Bounds of Complex Formation for Alkali-Earth Cation in Molten Alkali Chlorides

Abstract The tendency of alkali-earth cation M 2+(M = Be, Mg, Ca, Sr, Ba) to form a complex ion in molten alkali chlorides ACl (A = Li, Na, K, Rb, Cs) has been interpreted in terms of attractive Coulomb interactions between the cation and anion; ΔΦ = Φ(MCl)– Φ(ACl). The experimental results by means of the Laser Raman spectroscopy indicated the presence of some complex ion in the molten ACl-MCl2 systems only when ΔΦ ≲ 0.38. Coexistence of an octahedral and a tetrahedral complex ions, [CaCl6]4- and [CaCl4]2-, has been suggested via deconvolution of Raman band in the molten 2KCl · CaCl2 composition.