The ionization of PCl6− in the solid state under pressure. II. Raman spectrum of phosphorus pentachloride III

The Raman spectrum of phosphorus pentachloride III, which is obtained by squeezing the ordinary phase II to a few kilobars (see preceding paper), has been recorded at ∼100 K and zero pressure. The ratio of the integrated intensities of the PCl4+ and PCl6− ions is much smaller in phase III than in phase II, showing that the ionization PCl6−→PCl4++2Cl− occurs in the solid at the transition. It appears to be the first example of a pressure-induced ionizing dissociation in a solid. Phase III is similar to, but apparently not identical with, a phase obtained by subliming phase II and condensing the vapor at, apparently, room temperature. The implications of this transformation for the synthesis of inorganic compounds is briefly discussed.