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The Crystal Structures of Methylammonium Hexachlorostannate(IV) in the High- and Low-temperature Phases Studied by X-Rays

1979; Oxford University Press; Volume: 52; Issue: 2 Linguagem: Inglês

10.1246/bcsj.52.324

1348-0634

Katsuki Kitahama, Hideko Kiriyama, Yoshihisa Baba,

Advanced NMR Techniques and Applications

Abstract The title compound crystallizes in the trigonal space group R\bar3m with a=7.171, c=21.952 Å, and Z=3 at 298 K. The crystal structures at 298 and 120 K, as well as the lattice parameters in the temperature range 113–298 K, have been determined by X-rays, in order to elucidate the mechanism of the phase transition occurring at Tt=156 K. The structure of the high-temperature phase is essentially the same as that determined by Wyckoff, except for the discrimination between C and N atoms. No change in the space group nor in the basic structure was detected over the temperature range studied, in spite of a strong suggestion from previous 35Cl-NQR measurements. A small but significant anomaly associated with the transition is recognized in the c axis, which retains almost the same length near and below Tt. As a result, the lattice shrinkage below Tt becomes increasingly anisotropic as the temperature is lowered, whereas the thermal expansion above it is relatively isotropic.