High-pressure micro-Raman spectroscopic study of methyltrioxorhenium(VII)

Micro‐Raman spectra of methyltrioxorhenium(VII), CH3ReO3, were recorded at high external pressures, up to about 41 kbar, with the aid of a diamond‐anvil cell (DAC) in the presence and absence of paraffin oil (Nujol) as a pressure‐transmitting medium. The wavenumber vs external pressure plots display linear behavior up to 41 kbar, at which point sample decomposition occurs. In the case of the modes associated with the methyl group, the CH antisymmetric stretching modes are more sensitive to pressure (dν/dP = 0.88 and 1.04 cm−1 kbar−1) than the symmetric mode (dν/dP = 0.63 cm−1 kbar−1), and one branch of the split degenerate CH rocking mode exhibits a negative pressure dependence (−0.15 cm−1 kbar−1). The degeneracies of the ReO3 rocking and antisymmetric bending modes, located at 239 and 325 cm−1, respectively, at ambient pressure, are lifted in the crystal, and the resulting splitting increases as the pressure increases. The Re–C stretching vibration and one branch of the split degenerate ReO3 rocking modes are both particularly sensitive to pressure (dν/dP ≈ 0.96 cm−1 kbar−1). The dν/dP values for the ν(ReO) modes are significantly lower than those reported for other oxorhenium compounds. Copyright © 2006 John Wiley & Sons, Ltd.