A versatile entry into aqueous niobium chemistry: isolation and structure of the intermediate Nb4(mu2-O)2(mu2-OC2H5)4Cl2(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(mu2-O)2(mu2-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 centro¬symmetric tetrameric Nb(IV) complex, consisting of a pair of edge-sharing bi-octahedral Nb2(mu2-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.