STUDIES IN HEAVY-METAL MOLYBDATES .1. CRYSTAL-STRUCTURE OF A BASIC ZINC MOLYBDATE, NAZN2OH(H2O)(MOO4)21A
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The reaction between Zn(II) solutions and sodium molybdate yields a basic sodium zinc molybdate. The crystals, grown hydrothermally, are monoclinic with a = 9.436 (2) , b = 6.338 (1) , c = 7.679 (1) , = 115.8 (1). Based upon an empirical formula Na0.5H0.5Zn(OH)MoO4 and Z = 4, the calculated density is 4.089 g cm-3. This compares to an observed value, determined by flotation of a single crystal in a thallous formate-thallous malonate solution, of 3.9 g cm-3. The systematic absences indicated a C-centered space group which was confirmed as the centrosymmetric one C2/m by the refinement procedure. Intensity data were collected by counter diffractometer methods (-2 scan) and the structure was solved by Patterson and Fourier methods. Refinement of 789 reflections by block-diagonal methods led to a final Rf = 0.043 and Rwf = 0.041. Zinc atoms lie on inversion centers in the xy plane and are linked to each other through double oxygen bridges. The zinc atoms are octahedrally coordinated by oxygens. The octahedra share edges thus forming chains of zinc-oxygen octahedra parallel to the b axis. The chains are connected to each other through tetrahedral molybdate groups forming zinc-molybdate layers parallel to the xy plane. The layers are linked together by sodium ions lying halfway between them. Only one of the two unique hydrogens could be located with certainty. Placement of the other hydrogen atom was made using Baur's electrostatic bond strength criteria. This placement results in the formula NaZn2(OH)(H2O)(MoO4)2. 1976, American Chemical Society. All rights reserved.
