Study of Thermodynamic Parameters and Thermodynamic stability of Quaternary Complexes of some rare earth metals

Abstract

    Investigation of potentiometric studies have been carried on complexation of lanthanides viz. La^(III) , Pr^(III), Nd^(III), Gd^(III) and Dy^(III) with N-hydroxyethyl ethylene diamine triacetic acid (HEDTA), Furan – 2 – carboxylic acid (FCA), thiophene – 2 – carboxylic acid (TCA), Pyridine – 2, 6 – dicarboxylic acid (PDA) and phthalic acid (PA). The stability constants of quaternary complexes and the dissociation constants of used ligands has been determined in aqueous solution at 40±1 c and at a fixed ionic strength (µ=0.1 M KNO₃). The relative order of stability has been observed to be La^(III) <Pr^(III)<Nd^(III)<Gd^(III) <Dy^(III) . The change in thermodynamic parameter (free energy change, G^o ) for the formation of 1:1:1:1 quaternary complexes has also been evaluated. The order of stabilization in the quaternary complexes has been explained on the basis of increasing value of ionic potential (ø = charge/radius ratio)

Keywords: N-Hydroxyethyl ethylene-diamine triacetic acid, pH- Metric Study, Stability of Quaternary complexes, Lanthanides