Crystal structure of bis[hydroxo(triphenyl)arsonium(V)] dodeca-µ-chloro-hexachloro-octahedro-hexaniobate(2–)

Abstract

The crystal structure of the title compound has been determined by single-crystal photographic X-ray diffraction methods. The structure was solved from photographic data by the heavy-atom method and refined by block-diagonal least-squares to R 0·13 for 2326 reflections. Crystals are monoclinic, space group, P2₁/n a= 15·76(2)b= 22·25(3), c= 8·62(1)Å, β= 91·6(3)°Z= 2. The asymmetric unit is a [Ph₃AsOH]⁺ cation and one half of a centrosymmetric [(Nb₆Cl₁₂)Cl₆]^2– anionic cluster unit. Bond lengths within the cation agree well with previously determined values for similar species (mean C–C 1·39, mean C–As 1·91 Å); As–O is 1·73(2)Å. The proximity of this bond to the special position (½,0,0), (0 ½,½) and the O–O′ distance of 2·80 Å suggests that the cation oxygens are linked by a pair of hydrogen bonds. The point-symmetry of the cluster does not differ significantly from O_h the octahedron of niobium atoms (mean Nb–Nb 3·01₆Å) being surrounded by the usual two sets of axial (6) and edge (12) chlorine atoms, (mean Nb–Cl 2·48 and 2·24 Å). These distances differ significantly from those found in clusters of different oxidation state.