A versatile entry into aqueous niobium chemistry: isolation and structure of the intermediate Nb4(μ2-O)2(μ2-OC2H5)4Cl4(OC2H5)4(HOC2H5)4

The reduction of ethanolic solutions of niobium pentachloride with zinc, followed by treatment with aqueous acids serves as a versatile entry into the aqueous solution chemistry of niobium. From the zinc-reduced solution, the major intermediate, Nb4(μ2-O)2(μ2-OC2H5)4Cl4(OC2H5)4(HOC2H5)4, was isolated and the crystal structure determined by X-ray crystallography. The complex crystallizes in the orthorhombic space group Pccn, with Z=4, a=21.0105(9), b=11.0387(5), c=19.1389(8), V=4438.9(3) Å3, Mr=1090.19,R1=0.0327 and wR2=0.0876. The structure revealed a centrosymmetric tetrameric Nb(IV) complex, consisting of a pair of edge-sharing bi-octahedral Nb2(μ2-OC2H5)4Cl2(OC2H5)2(HOC2H5)2 units that are joined by two axial oxo ligands. The Nb–Nb distance of 2.7458(3) Å is consistent with a single metal–metal bond.