Complex formation of some transition metals with thiazole Schiff bases

Proton-ligand stability constants of five Schiff bases, derived from 4-(p-bromophenyl)-2-aminothiazole and R substituted salicylaldehyde (R = H, 5-CH3, 4-CH3 and 5-Br) or 2-hydroxy-1-naphthaldehyde, and formation constants of their transition metal (Co-II, Ni-II, Cu-II and Zn-II) complexes have been determined pH-metrically at room temperature (25 degrees C) and at constant ionic strength, I = 0.1 M (NaClO4), in 75 : 25% (v/v) ethanol-water medium using Calvin-Bjerrum pH-technique as adopted by Irving-Rossotti. The order of stability constants of the complexes has been proposed, which is in accordance with the order suggested by Irving-Williams. The effect of elevated temperature (35 degrees C and 45 degrees C) on the determination of formation constants of metal complexes has been studied. Decrease in value of formation constant of the complex with increase in temperature indicates that low temperature is favorable for complex formation. The thermodynamic parameters (Delta G, Delta H and Delta S) at different temperatures have been calculated.