SYNTHESIS OF TERNARY POTASSIUM, MAGNESIUM, AND ZIRCONIUM MOLYBDATES -THE CRYSTAL-STRUCTURE OF K-5(MG0.5ZR1.5)CENTER-DOT(MOO4)(6)

Three (5:1:3, 1:1:1, and 2:1:6) ternary phases were discovered in the K2MoO4-AMo0(4)-Zr(MoO4)(2) system, where A is Mg or Mn. For A = Mg, we have synthesized 5:1:3 single crystals and determined their crystal s tructure from X-ray diffraction data (a CAD-4 automatic diffractometer , MoKalpha, radiation, 1166 F(hkl), and R = 0.026). The compound cryst allizes in the trigonal system with space group R3c, a = 10.576(1), c = 37.511(3) Angstrom, Z = 6, d(calc) = 3.576, and d(msd) = 3.54 g/cm(3 ). The structure is a three-dimensional composite framework of alterna ting Mo tetrahedra and (Mg, Zr) octahedra, which are linked via the co mmon O vertices. Potassium atoms of three kinds are located in large f ramework cavities. Their polyhedra (ten-vertex polyhedra and a cubeoct ahedron) are linked together by common faces and edges to form infinit e zigzag columns of a large section. When solving the structure, we re fined the composition of the crystals and the distribution of Mg2+ and Zr4+ cations in the M(1) and M(2) positions resulting in the formula above.