Comparative Study of Binary and Ternary Complexes of Some Rare Earths

Laxminarayan Institute of Technology, Nagpur University, Nagpur Manuscript received 21 February 1978, revised 25 July 1978, accepted 10 August 1978 Modified form of Irving and Rossotti's \(p\)H titration technique has been used to evaluate and compare the stability constants of the binary and ternary complexes of Sc(III), Y(III), La(III), Pr(III), Nd(III) and Sm(Ill) at 30° at an ionic strength of 0.2M NaClO4. For the study of ternary complexes, Nitrilotriacetic acid has been used as a primary ligand and polyhydroxy phenols, i.e., Pyrocatechol (PYC), Pyrogallol (PYG) and Gallic acid (GA) as secondary ligands. The stability constants of the binary complexes were found to be more than those of the corresponding ternary complexes which can reasonably be explained on the basis of electrostatic force between primary complex (metal in the case of binary complex) and secondary ligand, and space available to accommodate the secondary ligand. The stability decreases with the increase in ionic radii, i.e., Sc(III)>Y(III)>Sm(III)>Nd(III)>Pr(III)>La(III). In terms of secondary ligand, it follows the order PYC>GA>PYG. Rare earths form only 1 :1 binary complex, and 1 : 1 : 1 mixed ligand complex in all the cases