Conductometric study of complexation reactions between Benzyl bis semicarbazone and 3-Methylpyrazol-5-one with Cd+2 cation in pure and binary non-aqueous solvents

Semicarbazones are compounds which are synthesized by the condensation of semicarbazide and aldehydes/ketones ]1[. An interesting aspect is that the semicarbazones show a variety of coordination modes with transition metals ]2[. Pyrazolone is a five-membered lactam ring, containing two nitrogen and one ketonic group in its structure ]3[. In this paper, the complexation reactions between Cd+2 cation with benzyl bis semicarbazon (BSC) and 3-methylpyrazol-5-one (3-MP) ligands were studied in acetonitrile-ethylacetate (AN-EtOAc), acetonitrile-dimetylformamide (AN-DMF) and ethylacetate-dimethylformamide (EtOAc-DMF) binary mixtures at different temperatures using conductometric method. The results show that in all cases, the stoichiometry of the formed complexes is 1:1 (ML). The stability constants of the resulting complexes were calculated from the computer fitting of the molar conductance-mole ratio data at various temperatures. The selectivity order of Cd+2 cation for BSC and 3-MP ligands in most cases was found to be: (BSC.Cd) +2 (3-MP. Cd)+2. A nonlinear relationship was observed for changes of log Kf of complexes versus the composition of the binary mixed solvents. The values of standard thermodynamic quantities (ΔH˚C, ΔS˚C) for formation of (BSC.Cd) +2 and (3-MP. Cd)+2 complexes were obtained from temperature dependence of the formation constants using the van’t Hoff plots. The results show that the values and also the sign of these parameters are influenced by the nature and composition of the mixed solvents.