Cu(II) complex of dabbzg 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. owever, i(ii) and Cd(II) complexes could only be isolated after refluxing for ~ 2 hours. The precipitation was also to be initiated by adding ~2 ml of acetonitrile and TF to the concentrated reaction solution. The precipitates obtained were filtered, washed with acetonitrile and TF 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. ydrazine was determined volumetrically by KI 3 method after subjecting the ligand/complexes to acid hydrolysis with 6 Cl 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, dabbzg and aehb were insoluble in water. Therefore, the stock solutions of the ligands (.1 M) for potentiometric titrations were prepared by dissolving.324 g of dabbzg and.31 g of aehb separately in 1 ml 4 % (v/v) aqueous - dioxane solution. Metal ions solutions Three transition metals viz, Copper, ickel and Cadmium were chosen for the present study. The metal solutions (.1 M) for the potentiometric studies were prepared by dissolving.4262 g of CuCl 2.2 2,.5943 g of icl 2.6 2 and.533 g of CdCl 2. 2 in 25 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 (1.88 M) was prepared in double distilled water and standardized with standard oxalic acid solution (.5 M) [2].
72 itric acid solution A solution of itric acid (.1 M) was prepared by diluting 1.619 ml of conc. 3 to 25 ml with double distilled water. The acid solution was standardized with a standard solution of K [2]. Potassium nitrate solution A solution of Potassium nitrate, K 3 (.5 M) was prepared by dissolving 12.638 g of solid K 3 in 25 ml of double distilled water. Surfactant solutions The surfactants taken for the potentiometric study in nonionic, anionic and cationic micellar media were TX-1, SDBS and CTAB. The stock solution of the surfactants (5 mm) were prepared by dissolving 3.1224 g of TX-1, 4.529 ml of SDBS and 1.8225 g of CTAB each in 1 ml double distilled water. Preparation of reaction mixtures The following sets of reaction mixtures were prepared. Solution (i) : [ 3 + K 3 ] Solution (ii) : [solution (i) + Ligand], and Solution (iii) : [solution (ii) + MCl 2. n 2 ] [M = i, Cu, Cd] For each set of reaction mixture, three separate solutions (iii) containing i(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 4 % (v/v) aqueous - dioxane solution. The ionic strength of each
73 reaction mixture was maintained at.1 M using standard K 3 solution as the background electrolyte. The reaction mixtures were then titrated individually against the standard K solution. All the titrations were carried out at three different temperatures (29.15, 3.15 and 31.15) K. For the titration in micellar media, TX-1, 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 p-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, 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). n ( VL VA)( + E ) = Y ( V + V ) T A L (1), the average number of ligands attached per metal ion and pl, the free ligand exponent were determined by the following expressions: ( V V )( + E ) M L n = ( V + VA) TM n (2)
74 n j 1 n = β ( ) n= n antilog p V + V pl = log1[ T nt V L M M ] (3) where Y is the number of dissociable protons present in the ligand. V L and V A are the volumes of K consumed to reach a particular p by solution (ii) and solution (i), respectively, for the same p reading and (V L - V A ) measures the displacement of the ligand curve with respect to the acid curve. V is the initial volume of the reaction mixture (25 cm 3 ), and E and T L are the resultant concentrations of nitric acid and ligand in the reaction mixtures, respectively. is the metal ion concentration in solution (iii) while V M is the volume of alkali added to solution (iii) to attain the p reading as that of V A. β n is the overall protonation constant of the ligand. T M Bjerrum s half -value method The proton - ligand and metal - ligand formation curves are obtained by plotting the values of against p 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 K n are obtained from the ligand protonation curves by taking the p value corresponding to.5 value as the first stepwise protonation constant, log K 1 and the p value corresponding to 1.5 as the second stepwise protonation constant, log K 2 and so on. The metal - ligand stability constants, log K n are evaluated from the metal - ligand formation curves
75 by reading out the values of pl which correspond to.5 and 1.5 as the first and second stepwise metal - ligand stability constants, log K 1 and log K 2, respectively, and so on. Calculation of the thermodynamic parameter The thermodynamic parameters, the overall change in free energy ( G), change in enthalpy ( ) and change in entropy ( S) were calculated by using the temperature coefficients and Gibb s elmholtz equations [6]. Change in free energy ( G) was calculated from the formation constant values (log K) at various temperatures using the following equation: G = -2.33RT 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 ( ) for the dissociation of ligand and complexation process were evaluated from the slope of the plot (log K 1 or log K vs 1/T) using the graphical representation of Van t off s equation (5) while the change in entropy ( S) could then be calculated using relationship (6). G = T S (5) S = ( G)/T (6) G values were calculated at different temperatures (29.15, 3.15 and 31.15) K where and S were calculated at 3.15 K only.
76 References 1. T. R. Rao, Mamta Sahay and R. C. Aggarwal. Synthesis and characterisation of Mn(II), Co(II), i(ii), Cu(II) and Zn(II) complexes of acetone (benzoyl)glycyl hydrazone, Indian J. Chem., 24A, 79-81 (1985). 2. A. I. Vogel, A Textbook of Quantitative Inorganic Analysis, 3 rd edn., Longman: England, (1961). 3. J. Bjerrum. Metal ammine formation in aqueous solution. P. asse and Son: Copenhagen, 63 (1941). 4. M. Calvin and K. W. Wilson. Stability of chelate compounds. J. Am. Chem. Soc., 67, 23-27 (1945). 5.. M. Irving and R. J. P. Williams. The stability of transition-metal complexes. J. Chem. Soc., 3192 321 (1953). 6. S. Glasston. Text book of physical chemistry. 2 nd edn., ew York, (1974).