Short-range order in fused salts. I. Coordination states of nickel(II) in molten zinc chloride-potassium chloride mixtures

Absorption spectra of Ni(II) in molten KCl-ZnCl₂ mixtures have been obtained as a function of temperature and of melt composition in the range 4000-40,000 cm^-1. Spectra have been obtained over the entire composition range from pure liquid ZnCl₂ to pure liquid KCl. The extremes in the temperature range studied were 250 to 900°. Observed spectral changes have been interpreted to indicate the existence of (a) a two-species equilibrium involving Ni(II) in octahedral and distorted tetrahedral sites, and (b) transformation by a continuous distortion mechanism of an octahedral Ni(II) species to a highly distorted tetrahedral species. The effect of Cl^- polarization by Zn(II) and of volume changes on the coordination behavior of Ni(II) is discussed. A simple technique for handling and weighing small samples of highly hygroscopic materials is described.