The phase transition, thermal isomerization and formation of a novel crystal structure out of cis-1-thioniabicyclo [4. 4. 0] decane bromide (cis-TBD-Br) and its trans isomer (trans-TBD-Br) were investigated by means of differential thermal analysis, X-ray diffraction and infrared absorption spectrometry. The cis-TBD-Br having a monoclinic C-lattice at room temperature is transformed into an orthorhombic F-lattice at 126°C. With continuous heating up to 180°C, the cis-TBD cations in this lattice are gradually isomerized into the cis and trans equilibrium state. This equilibrated compound forms a novel α-TBD-Br crystal, in which the ratio of the cis-and trans-TBD cations are approximately 3 : 2. The trans-TBD-Br having an orthorhombic C-lattice at room temperature is transformed into an orthorhombic F-lattice at 108°C, and then also isomerized into the α-TBD-Br. At room temperature, the α-TBD-Br can be kept for several days in a desiccator over silica gel. After that it gradually decomposes into its component crystals, cis-and trans-TBD-Br. As the α-TBD-Br lattice contains four formular units, C
9H
11SBr, the space group is restricted to one of Fmmm, Fmm2 and F222. It is concluded that, since the isomeric cis-and trans-TBD cations are distributed statistically around four equivalent positions having a site symmetry (mmm, mm2 or 222) given by the space group, these cations should have statistical orientations.
抄録全体を表示