NIH3IO6-CENTER-DOT-6H(2)O - CRYSTAL-STRUC TURES AND VIBRATIONAL-SPECTRA

The crystal structure of NiH3IO6 . 6 H2O has been determined by X-ray single-crystal diffraction (Pc, Z = 2, a = 516.74(9), b = 981.5(2), c = 1052.5(2)pm, beta = 116.496(8)degrees) on the basis of 4169 unique r eflections (R = 1.96%). The structure is built up of distorted Ni(H2O) (6)(2+) and H3IO62- octahedra linked by hydrogen bonding. IR and Raman spectra of both the title compound and isostructural MgH3IO6 . 6H(2)O as well as of deuterated specimens are given. There are up to 14 diff erent OH(OD) modes in the spectra of isotopically dilute samples due t o the 15 different hydrogen positions of the structure. The internal m odes of the meridional H3IO62- ions (pseudo C-2v symmetry) are discuss ed with respect to that double T-shaped entity, which gives rise to on ly two instead of 3 I-O, I-O(H), and OH stretches in the IR and Raman spectra, i.e. the same as for facial (C-3v) structured ions.