MIXED-LIGAND CHELATES OF N-PHOSPHONOMETHYL GLYCINE

The formation constants of 1:1 and 1:2 binary ([M-A] and [M-A(2)]) and 1:1:1 ternary metal chelates (EM-IP-LI or [M-L'-A], where A = N-phosp honomethyl glycine (NPMG), L = glycine (Gly) and P-alanine,(Ala), L' = 5-sulphosalicylic acid (5-SSA), oxalic acid (Oral, 1,10-phenanthrolin e (Phen), 2,2'-bipyridgl (Bipy) and iminodiacetic acid (imda) and M = Co-II, Ni-II: and Cu-II) have been determined potentiometrically in aq ueous medium at 20, 30, 40 and 50 degrees and at 0.10 M (KNO3) ionic s trength. NPMG behaves as a primary ligand in presence of N,O donors, G IS and Ala and as a secondary ligand in presence of O,O and N,N donors , 5-SSA, Oxa, Phen; Bipy and imda. The stepwise and overall 1 : It 1:2 and 1:1:1 stability constants, log K-1 (or:log K:), log K-2, log beta (2) log K-T, Or log K'(T) the differences in stability constants of 1: 1 secondary metal complexes and I:1:1 ternary systems (Delta log K or Delta log K'): the percentage of relative stabilisation values and per centages of distribution of various species have been evaluated and di scussed in terms of the basicity of ligands, statistical aspects, elec trostatic interaction, metal-ligand pi-interaction, denticity, nature of donor sites and stereochemical aspects. Thermodynamic parameters of the binary and ternary systems have been determined and discussed.