Phase transitions of organic crystals caused by conformational changes of alkyl chains : observation of intermediate stages with a temperature-resolved single crystal diffraction method

由于晶体的损伤和单晶结构分析在不同温度下的强度测量的困难，对相变过程中的详细结构变化的研究很少。最近，通过开发具有二维探测器的衍射仪，温度分辨结构分析成为可能。具有长链烷基衍生物(CnH_2n_1，n=12，13)的晶体显示为一级反应。在n=13的情况下，在转变过程中保持了单晶态。在264~252K，295,280,273,244和100K的相变过程中，每隔2K进行一次结构分析。酰基脲衍生物iso-C_5H_&lt；11&gt；-CO-NH-CO-NH-C_2H_5的晶体在367K(熔点=378K)发生相变，并在相变过程中保持单晶态。晶体ClCH_2-CO-NH-CO-NH-NH-C_5H_(11)和…的结构分析在98,298,328K和348~374K每2K范围内进行由于晶体结构的破坏，更多地采用粉末衍射法。在这些晶体中，揭示了热膨胀引起的烷基构象变化引起相变的中间阶段和机理。含1，8-二甲氧基菲和二硫代辛基酚配体的五配位硼化合物在高温相Pnma和低温相P2_12_12_1存在二级相变。在相变过程中每2K进行一次随温度变化的结构分析。在热膨胀后，邻苯二酚部分甚至从120K开始振动，在203K变得无序，在每个温度下，用相邻分子对的简单力场势计算了分子间的能量。X-射线晶体结构分析2温度分辨X-射线结构分析(3)相变4)有机晶体(5)粉末衍射法(6-酰基脲-7-吖啶-N-氧基衍生物)(8)五配位硼化合物

Very few studies have been done on the detailed structural changes during transitions, because of the crystal damage and difficulties of intensity measurements for single crystal structure analyses at various temperatures. Recently, temperature-resolved structure analyses became possible through the development of diffractometers with two-dimensional detectors. Crystals of acridin-N-oxyl derivatives with a long alkyl chain (CnH2n+1, n=12, 13) showed that the first order. In the case of the n=13, the single crystalline states were kept during the transition. Structure analyses were carried out every 2 K during the transition from 264 to 252 K and at 295, 280, 273, 244 and 100 K. Crystals of a acylurea derivative, iso-C_5H_<11>-CO-NH-CO-NH-C_2H_5 showed a phase transition at 367K (mp=378 K) and also kept single-crystalline-state during the transition. Structure analyses were performed at 98, 298, 328 K and in the range of 348 ~ 374 K every 2 K. For Crystals ClCH_2-CO-NH-CO-NH-C_5H_<11>, … More powder diffraction method was performed because of crystalline damage. In these crystals, intermediate stages and mechanism of phase transitions caused by the conformational changes of alkyl groups induced by the thermal expansion was revealed. A pentacoordinated boron compound bearing 1, 8-dimethoxyanthracene and dithiocatecholato ligands showed the second-order phase transition, Pnma at high temperature phase and P2_12_12_1 at low temperature phase. Temperature-dependent structure analyses were performed every 2 K during phase transition. Following the thermal expansion, the catecholate moieties begin to librate even from 120 K and become disordered at 203 K. Intermolecular energies were calculated using simple force field potentials for the neighboring molecular pairs at each temperature. The energy barrier between ordered and disordered structures at the transition point was estimated about 1 kJ/molX-ray crystal structure analysis 2 temperature-resolved X-ray structure analysis (3) phase transition 4) organic crystals (5) powder diffraction method (6 acylurea 7 acridin-N-oxyl derivatives (8) pentacoordinated boron compound Less