SYNTHESIS AND CRYSTAL-STRUCTURE OF M[NB6CL15] (M=IN, TL) - NEW TERNARY NIOBIUM HALIDES WITH BRIDGED [NB6CL18](4-) CLUSTERS

New ternary niobium chlorides corresponding to the formula M[Nb6Cl15] (M = In, Tl) were synthesized from solid state reactions of NbCl5, nio bium metal, and MCl3 at 720 degrees C. The crystal structure of In[Nb6 Cl15] was determined from single crystal X-ray diffraction studies. Th e structure was refined in the orthorhombic symmetry (space group Pmma , Z=4) with a=1786.6(1)pm, b=1345.52(8)pm, c = 929.34(8) pm, R-F = 0.0 28 and R-W = 0.037, GooF = 1.06 for ail 1552 unique reflections. The l attice parameters of the isotypic Tl[Nb6Cl15] compound were refined fr om X-ray powder diffraction data: a = 1785.9(2)pm, b = 1347.2(2) pm, c = 930.2(1) pm. The structure of In[Nb6Cl15] is made up of [Nb6Cl18](4 -) clusters linked to each other through terminal chloride ligands to form two sets of chains perpendicular to each other. The chains are li nked through other terminal ligands to yield a three-dimensional netwo rk. The In+ or Tl+ ions are located in a ten coordination site (distor ted bicapped cubic geometry) made up of eight inner and two outer chlo ride ligands.