WATER-RICH MOLYBDOTELLURATES - PREPARATION AND CRYSTAL-STRUCTURE OF LI6[TEMO6O24].18H2O AND LI6[TEMO6O24].TE(OH)6.18H2O

Li6[TeMo6O24] . 18H2O is triclinic (space group P1BAR, a = 1041.7(1), b = 1058.6(1), c = 1070.8(1)pm, alpha = 61.08(1), beta = 60.44(1), gamma = 73.95(1)-degrees). Single crystal X-ray structure analysis (Z = 1, 295 K, 317 parameters, 3973 reflections, R(g) = 0.0250) revealed an infinite branched chain of edge-sharing Li coordination polyhedra to be the prominent structural feature. One of the four crystallographically independent Li+ is coordinated octahedrally. The coordination polyhedra of the remaining Li+ are distorted trigonal bipyramids. Only three unique oxygen atoms (O(9), O(10), O(12)) of the centrosymmetric [TeMoO24]6- anion are bound to Li+. The further positions in the coordination spheres of the Li+ are occupied by water molecules. Intermolecular hydrogen bonds involve mainly oxygen atoms of the [TeMo6O24]6- anion as nearly equivalent proton acceptors without regard to their different bonding modes to Te and Mo, respectively. Li6[TeMo6O24] . R(OH)6 . 18 H2O crystallizes monoclinically in space group P2(1)/n with Z = 4, a = 994.1(3), b = 2344.8(10), c = 1764.9(4) pm, and beta = 91.36(4)-degrees. Single crystal structure analysis with least squares refinement of 627 parameters (5900 reflections, 295 K) converged to R(g) = 0.0324. There are six unique Li+ cations. The coordination polyhedra of Li(1), Li(2), Li(3), and Li(4) are linked by common edges to yield an eight membered centrosymmetric strand. The coordination polyhedra of the remaining two Li+ sites (Li(5), Li(6)) are connected to a dimeric unit via a common corner. All oxygen atoms of the Te(OH), molecule are involved in the coordination of Li+. However, only three oxygen atoms (O(13), O(18), O(23)) of the [TeMo6O24]6-anion which lacks crystallographic symmetry are involved in the coordination of Li+. The oxygen atoms of the anion act as proton acceptors in hydrogen bonds of predominantly medium strength. Te(OH)6 molecules and [TeMo6O24]6- anions connected by strong hydrogen bonds form an infinite chain.