ELECTROCHEMICAL AND SPECTRAL INVESTIGATIONS OF NICKEL(II) ION EQUILIBRIA IN ROOM-TEMPERATURE CHLOROALUMINATE SOLVENTS

Absorption spectra have been recorded for NiCl2 dissolved in 0.8:1 and 1.5:1 molar ratio AlCl3-l-butylpyridinium chloride at room temperature. In basic (chloride-rich) melts, the Ni(II) is present as NiCl42-, with molar extinction coefficients a658=169 and a105=175 L mol-1 cm-1. 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 two-electron Nernst slope for Ni(II) additions in the acidic region and a fourth-power CI- ion dependence consistent with NiCl42- formation in the basic region. At 40 °C, the Ni(0)/Ni(II) standard electrode potential on the mole fraction scale was determined to be+0.800± 0.005 V (vs. a 2:1 A1 reference), and an equilibrium constant for the dissociation reaction NiCl42- Ni2++4C1-was determined to be (1.2 ± 1.0) × 10-46. © 1979, American Chemical Society. All rights reserved.