DETERMINATION OF THE MOLECULAR-STRUCTURES OF TUNGSTATES BY RAMAN-SPECTROSCOPY

An empirical correlation is developed for relating the wavenumbers of (W-O) stretching modes to W-O bond lengths and bond strengths for tungsten oxide reference compounds. A least-squares exponential fit of crystallographically determined W-O bond lengths to the wavenumbers of their Raman stretching modes is presented along with a relation between W-O bond strengths, in valence units, and wavenumbers of Raman stretching modes. The empirical band length/stretching mode wavenumber/bond strength relationships lead to a unique and effective method of interpreting Raman spectra of tungstate species, This method leads to the W-O bond lengths and coordination of the tungstate species. The utility of the method is illustrated by estimating the wavenumbers of the Raman stretching modes for the ideal WO4 tetrahedron and WO6 octahedron, and the bonds lengths and coordinations of the tungstate species in the reference compounds Na2WO4, PbWO4, CaWO4 and Bi2WO6. In addition, the W-O bond lengths of the WO6 octahedra in crystalline Ba2MgWO6 are reported for tbe first time. This new approach for evaluating tbe Raman spectra of tungstate species is expected to be generally applicable to all tungstates, regardless of environment, physical state, or oxidation state.