Crystal structure and molecular motion of tetramethylammonium hexaiodotellurate(IV)-iodine (1/1) compound.

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The crystal structure of the title compound was determined by means of X-ray diffraction. The crystal data and the final R value are: [(CH3)4N]2TeI6·I2, tetragonal I41/acd, a=20.356(3) and c=27.571(5) Å, V=11,424(3) Å3, Z=16, R=0.082 for 1562 observed unique reflections. The structure consists of discrete [TeI6]2− anions and Me4N+ cations in an arrangement analogous to the K2PtCl6 structure and of additional I2 molecules bridging adjacent complex anions. The TeI6 octahedron is considerably distorted with Te-I distances of 2.933 (2), 3.017 (2), and 2.857 (2) Å, owing to different interaction with the surrounding I2 molecules. Two of three independent Me4N+ cations are orientationally disordered and distributed over each two positions. A phase transition was found at 234 K from DTA and its molar enthalpy was estimated to be approximately 2.4 kJ mol−1 from DSC. Proton NMR studies offered direct evidences for threefold reorientation of CH3 groups and overall rotation of Me4N+ cations taking place consecutively far below room temperatures. At 234 K the spin-lattice relaxation time T1 changes discontinuously by about one order of magnitude, suggesting the first order of transition. The activation energies of such composite reorientation in the fast regions (ωτc<<1) are 5.4 and 14.2 kJ mol−1 in the high- and low-temperature phases, respectively.
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