Crystal structure and thermal analysis of the tetramethylammonium dichromate and trichromate |
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| Institution: | 1. State Key Laboratory of Structure Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China;2. University of the Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | The structures of the tetramethylammonium dichromate, (CH3)4N]2Cr2O7 and trichromate, (CH3)4N]2Cr3O10, were determined from single-crystal X-ray diffraction data. These compounds crystallize in the orthorhombic system (space group Pnma, with Z=4 and a=17.192(1) Å, b=8.55(1) Å, c=10.637(1) Å), for the dichromate and in the monoclinic system (space group P21/n, with Z=4 and a=11.366(2) Å, b=8.493(2) Å, c=20.187(4) Å, β=103.98(3)° for the trichromate. The structures consist of discrete dichromate anions (Cr2O7)2– or trichromate anions (Cr3O10)2–, respectively, stabilized by quaternary ammonium (CH3)4N]+. Phase transitions in (CH3)4N]2Cr2O7 have been evidenced by differential scanning calorimetry as well as a new allotropic variety of (CH3)4N]2Cr2O7 which was characterized by X-ray powder diffraction. It crystallizes in an orthorhombic system with the unit cell parameters a=24.49(1) Å, b=8.85(1) Å, c=8.705(8) Å. |
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