Potentiometric Studies on Some Ternary Complexes of Praseodymium(III) with Nitrilotriacetic Acid, N-Hydroxy- ethylethylenediaminetriacetic Acid and Ethylenediamine- tetraacetic Acid as Primary Ligands

Department of Chemistry, Nagpur University, Nagpur-10 Manuscript received 21 February 1976, revised 13 September 1977, accepted 21 March 1978 The formation constants of the ternary complexes of Praseodymium(III) with Nitrilotriacetic acid (NTA), N-Hydroxyethylethylenediaminetriacetic acid (HEDTA) and Ethylenediaminetetraacetic acid (EDTA) as primary ligands and Picolinic acid (PA) and Nitroso-R-salt (NRS) as secondary ligands have been investigated by potentio­metric titration technique. The values of formation constants of 1 : 1 : 1 ternary chelates are reported at three different temperatures and at fixed ionic strength, μ=0.2M (NaCIO4). Stepwise stoichiometric formation constants for the binary complexes of Pr(Ill) with PA and NRS have also been determined under identical conditions. The values of log \(K_{MAL}^{MA}\) have been found in the order, log \(K_{MAL}^{NTA}\)>log\(K_{MAL}^{HEDTA}\) >log \(K_{MAL}^{EDTA}\). Trends in the formation constants are discussed. The data also indicates that the Pr(III) ion expands its co-ordination number larger than six in some of these species