Electrochemical and spectral investigations of nickel(II) ion equilibriums in room-temperature chloroaluminate solvents

Abstract

Abstract : Absorption spectra have been recorded for Nicl2 dissolved in 0.8:1 and 1.5:1 molar ratio AlCl3:1-butylpyridinium chloride as a solvent at room temperature. In basic (chloride-rich) melts, the Ni(II) is present as NiCl42(-) with molar extinction coefficients a(658) = 169 and A(705) = 175 l/mol/cm. The reduction of the Ni(II) ion species at vitreous carbon electrodes exhibited irreversible behavior in acidic melts but no NiCl42(-) ion reduction was detected in the basic solvent. Potentiometry gave a theoretical 2-electron Nernst slope for Ni(II) additions in the acidic region and a fourth power Cl(-) ion dependence consistent with NiCl42(-) formation in the basic region. At 40 deg C, the Ni/Ni(II) standard electrode potential on the mole fraction scale was determined to be +0.8000 + or - 0.005 V (vs. 2:1 Al reference), and an equilibrium constant for the dissociation reaction, NiCl42(-) in equilibrium with Ni2(+) + 4 Cl(-) was determined to be 1.2 + or - 1.0 x 10 to the -46th power.