Vibrational Spectra of Molten Salts. III. Infrared and Raman Spectra of Variably Hydrated Zinc Nitrate

Abstract

Infrared and Raman spectra of liquids of composition Zn(NO₃)₂·xH₂O, with x having values from ∞ to 1.42, have been obtained. The changing forms of the spectra are reported as functions of both composition and temperature. The composition dependence shows that the nitrate ions become increasingly associated with zinc ions as the water content is decreased, until at very low water content no uncomplexed nitrate ions remain. Near‐anhydrous molten Zn(NO₃)₂ is thus shown to be a nonelectrolyte. All the results can be interpreted in terms of inner‐sphere coordinated water molecules being displaced by nitrate ions binding in a monodentate fashion. Below 4H₂O per Zn atom the coordination number of Zn must drop below six. The temperature dependence of spectra representing a wide range of compositions shows that different forms of nitrate perturbation caused by water and by zinc are distinguishable.