Vibrational spectra of some oxide halides of the transition elements with particular reference to gas-phase and single-crystal Raman spectroscopy

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Abstract
The following species have been examined in the Raman effect: (s = solid, l = melt, g = gas): VOCl3(g), VOF3(s), NbOCl3(g,s), MoO2Cl2(g,l,s), WO2Cl2(s), MoO2F2(s), WOCl4(g,s), MoOF4(l,s), WOF4(l,s), and OsO3F2(s). The results for the gaseous phase in all cases support the presence of principally monomeric species. In the solid state single-crystal Raman measurements on NbOCl3 suggest that the space group is P42nm not P42/mnm as suggested from X-ray diffraction studies. Single-crystal Raman data are also reported for WOCl4. In the case of the solid-state data a structure based on a six-co-ordinate central atom is satisfactory for NbOCl3(with an asymmetrical Nb–O–Nb bridge). For MoO2Cl2 a structure analogous to that of WO2Cl2 is satisfactory. MoO2F2 can be satisfactorily interpreted as based on eight-co-ordinate molybdenum with all atoms bridging. For MoOF4 and WOF4 it is suggested that the compounds are fluorine-bridged (in disagreement with results obtained from X-ray data for WOF4). For OsO3F2 the data are not inconsistent with six-co-ordinate osmium with cis-fluorine bridges, a terminal Os–F link and a C3v OsO3 residue. In the melt, MoO2Cl2 appears to be molecular while with MoOF4 and WOF4 there is evidence for terminal oxygen atoms, with presumably cis-fluorine bridges.

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