Dielectric Spectroscopy of Cesium Fluoride in Methanol

Abstract

Dielectric relaxation spectra have been measured at frequencies up to 20 GHz for CsF solutions in methanol (MeOH) at concentrations up to about 1 mol-L at 25°C. Spectra were also obtained for a few concentrations of the much less soluble KF. The data show that CsF forms a solvent shared ion pair (SSIP) in MeOH solutions. Detailed consideration of the possible geometries and comparison with earlier conductometric data suggest that the ion pair involves an oriented solvent molecule located at a vertex of one of the coordination sites of the cesium, rather than a conventional SSIP. Solvation numbers of the ions, estimated via the modified Cavell equation, are unrealistically large. This suggests, consistent with the large dielectric decrement and the conductivity data, that the ions significantly break down the chain structure of MeOH.