Proton/Metal– Ligand Stability Constants of Complexes of N-Heterocycle

Substituted diethyl 4-(substituted-phenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5 dicarboxylate found to be effective as active biological compound.The physico-chemical properties of the transition metal complexes of these newly synthesized N-heterocyclics with certain metals are reported here. The proton–ligand and metal–ligand stability constants of complexes of diethyl 4-(substituted-phenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate with Ni(II), Cu(II), and Co(II) were determined in mixed solvents (70% dioxane). Presence of OH/NH group(s) in these compounds confirmed at 0.1 M ionic strength in 70% dioxane-water mixture pH-metrically. Ni(II), Cu(II), and Co(II) metal ions formed 1 : 1 and 1 : 2 complex with all the three ligands. The result shows that the ratio of logK1/logK2 is positive in all cases. This indicates that there is little or no steric hindrance to the addition of secondary molecules.