A Quantitative Approach to Stability Correlations of Some Lanthanide-Edta-Hydroxy Acid Ternary Complexes

Department of Chemistry, Dr. Harisingh Gour Vishwavidyalaya, Sagar-470 003

Manuscript received 16 March 1984, accepted IS August 1984

Metal-ligand stability constants of the mixed-ligand complexes of lanthanide metal ions, viz. La^III, Ce^III, Pr^llI, Nd^lll and Sm^III with edta as primary ligand and malic (ma), lactic (Ia), glycolic (ga), or gluconic (gluc) acid as secondary ligand have been determined\(\mathcal{p}\)H-metrically at 25° and ionic strength of 0.2 (mol dm^-3 NaCIO₄), using Irving· Rossotti titration technique. The ternary systems are of the type, M + A\(\rightleftharpoons\)MA, MA+L\(\rightleftharpoons\) MAL  The log \(K^{MA}_{MAL}\) values have been found tolie in the sequence La^III \(<\) Ce^III\(<\) Pr^III \(<\) Nd^III \(<\) Sm^III with respect to metal ions, and ma> la> ga> gluc with respect to the secondry ligands. The Δlog K value are negative due to electrostatic effects. Six log-log type stability correlations have been discussed with the help of mathematical equations derived for the purpose. It has been found that the plots of (i) log \(K^M_{ML}\) vs log \(K^H_{HL}\), (ii) log \(K^{MA}_{MAL}\) vs log\(K^H_{HL}\) (iii) log\(K^{MA}_{MAL}\) vs log \(K^M_{ML}\) (iv) log\(K^{MA}_{MAL}\)vs log \(K^{MA}_{MAL}\) (v) log \(K^{MA}_{MAL}\) vs log\(K^{MA}_{MAL}\) and (vi) log \(K^{MA}_{MAL}\) vs log \(K^{M'A}_{M'AL}\)· are all linear with non-unit slopes.