Electronic Absorption and Voltammetric Analysis of Ni(II) Coordination in the Room Temperature Ionic Liquid 1-Ethyl-3-Methylimidizolium Chloride/Aluminum Chloride

摘要

The coordination chemistry of Ni(II) in the ionic liquid aluminum chloride : 1-ethyl-3-methyl imidazolium chloride (EMIC) has been determined using visible absorption spectrophotometry. By dissolving nickel chloride (NiCl_2) in Lewis acidic and basic ionic liquids and observing the resultant spectra and voltammetric information, one can determine the coordination and electron-transfer properties of Ni(II) at the various acidities. The optical data indicate the formation of tetrahedral NiCl_4~(2-) in the ionic liquid with excess EMIC (basic melt, N_(AlCl3) < 0.5) with absorption maxima at 659 and 707 nm. In acidic melts (N_(AlCl3) > 0.5), the wavelength of maximum absorbance shifts to 462 nm. This dramatic change in the visible spectrum is indicative of a change in the coordination of Ni(II) from tetrahedral (basic) to octahedral (acidic) geometry, changes which are mirrored in the cyclic voltammetry data of the same samples. Studies in the neutral melt are also presented here.