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 inve stigated using hydrothermal methods. The syntheses and crystal structu res 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 a nd SeO3 groups, linked into infinite, puckered sheets. Ten-coordinate Ba2+ species provide interlayer charge compensation. The distorted MoO 6 octahedron in BaMoO3SeO3 shows an unusual three short + three long M o-O bond-distance distribution. Crystal data: BaMoO3SeO3, M(r) = 408.2 3, 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-dimensi onal phase with respect to Mo-O-Mo and Mo-O-Se connectivity. Isolated, vertex-sharing pairs of MoO6 octahedra are linked into a continuous n etwork by pyramidal selenium atoms (as SeO32- selenite ions). The MoO6 octahedra in BaMo2O5(SeO3)(2) display a typical two short + two inter mediate + two long Mo-O bond-distance distribution. Ten-coordinate bar ium cations provide charge compensation. Crystal data: BaMo2O5(SeO3)(2 ), M(r)= 663.13, orthorhombic, space group Cmc2(1) (No. 36), a = 15.88 3(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.