Abstract

Sangita sharma*, Dipika Dalwadi, Dhara Patel and Mahesh Kadia

The determination of formation constants of binary Lanthanone(III) complexes (ML), where M = Sm (III) or Eu (III) or Gd (III) or Tb (III) and L = 2-aminopyridine or 3-aminopyridine or 4-aminopyridine have been carried out using Irving – Rossotti titration technique in aqueous media at different temperatures and at ionic strength. To understand more about the nature of equilibrium involving lanthanide(III) complexes with aminopyridines the effect of dielectric constants on the stability of these complexes at different percentage of solvent variation and at different solvent systems has been studied.. The formation constant (logbn) have been calculated on IBM computer using BEST Program. The Smin values are also calculated. Thermodynamic parameters (DG, DH & DS) are also evaluated, negative DG & DH values and positive DS values indicate that complex formation is favorable at ordinary temperatures. Species distribution curves of complexes have been plotted as function of pH using Fortran IV program SPE PLOT to visualize the equilibria systems in pH range of 2-12 pH. The metal ligand formation constant values of selected aminopyridine were in the order 4-aminopyridine > 2-aminopyridine > 3-aminopyridine. The order of stability for metals is Sm < Eu < Gd < Tb. These orders can be explained on the basis of basicity of ligand, protonation of ligand, electronic configuration of metal ions, size and ionic potential of tripositive ion, charge/size ratio of metal ions and species distribution diagrams. The mechanism through which protonation and complex formation takes place have been also discussed and shown by chemical reactions.

Binary complexes; formation constant; aminopyridine; ionic strength

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