H 4 [SiMo 12 O 40 ] can take part in redox reactions as well as electrophilic transformations. The reduction of Mo(VI) to Mo(V) in various solvents was followed by ESR spectroscopy. The spectra show significant rhombic splitting, which can be correlated with the dielectric constants of the solvents. Coordination of solvents distorts the symmetry of MoO 6 octahedra. Based on the degree of splitting it is suggested that the strength of coordination decreases in the sequence: acetone>ethanol>1,4-butanediol>acetonitrile>DMSO. The comparison of 95 Mo NMR chemical shift data obtained in various solvents and the results of modelling solvent-solute interactions indicated, however, that dimethyl sulfoxide (DMSO) interacts most strongly with the Mo sites of unreduced acid.
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