Outer-sphere association of ions in DMSO solutions of nickel(II) salts

Abstract The visible absorption spectra and the molar conductance curves of solutions of NiI 2 , NiBr 2 , Ni(BF 4 ) 2 , Ni(ClO 4 ) 2 and Ni(CF 3 COO) 2 DMSO at 25°C have been determined. The results indicate a weak association which is only of the outer-sphere type, in each case involving the Ni(DMSO) 2 + 6 complex. The conductance data are analysed using the Lee-Wheaton conductance equation for unsymmetrical electrolytes. The first-step association constants ( K 1 ) and the limiting ionic conductances, λ 0 , for the Ni(DMSO) 2 + 6 cation as well as for the BF − 4 and CF 3 COO − anions are obtained. A linear relation between log K 1 and the reciprocal of the anionic radius is observed. On the basis of this relation, the relative contribution of the outer-sphere association for solutions of NiCl 2 in DMSO is estimated.