A New Niobium Cluster Oxychloride Built from Interconnected Nb6Cl12O6 Units: Na0.21Nb6Cl10.5O3

The new Na0.21Nb6Cl10.5O3 oxychloride was synthesized by a solid state route, from NaCl, Nb2O5, NbCl5, and Nb, heated at 680°C for 2 weeks. The structure was determined by single-crystal X-ray diffraction. It crystallizes in the trigonal system (R c space group, a=11.5048(1) ?, c=44.9446(7) ?, V=5151.88(10) ?3, Z=12). The structure is built from [(Nb6Cli9Oi3) Oa3Cla3] units, which share their inner and apical oxygens forming pseudolayers with short Nb–Nb intercluster distances (3.399 ?). Along the c axis, these layers are interconnected by apical–apical chlorines. The sodium atoms are randomly distributed in the voids arranged between two adjacent layers, in a deformed chlorine prismatic coordination. The developed formula Na0.21 [(Nb6Cli9Oi–a3/2)Oa–i3/2Cla–a3/2] leads to a number of valence electrons per cluster close to 14. This oxychloride will be compared to CsNb6Cl12O2 which we have previously isolated and which was the first example of a Nb6 oxyhalide involving Oi–a, Oa–i interunit connections.