X-Ray Structural Characterization of the Protonation Sites in the Dihydrogenhexaniobate Anion

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Abstract
Direct evidence for the locations of the hydrogen atoms in the dihydrogenhexaniobate anion has been obtained by a single-crystal X-ray diffraction method. Hexasodium dihydrogenhexaniobate icosahydrate (1), Na6[H2Nb6O19]·20H2O, crystallizes in triclinic form, space group , a = 10.364(2), b = 12.205(2), c = 9.026(2) Å, α = 103.21(2), β = 111.10(2), γ = 109.27(2)°, V = 924.0(5) Å3, Z = 1. The hexaniobate anion in 1 is protonated at two bridging oxygen atoms with the O–H distance of 0.69(6) Å. Due to the protonation and interactions with the Na+ counter-cations, the point symmetry of the hexaniobate anion is reduced to C2h from its possible highest symmetry of Oh.