STUDIES IN HEAVY-METAL MOLYBDATES .2. CRYSTAL-STRUCTURE OF DISODIUM DI-MU-HYDROXO-DIZINC(II) MOLYBDATE
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Sodium -hydroxo--aquo-dizinc(II) molybdate, NaZn2(OH)(H2O)(MoO4)2, was found to form a compound of composition NaZn(OH)MoO4 when allowed to react in a pressure bomb with 4 M sodium molybdate. The crystals are orthorhombic with a = 7.850 (1), b = 9.2922 (8), c = 6.148 (1) , and V = 444.4 3. Systematic absences fixed the space group as Pna21. The density, determined by flotation in a thallous formate-thallous malonate solution, was ~4 g cm-3 compared to a calculated density with Z = 4 of 3.965 g cm-3. A total of 843 intensities above background were collected by counter diffractometry using the -2 scan technique. The structure was solved by a combination of Patterson and Fourier methods. Refinement by block-diagonal least-squares procedures led to a final RF of 0.038 and a weighted residual RwF of 0.036. The zinc atoms are octahedrally coordinated by oxygen atoms which share edges forming infinite chains of octahedra. These chains are linked by molybdate tetrahedra to form zinc molybdate sheets. The sheets are not separated by sodium ions as in NaZn2(OH)(H2O)MoO4 but are interconnected through both molybdate groups and sodium ions. The hydrogen atom was placed on the oxygen which bridges zinc atoms based upon electrostatic bond strength considerations. This made the structure a disodium di--hydroxo-dizinc(II) molybdate. 1977, American Chemical Society. All rights reserved.
