Studies on Thermodynamic and Formation Constants of Metal Complexes in Solution

DOI : http://dx.doi.org/10.13005/msri/060215

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The Proton ligand stability constants of 5-Aldehydosalicylic acid Schiff base with aniline and related compounds such as o-anisidine, m-anisidine and p-anisidine Schiff bases with 5-Aldehydo salicylic acid, and the stability constants of their complexes with bivalent metal ions Cu(II), Zn(II), Ni(II), Mg(II), Co(II) and Cd(II) have been determined employing Calvin Bjerrum titration technique as adopted by Irving and Rossotti in 50% (v/v) water alcohol medium at 15o, 25o, 35o, 45o ± 0.1oC, at an ionic strength of 0.1M (NaClO4). The order of stability constants was found to be Zn < Cu > Ni > Co ? Cd > Mg which is in agreement with Irving – Williams order of stability of bivalent metal complexes. The changes of colour during titration have been studied with related to stepwise formation constants of different complex species in solution. The log K values of the complexes were plotted against atomic number, ionic radii, electronegativity and ionization potentials of the metal ions. The formation constants were found to increase with the increase in the above periodic properties but decrease with increase in temperature. The values of DG, DH, DS have also been calculated for the various complex equilibria. The copper chelate is found to be relatively more stable than that of the Zn and Ni chelates due to the difference in their configurations. The former forms a square planar complex while the latter give a tetrahedral or octahedral complex. The log K value for Zn Chelate is found to be higher as compared to that of Ni in case of above said all reagents used for investigation.

Metal complexes; thermodynamic and formation cosntant