Absorption and magnetic circular dichroism spectra of Ru4+ in Cs2ZrCl6 and Cs2SnBr6

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Abstract
High resolution absorption and magnetic circular dichroism (M.C.D.) spectra are reported for Ru4+ (4d4) in the cubic hosts Cs2ZrCl6 and Cs2SnBr6. The spectra were recorded at liquid helium temperature over the ranges 16 000–26 000 cm-1 and 11 000–22 000 cm-1 respectively. All of the major features can be interpreted in terms of ligand-to-metal charge-transfer transitions. The results illustrate the need to use intermediate coupling in the 4d4 ground state, and a detailed analysis of the charge-transfer bands yields considerable information on the spin-orbit splittings of the ligand MO's and on the magnitude of metal-ligand electrostatic splittings. Excited state spin-orbit coupling is found to be much more important than metalligand electrostatic interactions. Comparisons are made with previous work on OsCl6 2- and OsBr6 2- (5d4).