咪唑-氰基合铁(Ⅲ)氢键型超分子晶体的合成、相变及介电性质

通过溶剂蒸发法,咪唑、18-冠醚-6和铁氰酸在甲醇溶液内反应,获得了氰基合铁配合物氢键型笼状超分子晶体材料(C3H5N2)3Fe(CN)6]·2(18-crown-6)·2H2O(1)。通过变温X射线单晶衍射、红外光谱、元素分析、热重分析(TG)、差示扫描量热法(DSC)和变温-介电常数测试等对该晶体进行了结构、热能及电性能分析。该晶体的空间群为P21/c,属于单斜晶系,结构显示氰基合铁阳离子、水分子和咪唑阳离子在空间内通过氢键的相互作用形成以铁原子为顶点的三维笼状结构。温度变化触发笼状结构突变,同时引起Fe(CN)6]3-框架内超分子发生动态摆动,从而引起晶体结构发生相变,该结构相变温度区间伴随介电物理特性阶梯状变化,从220到280 K,介电常数由38变为43,且可逆。温度在270 K之后的介电突然跃升是水汽影响导致。

Synthesis,Phase Transition and Dielectric Properties of Ferrate Cyanogen(Ⅲ) Hydrogen-Bonding Supramolecular Crystal

Synthesis of novel ferric cyanide hydrogen-bonding cage-like supramolecular crystal material (C₃H₅N₂)₃Fe(CN)₆]·2(18-crown-6)·2H₂O (1) by solvent evaporation in methanol solution with imidazole, 18-crown-6 and ferric cyanide. The structure, thermal energy and electrical properties of the crystal were characterized by variable temperature X-ray diffraction single crystal diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and dielectric constant test. The space group of the crystal is P2₁/c, which belongs to the monoclinic system at low temperatures. The crystal structure shows that the cyano-iron complex, the water molecule and the imidazolium cation form a three-dimensional cage structure with iron atoms as the apex in the form of hydrogen bonds. This resulted in phase transition at around 250 K and stepped reversible dielectric anomalies in a range of 220~260 K. Temperature variation triggers the cage structure abrupt change, and at the same time causes dynamic oscillation of supramolecules within the framework ofFe(CN)₆]^3-, thus induces the phase transition of crystal structure. The phase transition temperature interval of the crystal structure was accompanied with step-like change in dielectric physical properties. The dielectric constant was reversible and changed from 38 to 43 with temperature increasing from 220 to 280 K. Above 270 K, the sudden jump in dielectric is caused by water vapor.