2-DIMENSIONAL NETWORKS IN THE STRUCTURE OF LI-2[NB6CL16]

Li-2[Nb6Cl16] has been synthesized from the reaction of Nb powder, NbC l5 and LiCl in sealed silica tubes at 700 degrees C. The structure, as determined by single-crystal X-lay diffraction, is orthorhombic, spac e group Cmca (no. 64) with Z=4 and has lattice parameters a=1274.7(1)p m, b = 1318.5(1) pm, c = 1341.1(2) pm. The refinement of all atomic po sitions yielded R1 = 0.031 (based on F values) and wR2 = 0.081 (based on F-2 values). The structure contains layers formed by [Nb6Cl12i](2+) with outer Cla-a ligands that bridge four vertices of each octahedral niobium cluster into sheets, plus two terminal Cl-a ligands of each c luster, to be described as [(Nb6Cl12Cl4/2a-aCl2a)-Cl-i](2-). The same connectivity pattern is pre sent for binary Mo6X12 halides, containing eight inner halide ligands (Mo6Cl8i). Non-linear Nb-Cla-a-Nb bridges (159 degrees) correspond with intra-layer rotations of [Nb6Cl16](2-) u nits and thereby accommodate two Li+ in distorted trigonal-bipyramidal voids.