SYNTHESIS, STRUCTURE, AND PROPERTIES OF LINB6CL15

Black single crystals of LiNb6Cl15 were obtained from reactions of Nb powder, NbCl5 and LiCl in sealed niobium tubes at 850 degrees C. The h eavy atom structure of LiNb6Cl15 (<Ia(3)over bar d> (no. 230), Z = 16, a = 2055.5(2) pm at 100 K, R(F) = 0.028, R(F-2) = 0.053) is isotypic with the structure of Ta6Cl15. The [Nb6Cl12](2+) clusters in the struc ture are threedimensionally interconnected via three additional Cla-a. These bridge all vertices of niobium clusters, consistent with [(Nb6C l12Cl6/2a-a)-Cl-i](-) (the Nb-Cla-a-Nb angles are 140 degrees). At low temperatures the lithium ions are disordered over one-third of sites (48f), occupying cavities inside of two distorted corner-sharing tetra hedra of chloride. These positions for lithium represent the narrowest sections of infinite channels in the structure built up by chloride. An increased lithium ion mobility is obtained above 170 K by Li-7-NMR measurements.