Comparison of the conductivity properties of the tetrabutylammonium salt of tetrakis(pentafluorophenyl)borate anion with those of traditional supporting electrolyte anions in nonaqueous solvents

Abstract

Cyclic voltammetry experiments at minielectrodes exhibit less ohmic error for lower polarity solvents when the supporting electrolyte anion is [B(C(6)F(5))(4)](-) rather than one of the smaller traditional anions such as [BF(4)](-), [PF(6)](-), or [ClO(4)](-). Conductance measurements have been performed for [NBu(4)][B(C(6)F(5))(4)] in tetrahydrofuran, dichloromethane, benzotrifluoride, and acetonitrile and compared with results for [NBu(4)](+) salts of several traditional anions in the same solvents. In solvents with dielectric constants of 10 or less, ion association constants, K(A), are as much as 2 orders of magnitude lower with [B(C(6)F(5))(4)](-), TFAB, as the electrolyte anion and the degree of this lowering is related to the acceptor property of the solvent. Analyses carried out on the basis of a Fuoss model attribute this fact to differences in concentrations of contact ion pairs rather than of solvent-separated ion pairs. The greater dissociation of the TFAB ion is attributed to its highly delocalized charge.