|Budget Amount *help
¥1,100,000 (Direct Cost : ¥1,100,000)
Fiscal Year 1998 : ¥100,000 (Direct Cost : ¥100,000)
Fiscal Year 1997 : ¥1,000,000 (Direct Cost : ¥1,000,000)
A thiourea inclusion compound having guest molecules of CBr_4 is of interest with respect to the relationship between intermolecular interaction and physical properties. The thermodynamical measurements by Matsuo et al. indicated that the compound undergoes a phase transition estimated to be a order-disorder type at 201.75 K.I took up the compound to elucidate the difference of the crystal structures due to the phase transition, and made a cooling device for a Precession camera refering to Yoshimura's paper, to investigate crystallographycally the low temperature phase by X-ray photograph techniques. A high temperature form of (CH_4N_2S) _3 CBr_4 crystallizes in the trigonal space group R-3c. Channels constructed by hydrogen bondings between thiourea molecules adopt a honey-comb structure and CBr_4 occupies a special 32 position within the channel having a six-fold disorder structure.
It seems reasonable to assume that the honey-comb structure constructed by thiourea molecules is little changed from the configuration in the high temperature form and only the orientation of CBr_4 is changed owing to the phase transition. Slight splittings appeared in the diffraction spots of the low temperature form and disappeared with an increase in temperature above the phase transition point. After various twin lattices were examined to give a satisfactory indexing for splitting spots in the Precession photographs, the compound was found to be a twin sharing an ac face. It belongs to the monoclinic system of unique axis c having gamma^*=62ﾟ, and the possible space groups are P2, Pm and P2/m. However, a 2-fold axis parallel to c axis or a mirror plane perpendicular to one makes it difficult to construct the channels of thiourea, even if any space group is adopted. It is, therefore, considered that the crystal does not belong to the monoclinic but to the triclinic system.