ELECTROCHEMICAL AND THERMODYNAMIC STUDIES OF THE ION-PAIR FORMATION OF CHLOROPENTAMMINECOBALT(III) ION IN ETHYL ALCOHOL-WATER MEDIA CONTAINING DIFFERENT DICARBOXYLATE LIGANDS

The ion-pair dissociation constants, K-D, of the ion-pair formed betwe en chloropentamminecobalt(III) ion (CpX2+) and a variety of dicarboxyl ate ligands, have been determined from EMF measurements of a cell comp osed of glass and calomel electrodes. Measurements were made in water and in aqueous binary mixtures of ethyl alcohol, over a wide range of solvent composition (0-60 wt% ethyl alcohol), at six different tempera tures (ranging from 30 to 55 degrees C at intervals of 5 degrees C). T he thermodynamic parameters of association Delta G(ass)(0), Delta H-as s(0) and Delta S-ass(0) have been calculated and discussed. Delta H-as s(0)-Delta S-ass(0), Delta S-ass(0)-Delta S-1(or 2)(0), Delta G(ass)(0 )-G(1(or 2))(0) and Delta H-ass(0)-Delta H-1(or 2)(0) correlations amo ng different solvent media and different dicarboxylate ligands were ex amined (where 1 and 2 denote the first and the second dissociation rea ctions of the studied dicarboxylic acids). The pK(D) value has been co rrelated with the dielectric constant of the medium according to Born' s equation. (C) 1998 Elsevier Science B.V.