Hydrothermal Raman microscopy studies of manganese carbonyls

We present here the application of Raman microscopy in providing simultaneous visual and spectroscopic characterisation of the physical and chemical changes occurring in organometallic materials while undergoing hydrothermal treatment. The effect of water at elevated pressures and temperatures on three prototype manganese carbonyls, Mn2(CO)10, (η5-C5H5)Mn(CO)3 and Mn(CO)5Br, was investigated. A Bassett-type hydrothermal diamond-anvil cell (HDAC) was used to subject each compound to conditions of at least 22.1 MPa and 374 °C (i.e., beyond the critical point of water), while Raman microscopy was used to monitor the structural changes occurring during the heating and cooling cycles of the cell. The hydrothermal studies showed that Mn2(CO)10, (η5-C5H5)Mn(CO)3 and Mn(CO)5Br dissolved in subcritical water at 150, 125 and 225 °C, respectively. Moreover, Mn(CO)5Br is also believed to have dimerized to Mn2(CO)8Br2 when the cell temperature was increased to 425 °C.