Stability constants and thermodynamic parameters of binary complexes of 2-hydroxy-1-4-napthoquinone monosemicarbazone (HNQS) with some lanthanons

Stability constants of the complexes of La(III), Pr(III), Nd(III), Sm(III) and Tb(III) with 2-hydroxy-1,4-naphthoquinone monosemicarbazone (HNQS) have been determined potentiometrically in 75% (v/v) aqueous dioxan medium at various ionic strengths and at different temperatures. The method of Bjerrum and Calvin, as modified by Irving and Rossotti, has been used to find out the values of n(overlined) and pL. The stability constants have been calculated using an IBM 360 FORTRAN IV computer by the weighted least squares method. The stability constants have also been calculated by Bjerrum half n(overlined) method. The order of the stability constants is found to be: La < Pr < Nd < Sm < Tb. Thermodynamic parameters, ΔG, ΔH and ΔS, have also been calculated. (author). 19 refs