FORMATION STUDIES ON TERNARY AND QUATERNARY COMPLEXES OF SOME LANTHANIDES

The formation of 1 : 1 : 1, Ln(III)-PDA-NTA/FA ternary complexes and 1 : 1 : 1 : 1, Ln(III)-PDA-NTA-FA quaternary complexes, where Ln(III) = La, Pr and Nd; PDA = pyridine-2,6-dicarboxylic acid, NTA = nitrilotri acetic acid and FA = furan-2-carboxylic acid, has been studied potenti ometrically. The formation constants for the resulting ternary and qua ternary complexes have been evaluated at constant ionic strength (mu = 0.1 M KNO3) and temperature (28 +/- 1-degree). The order of stability constants in terms of metal ions have been found both in ternary and quaternary complexes as La(III)<Pr(III)<Nd(III), and this order has be en explained in terms of increased number of fused rings and coordinat ion number of the metal ions.