The crystal structure of Nb3O2Cl5, an original Nb-3 cluster oxyhalide

The new Nb3O2Cl5 oxychloride was synthesized at 700 degrees C in a sealed s ilica tube from a stoichiometric mixture of NbCl5, Nb2O5, and Nb. The cryst al structure of this new compound was determined by single crystal X-ray di ffraction (Pnnm, a = 8.060(2), b = 14.496(3), c = 6.695(2) Angstrom, V = 78 2.2(4) Angstrom(3), Z = 4; d(calc) = 4.14 g/cm(3), R = 0.036, R-w = 0.047). It consists of [Nb-3(mu(3)-Cl-i)(mu(2)-Cl-i)(mu(3)-Oi-a)(2/2)(mu(3)-Oa-i)( 2/2)(mu(2)-Cla-a)(4/2)(mu(3)-Cla-a-a)(3/3)] units, in which the Nb-3 triang le 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 adja cent Nb-3 cluster, while Cla-a and Cla-a-a bridge two and three Nb-3 cluste rs, respectively. The new Oi-a ligand gives relatively short Nb-Nb interclu ster distances (3.50 Angstrom). The linkages between the clusters lead to z igzag chains along two directions of the space, building layers bridged tog ether 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 Nb-3 cluster compounds. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.