HEXAAQUA DIPOSITIVE IONS OF THE 1ST TRANSITION SERIES - NEW AND ACCURATE STRUCTURES - EXPECTED AND UNEXPECTED TRENDS

An accurate, X-ray crystallographic redetermination of the structures of both the ammonium Tutton salts and the hexafluorosilicates of the divalent hexaaqua species that are formed by the elements of the first transition series, namely, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, is presented here. For the Tutton salts, the metal-to-water bond distances show minima at vanadium and nickel as expected from ligand field theory considerations. For the second series of compounds, vanadium and chromium deviate unexpectedly from the pattern. A comparison of the variation of the metal-to-water distances in other hexaaqua compounds is also given and the general trends are discussed. Special attention is given to the suppression of the Jahn-Teller effect in the hexaaqua hexafluorosilicate compounds of Cr(II) and Cu(II).