Catalysis by polyoxometalates. Part 1.—Supported polyoxoanions of the Keggin structure: spectroscopic study (IR, Raman, UV) of solutions used for impregnation

Solutions of Keggin-structure polyoxometalates have been studied by IR, Raman and UV spectroscopies, with various solvents and counterions. For the tetraalkylammonium compounds, cation–anion aggregates are observed. This model of cation–anion aggregates can be applied to the solutions of the acids in DMF and DMSO. The different behaviour of the acids in water, acetonitrile and acetone can be explained in terms of anion–anion interactions, similar to those existing in the solid state. The results are discussed in connection with the use of polyoxometalate solutions for preparing supported catalysts by impregnation.