Diffuse Reflectance Spectra of Some Thiometallates and Oxides of the Chromium Family

The visible and near-ultraviolet absorption spectra of NaCrS2, Cr2O3, (NH4)2MoS4, (NH4)2WS4, MoO3, and WO3 have been measured by diffuse reflectance methods. Peaks at 2.06 and 2.66 eV in Cr2O3 and 1.76 and 2.34 eV in NaCrS2 are interpreted as octahedral strong-field d3 4T2g and 4T1g transitions from the 4A2g ground state, consistent with Dq values of 0.206 and 0.176 eV and nephelauxetic ratios of approximately 0.48 each. Absorption edges in MoS42—, WS42—, MoO3, and WO3 are interpreted as charge transfer to localized MO's in the tetrahedral thiometallates, comparable to those observed in the chromate ion, and as charge transfer to delocalized bands in the oxides.