TERNARY COMPLEXES OF SOME LANTHANIDE IONS WITH CIS-1,2,3,4-CYCLOPENTANE TETRACARBOXYLIC ACID (CPTA) AS A PRIMARY LIGAND AND PYRIDINE-3-CARBOXYLIC ACID AS A SECONDARY LIGAND

Potentiometric studies are described for 1 : 1 : 1 ternary complex for mation of La3+, Sm3+, Dy3+ Gd3+, Yb3+ with cis- 1,2,3,4 cyclopentane t etracarboxylic acid (CPTA) as a primary ligand and pyridine-3-carboxyl ic acid (3-PCA) as a Secondary ligand at 25, 35 and 45 degrees C emplo ying modified method of Irving and Rossetti and keeping ionic strength mu = 0.2M (NaClO4). The studies show the formation of ternary complex es of the type M-CPTA-3-PCA where M = La3+ Sm3+, Dy3+ Gd3+, Yb3+. The values of stability constants show the order of stability in term of m etal ions as La3+ < Sm3+ < Gd3+ approximate to Dy3+ < Yb3+. The thermo dynamic parameters- changes in free energy (Delta G degrees), enthalpy (Delta H degrees) and entropy (Delta S degrees) have also been evalua ted.