Crystal Structure of an Ammonium Nickel Molybdate Prepared by Chemical Precipitation |
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Authors: | Levin Doron Soled Stuart L. Ying Jackie Y. |
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Affiliation: | Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and Exxon Research and Engineering Company, Annandale, New Jersey 08801. |
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Abstract: | A layered ammonium nickel molybdate was prepared by precipitation from a solution of nickel nitrate and ammonium heptamolybdate. The compound obtained, (NH(4))HNi(2)(OH)(2)(MoO(4))(2), is trigonal with hexagonal unit cell parameters a = 6.0147(4) ?, c = 21.8812(13) ?, and Z = 3. A powder X-ray diffraction pattern was obtained using synchrotron radiation. The structure was generated from three-dimensional Patterson and difference Fourier density maps and refined in the space group R&thremacr;m by the Rietveld method. The structure consists of molybdate tetrahedra and nickel octahedra forming layers perpendicular to the c axis. There are three layers per unit cell, with ammonium ions incorporated between the layers. The structure is a member of a solid solution series of (NH(4))H(2)(x)()Ni(3)(-)(x)()O(OH)(MoO(4))(2), where 0 = x = (3)/(2). The nonstoichiometry arises from variable occupancy of the nickel position and allows for the formation of these compounds having Ni/Mo ratios varying from 0.75 to 1.5. |
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