Potentiometric studies on stepwise biligand complex formation La(III), Pr(III) or Nd(III)-cyclo hexane-1, 2-diaminotetraacetic acid-hydroxy acid

Abstract

Potentiometric studies of the interaction between 1:1 Ln(III)-CDTA binary chelate (where Ln(III) = La(III), Pr(III) or Nd(III); CDTA = cyclohexane-1, 2-diamino-N,N,Nt́,N′-tetracetic acid) with certain hydroxy acids such as glycollic (GA), lactic (LA) and malic (MEA) are described. The nature of the titration curves indicates the stepwise addition of the secondary ligand to the initially formed 1:1, M(III)-CDTA binary complex. Formation constants ( K MAL) of the resulting biligand chelates have been determined at 30 ± 1° and 35 ± 1°C and also thermodynamic functions (viz, αG, ΔH and ΔS). The order of stability in terms of metal ions has been found to be La(III) < Pr(III) < Nd(III) and in terms of secondary ligand as MEA > LA > GA.