The crystal structure of Nb3O2Cl5, an original Nb3 cluster oxyhalide

The new Nb3O2Cl5 oxychloride was synthesized at 700°C in a sealed silica tube from a stoichiometric mixture of NbCl5, Nb2O5, and Nb. The crystal structure of this new compound was determined by single crystal X-ray diffraction (Pnnm, a = 8.060(2), b = 14.496(3), c = 6.695(2) Å, V = 782.2(4) Å3, Z = 4; dcalc = 4.14 g/cm3, R = 0.036, Rω = 0.047). It consists of [Nb3(μ3-Cli)(μ2-Cli)(μ3-Oi–a)2/2(μ3-Oa–i)2/2(μ2-Cla–a)4/2(μ3-Cla–a–a)3/3] units, in which the Nb3 triangle is face-capped by one chlorine atom and edge-capped by one chlorine and two oxygen atoms. In addition, each of the two oxygens is linked to an adjacent Nb3 cluster, while Cla–a and Cla–a–a bridge two and three Nb3 clusters, respectively. The new Oi–a ligand gives relatively short Nb–Nb intercluster distances (3.50 Å). The linkages between the clusters lead to zigzag chains along two directions of the space, building layers bridged together by chlorine atoms. In this compound, six valence electrons remain for the Nb–Nb bonding states, a good agreement with previous molecular orbital calculations performed on Nb3 cluster compounds.