Resonance Raman, infra-red, and electronic spectral studies of the μ-oxo-decachlorodimetallate species, [Ru2OCl10]4-and [Re2OCl10]3-, and related ions

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Abstract
Studies of the resonance Raman spectra of the complexes K4[Ru2OCl10] and Cs3[Re2OCl10] have led in each case to the observation of, and identification of, six progressions at room temperature and eight at ca. 80 K, in all of which it is the ν1(a 1g ), symmetric metal-oxygen-metal (MOM) stretching mode which acts as the progression-forming mode. The longest progression in each case is the υ1ν1 one, which reaches υ1 = 12 (Ru) and 14 (Re). The enabling modes are other a 1g fundamentals or combination bands, except for certain cases in which the first and third overtones of infra-red-active fundamentals so act. The ν9(eu ), δ(MOM), mode is particularly effective in this respect, progressions υ1ν1 + 2ν9 and υ1ν1 + 4ν9 reaching to υ1 = 8 and 4 respectively (M = Ru), and 11 and 5 respectively (M = Re). The spectroscopic constants ω1, ω9, x 12, x 13, x 14, x 19, and x 99 have been determined in each case from the data. The symmetry force constant (F 11) associated with MO stretching, 5·60 and 6·84 × 102 N m-1 for Ru and Re respectively, is high and there is extensive mixing of the axial a 1g coordinates. The excitation profiles of all four a 1g fundamentals of each ion maximize near 20 000 cm-1 and, with Raman polarization data, this leads to the conclusion that the resonant electronic transition is an axially polarized π* ←π transition of the M-O-M π-bond system in each case.