Specific Solvent Effects on the Complexation of Anions by Ligands

From conductimetrie measurements, the association constants K(A) of chlorides and nitrates in acetonitrile and of bromides in both acetonitrile and nitrobenzene were determined in the presence of various amounts of benzoic acids. From these data it was possible to determine the values of the complexation constants k(1)(-) between the ligands and the anions. In both solvents linear relationships exist between log k(1) 5nd the Hammett sigma parameters of the substituents. However, the values of both log k(1)(-) for the unsubstituted benzoic acid and the correlation factors (rho) are much lower in acetonitrile than in nitrobenzene. It is shown that this effect is due, to a large extent, to the complexation of the ligands by acetonitrile which competes with the ligandanion interaction. The rho factors for the three anions lie in the order of their basicity in water.