Faculty of Chemistry, University of Wrocław, Joliot-Curie 14, 50-383 Wrocław, Poland.
Dalton Trans. 2019 Oct 7;48(39):14829-14838. doi: 10.1039/c9dt02916h.
Two organic-inorganic hybrid halobismuthates(iii), (NH2CHNH2)3[Bi2Cl9] (FBC) and (NH2CHNH2)3[Bi2Br9] (FBB), have been prepared with their structures revealed by single-crystal X-ray diffraction at various temperatures. FBC is characterized by one-dimensional (1D) [Bi2Cl9]3-∞ anionic chains built by edge-sharing BiCl6 octahedra, whereas FBB adopts a layer structure (2D) [Bi2Br9]3-∞. Both materials were found to exhibit a rich polymorphism in the solid state. FBC undergoes two reversible phase transitions (PTs) at 218/220 K and at 123/126 K (cooling/heating), respectively, whereas for FBB also two PTs occur close together at 196/199 K and at 190/188 K. Dielectric response around the PT temperatures of FBC and FBB reflects high disorder of dipolar groups over the high temperature phases. The 'order-disorder' mechanism of these PTs is assigned to the dynamics of formamidinium cations. FBB is considered as a ferroic material exhibiting ferroelastic domains below 196 K. The molecular motions of organic cations in a wide temperature range were studied by means of 1H NMR (spin-lattice relaxation time). Presented findings will provide a new method to explore organic-inorganic multifunctional PT materials.
两种有机-无机杂化卤化铋(III)盐，(NH2CHNH2)3[Bi2Cl9] (FBC) 和 (NH2CHNH2)3[Bi2Br9] (FBB)，通过单晶 X 射线衍射在不同温度下揭示了其结构。FBC 的特征是一维（1D）[Bi2Cl9]3-∞阴离子链，由边缘共享的 BiCl6 八面体构建，而 FBB 采用层状结构（2D）[Bi2Br9]3-∞。这两种材料在固态中都表现出丰富的多晶型现象。FBC 在 218/220 K 和 123/126 K（冷却/加热）处经历了两个可逆相变（PT），而 FBB 在 196/199 K 和 190/188 K 处也发生了两个接近的 PT。FBC 和 FBB 的 PT 温度周围的介电响应反映了高温相中二极基团的高度无序。这些 PT 的“有序-无序”机制归因于甲脒阳离子的动力学。FBB 被认为是一种铁电材料，在 196 K 以下表现出铁弹性畴。通过 1H NMR（自旋晶格弛豫时间）研究了有机阳离子在宽温度范围内的分子运动。所提出的发现将为探索有机-无机多功能 PT 材料提供一种新方法。
