Hydrothermal investigation of the barium/molybdenum(VI)/selenium(IV) phase space: Single-crystal structures of BaMoO3SeO3 and BaMo2O5(SeO3)(2)

The barium/molybdenum(VI)/selenium(IV)/oxide phase space has been investigated using hydrothermal methods. The syntheses and crystal structures of BaMoO3SeO3 and BaMo2O5(SeO3)(2) are reported. Spectroscopic and thermogravimetric data for these phases are described. BaMoO3SeO3 is a layered compound, built up from ''4-rings'' of vertex-sharing MoO6 and SeO3 groups, linked into infinite, puckered sheets. Ten-coordinate Ba2+ species provide interlayer charge compensation. The distorted MoO6 octahedron in BaMoO3SeO3 shows an unusual three short + three long Mo-O bond-distance distribution. Crystal data: BaMoO3SeO3, M(r) = 408.23, monoclinic, space group P2(1)/c (No. 14), a = 6.242(3) Angstrom, b = 10.192(3) Angstrom, c = 8.373(2) Angstrom, beta = 94.94(3) degrees, V = 530.6(3) Angstrom(3), Z = 4, R(F) = 2.87 %, R(w)(F) = 3.82 % [1653 reflections with I > 3 sigma(I)]. BaMo2O5(SeO3)(2) is a three-dimensional phase with respect to Mo-O-Mo and Mo-O-Se connectivity. Isolated, vertex-sharing pairs of MoO6 octahedra are linked into a continuous network by pyramidal selenium atoms (as SeO32- selenite ions). The MoO6 octahedra in BaMo2O5(SeO3)(2) display a typical two short + two intermediate + two long Mo-O bond-distance distribution. Ten-coordinate barium cations provide charge compensation. Crystal data: BaMo2O5(SeO3)(2), M(r)= 663.13, orthorhombic, space group Cmc2(1) (No. 36), a = 15.883(4) Angstrom, b = 7.887(2) Angstrom, c = 7.780(2) Angstrom, V = 974.5(4) Angstrom(3), Z = 4, R(F) 2.22 %, R(w)(F) = 2.65 % [943 reflections with I > 3 sigma(I)]. (C) 1996 Academic Press,Inc.