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New mixed-valence chromium structure type: NH4Cr(CrO4)2 |
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| Authors: | Barbara M Casari Erica Wingstrand |
| Institution: | a Department of Chemistry, Inorganic Chemistry, Göteborg University, SE-421 96 Göteborg, Sweden b Department of Chemistry, Organic Chemistry, Royal Institute of Technology, SE 100 44 Stockholm, Sweden c Department of Chemical and Biological Engineering, Division of Material and Surface Chemistry, Subdivision of Inorganic Environmental Chemistry, Chalmers University of Technology, SE-421 96 Göteborg, Sweden |
| Abstract: | Synthesis and crystal structure of a new structure type of mixed Cr(III)/Cr(VI) chromates is reported. NH4Cr(CrO4)2 was prepared from CrO3 in the presence of (NH4)2Ce(NO3)6. Since this is the first preparation of mixed valence ternary chromium oxides from aqueous solution, a reaction pathway for this synthesis is suggested. The crystal structure of NH4Cr(CrO4)2 has been determined from three-dimensional X-ray data collected at low temperature, 173 K. The structure belongs to the orthorhombic space group Pnma, with a=14.5206(10), b=5.4826(4),  and Z=4. The title compound consists of corner-sharing chromium(III) octahedra and chromium(VI) tetrahedra forming a three-dimensional network with the composition Cr(CrO4)2]nn-, containing channels in which zigzag rows of ammonium ions balance the net charge. |
| Keywords: | NH4Cr3O8 Mixed-valence ternary oxide Mixed-valence chromate Cr(VI)/Ce(III) redox reaction X-ray diffraction |
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