ABSTRACT
Thermodynamic protonation constants of 5-aldehydosalicylic acid Schiff base with aniline and related compounds such as o-chloro aniline, o-nitro aniline, o-anisidine, o-toluidine and with 7-amino-4-methyl coumarin have been determined by Calvin-Bjerrum pH titration technique as used by Irving and Rosssotti. The solution stability constants of their complexes with bivalent metal ions Cu(II), Zn(II), Ni(II), Co(II), Cd(II) and Mg(II) with these ligands have been determined at four temperature in 50% water-ethanol mixture at an ionic strength of 0.1M (NaClO4). The order of solution stability constants was found to be Zn < Cu > Ni > Co = Cd > Mg which is in agreement with Irving – William’s order. The values of ΔGo, ΔHo, ΔSo have been calculated for the various complex equilibrium. The Copper chelates found to be more stable than Zn and Ni chelates due to difference in their configurations. Cu(II) forms square planar complex while Zn(II), Ni(II) form a tetrahedral or octahedral complex. The log K value for Zn chelate is found to be higher as compared to that of Ni chelate in case of above said all reagents used for investigation.