MOTIONS OF TETRAMETHYLAMMONIUM CATIONS AND PHASE-TRANSITIONS IN SOLID [(CH3)4N]2CDCL4, [(CH3)4N]2CDBR4, [(CH3)4N]2CDI4 AS STUDIED BY H-1-NMR, POWDER X-RAY-DIFFRACTION, AND DIFFERENTIAL THERMAL-ANALYSIS MEASUREMENTS

The temperature dependences of 1H spin-lattice relaxation times were determined at 20 MHz for [(CH3)4N]2CdCl4, [(CH3)4N]2CdBr4, and [(CH3)4N]2Cdl4. For the last two complexes, the frequency dependence of the relaxation time was observed above room temperature. lH NMR second moments were observed for the bromide complex. At room temperature, the first two complexes were found to be isomorphous with the iodide complex which forms orthorhombic crystals. Differential thermal analysis experiments revealed that these complexes undergo four, one, and one solid-solid phase transitions in the above order between ca. 80 and 430 K. Two 1H T1 minima were clearly observed at lower temperatures for the chloride and bromide complexes, whereas at least three lH T1 minima partly overlapped with each other were detected at lower temperatures for the iodide complex. For the former two complexes, the 1H T1 data were well analyzed by the general method already reported. For the bromide and iodide complexes, JH T1 curves observed showed a maximum above room temperature. Motions of the cation activated in these complexes are discussed in relation to the crystal field experienced by the cation. © 1986 The Chemical Society of Japan.