The crystal structure of PbLu3Nb6Cl15O6, a new oxychloride based on discrete Nb6Cl12O6 units

A new Nb-6 oxychloride, PbLu3Nb6Cl15O6, has been synthesized from stoichiometric amounts of PbO, Lu2O3, Nb2O5, NbCl5 and Nb, heated at 680 degreesC. The crystal structure has been determined by single crystal X-ray diffraction (cubic, Pn (3) over bar;, a = 13.8327(4)Angstrom, V = 2646.8(1)Angstrom (3), Z = 4). The structure consists of a f.c.c. stacking of discrete edge-capped (Nb6Cl6O6Cl6a)-O-i-Cl-i units in which six oxygen and six chlorine atoms are ordered on the twelve inner positions, while the six apical ones are occupied by six chlorines. Additional chlorines, which do not belong to the former units, are bonded to the lutetium atoms to form Lu2Cl2 entities that occupy 3/4 of the tetrahedral cavities of the stacking units, while the lead ions are randomly distributed in the 1/4 remaining tetrahedral and in the octahedral cavities. The Nb6Cl12O6 units are connected to each other by both the Lu2Cl2 entities and the lead ions to form a three-dimensional framework. This compound exhibits 14 valence electrons per cluster.