Solution equilibrium studies on complex formation by biological metal ions with 3- and 5- aldehydosalicylic acids and their aniline schiff base mixed ligands.

Equilibrium study on the mixed ligands complex formation of transition metal ions (M2+ = Cu, Zn, Ni, Co ) with 3-aldehydosalicylic acid (3ASA) and 5-aldehydosalicylic acid (5ASA) form variety of binary and mixed – ligand complexes with Cu(II), Zn(II), Ni(II) and Co(II). The mixed ligand complexes dominate the pH range of biological relevance. Formation constants of the proton-ligand and metal-ligand complexes at 30oC in 50% (v/v) water-ethanol medium, at ionic strength I= 0.1 mol/dm3, were determined employing Calvin Bjerrum titration technique as adopted by Irving and Rossotti. The order of stability constants were found and are in agreement with Irving-Williams order. The changes of colour during titration have been studied with related to stepwise formation constants of different complex species in solution for separate ligand titrations and mixed-ligand titrations. The complex formation equilibriums were elucidated by analyzing the speciation curves and correlated with the mode of coordination of the ligands.

Temperature effect on solution stability constants of metal complexes with schiff bases derived from 5-aldehydosalicylic acid – aniline and its related compounds.

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.

Role of temperature on stability constants of metal complexes in 50% (V/V) water-ethanol solution.

Thermodynamic protonation constants of 5-aldehydosalicylic acid-aniline Schiff base, [5ASAA], and o-, m-, p-Toluidine Schiff bases with 5-aldehydosalicylic acid have been determined by Calvin –Bjerrum pH titration technique as used by Irving and Rossotti. The thermodynamic formation constants of the chelates of Cu (II), Co (II), Ni (II), Zn (II), Cd (II) and Mg (II) with these four ligands have been determined at four different temperatures in 50% (v/v) water-ethanol mixture; the stabilities of complexes follow the Irving-William’s order.