Journal article
Raman Spectroscopic Study of Tungsten(VI) Oxosulfato Complexes in WO3−K2S2O7−K2SO4 Molten Mixtures: Stoichiometry, Vibrational Properties, and Molecular Structure
Department of Chemical Engineering, University of Patras and Institute of Chemical Engineering and High Temperature Chemical Processes (FORTH/ICE-HT), GR-26500 Patras, Greece1
Chemistry Department2
The dissolution reaction of WO3 in pure molten K2S2O7 and in molten K2S2O7−K2SO4 mixtures is studied under static equilibrium conditions in the XWO30 = 0−0.33 mol fraction range at temperatures up to 860 °C. High temperature Raman spectroscopy shows that the dissolution leads to formation of WVI oxosulfato complexes, and the spectral features are adequate for inferring the structural and vibrational properties of the complexes formed.
The band characteristics observed in the WO stretching region (band wavenumbers, intensities, and polarization characteristics) are consistent with a dioxo W(O)2 configuration as a core unit within the oxosulfato complexes formed. A quantitative exploitation of the relative Raman intensities in the binary WO3−K2S2O7 system allows the determination of the stoichiometric coefficient, n, of the complex formation reaction WO3 + nS2O72− → C2n−.
It is found that n = 1; therefore, the reaction WO3 + S2O72− → WO2(SO4)22− with six-fold W coordination is proposed as fully consistent with the observed Raman features. The effects of the incremental dissolution and presence of K2SO4 in WO3−K2S2O7 melts point to a WO3·K2S2O7·K2SO4 stoichiometry and a corresponding complex formation reaction in the ternary molten WO3−K2S2O7−K2SO4 system according to WO3 + S2O72− + SO42− → WO2(SO4)34−.
The coordination sphere of W in WO2(SO4)22− (binary system) is completed with two oxide ligands and two chelating sulfate groups. A dimeric [{WO2(SO4)2}2(μ-SO4)2]8− configuration is proposed for the W oxosulfato complex in the ternary system, generated from inversion symmetry of a WO2(SO4)34− moiety resulting in two bridging sulfates.
The most characteristic Raman bands for the WVI oxosulfato complexes pertain to W(O)2 stretching modes (i) at 972 (polarized) and 937 (depolarized) cm−1 for the vs and vas W(O)2 modes of WO2(SO4)22−, and (ii) at 933 (polarized) and 909 (depolarized) cm−1 for the respective modes of [{WO2(SO4)2}2(μ-SO4)2]8−.
Language: | English |
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Publisher: | American Chemical Society |
Year: | 2011 |
Pages: | 4214-4222 |
ISSN: | 15205215 and 10895639 |
Types: | Journal article |
DOI: | 10.1021/jp109339g |