X-RAY STRUCTURAL CHARACTERIZATION OF THE PROTONATION SITES IN THE DIHYDROGENHEXANIOBATE ANION

Direct evidence for the locations of the hydrogen atoms in the dihydro genhexaniobate anion has been obtained by a single-crystal X-ray diffr action method. Hexasodium dihydrogenhexaniobate icosahydrate (1), Na-6 [H2Nb6O19].20H(2)O, crystallizes in triclinic form, space group P (1) over bar, a=10.364(2), b=12.205(2), c=9.026(2) Angstrom, alpha=103.21( 2), beta=111.10(2), gamma=109.27(2)degrees, V=924.0(5) Angstrom(3), Z= 1. The hexaniobate anion in 1 is protonated at two bridging oxygen ato ms with the O-H distance of 0.69(6) Angstrom. Due to the protonation a nd interactions with the Na+ counter-cations, the point symmetry of th e hexaniobate anion is reduced to C-2h from its possible highest symme try of O-h.