Comparative Study of Thermodynamic Parameters of Vanadium (IV) and (V) Acetohydroxamate Complexes

Abstract

Acetohydroxamic acid, CH_3CONHOH, forms highly stable complexes with vanadium (V) and vanadium (IV) in 1:1, 1:2 and 1:3 mole ratios. The stability of these complexes can be determined in terms of thermodynamic parameters; Delta G,Delta H and Delta S. The preliminary data, obtained through pH titration at various temperatures, was processed and analyzed by the computer program BEST for the refinement of graphically calculated log beta values. Graphs of lnbeta versus 1/T, gave a straight line, with a slope -Delta H/R and intercept Delta S/R. Enthalpy and free energy changes for V(V) complexes were found in the order of ML>ML_2>ML_3 with a negative sign. Whereas entropy change was found to be in the same order but positive, for vanadium (IV) acetohydroxamic acid complexes, the order of Delta G, Delta H and Delta S was ML>ML_3>ML_2. The Delta S is most positive for a 1:1 complex, while Delta G and Delta H are more negative for the same.