Crystal Spectrum of the Rare-Earth Hexahalide Complexes, MCl63−: The Absorption Spectrum of [(C6H5)3PH]3NdCl6

The site symmetry of Nd3+ in single-crystal [(C6H5)3PH]3NdCl6 is predicted by considerations of molar absorptivity, vibronic spectra, and stoichiometry. A calculation of the crystalline-field splitting of 4f3 J levels appears to predict a sixfold octahedral site symmetry with a slight distortion along one of the axes, in agreement with the observed spectrum. In addition, the observed spectrum indicates the occurrence of two slightly inequivalent sites of Nd3+. The effects of the small distortion away from octahedral symmetry and the spectrum due to two inequivalent sites are sufficiently small (5% of the average J-manifold crystalline-field splitting), however, as not to affect a first-order crystal-field analysis of the dominant portion of the spectrum. The crystal-field parameters based on octahedral symmetry, B4 = 282 cm−1 and B6 = 74.7 cm−1, predict a splitting of crystal quantum states in good agreement with experiment.