Experimental Determination Of Stability Constant And Thermodynamical Parameter Of Quaternary Complexes Of Some Lanthanides

Abstract

Quiternary complexes of some lanthanones viz, La^(III), Pr^(III), Nd^(III), Gd^(III) and Dy^(III) have been investigated potentiometrically with tripotassium salt of Ethylenediamine-N,N,N',N' - tetraacetic acid (K₃EDTA), Thiophene-2-carboxylic acid (TCA), Furan-2- Carboxylic acid (FA) and dibasic acid such as oxalic acid (ox), Succinic acid (SUC) in aqueous solution at 40±1°C and at an ionic strength of 0.1 mol dm^-3.' (KNO₃). The stability constants of these 1:1:1:1, quaternary complexes, have been evaluated by various computational methods. The relative order of stability in terms of La^(III) < Pr^(III) < Nd^(III) < Gd^(III) < Dy^(III) metal ion has been observed, which is almost in accordance with the increasing (F)=charge/radius ratio. The change in thermodynamic parameter (free energy change, DG°) has also been calculated under the same conditions.

Keywords :- Ethylene diamine tetracetic acid, Furan 2 –carboxylic acid, Lanthanides, stability constant, free energy change, potentiometric titration.