Two three-dimensional metal–organic compounds of the formula Pyr₂KM(CN)₆, where M = Co, Fe and Pyr = pyrrolidinium ((CH₂)₄NH₂⁺), have been found to crystallize at room temperature in a monoclinic structure, space group P2₁/c. They are cyano-bridged compounds with an unprecedented type of architecture containing pyrrolidinium cations in the voids. The materials have been investigated by X-ray diffraction, dielectric, and spectroscopic methods as a function of temperature in order to determine their properties and the mechanism of the reversible phase transitions occurring at ca. 345–370 K. The phase transitions in both crystals are first order and are associated with a symmetry increase to a rhombohedral structure (space group R3̅m) as well as a significant disorder of organic cations above T_c. On the basis of Raman scattering and IR spectroscopy it has been assumed that the phase transition in both crystals is triggered by thermally induced pseudorotation of the organic cation and large out-of-plane motions of its atoms followed by a “click-in” of the cyanide bridges. The materials have been proposed as possible switchable dielectrics due to their respective high differences in dielectric permittivities across the phase transition.

中文翻译：

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基于吡咯烷鎓的氰化物：由无序过程触发的异常结构和介电切换性。

发现了两个分子式为Pyr ₂ KM（CN）₆的三维有机金属化合物，其中M = Co，Fe和Pyr =吡咯烷鎓（（CH ₂）₄ NH ₂ ⁺）在室温下结晶。单斜结构，空间群P 2 ₁ / c。它们是具有空前类型的结构的氰基桥接化合物，在空隙中包含吡咯烷鎓阳离子。已经通过X射线衍射，介电和光谱学方法研究了材料作为温度的函数，以确定它们的性质以及在约1℃发生的可逆相变的机理。345-370在两个晶体K的相变是一阶，并且与对称增加一个菱形结构（空间群相关联- [R 3中号）以及有机阳离子上方的显著病症Ť _Ç。根据拉曼散射和红外光谱，已经假设两种晶体的相变是由有机阳离子的热诱导假旋转和其原子的大平面外运动以及随后的“咔嗒”声触发的。氰化物桥。由于材料在相变过程中的介电常数不同，它们被认为是可能的可切换电介质。