Zhao Yin-Hua, Liu Shu, Wang Bing-Wu, Wang Zhe-Ming, Gao Song
Beijing National Laboratory for Molecular Sciences, Beijing Key Laboratory of Magnetoelectric Materials and Devices, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China.
Chemistry. 2019 Jul 11;25(39):9303-9314. doi: 10.1002/chem.201901655. Epub 2019 Jun 21.
Three new iso-structural ammonium metal formates of [dmpnH ][M (HCOO) ], in which dmpnH =N,N'-dimethyl-1,3-propylenediammoium and M=divalent Co, Zn and Mg ions, are reported. They possess niccolite metal formate frameworks with long-shaped cavities for the accommodation of dmpnH cations. The three materials display reversible phase transitions of similar mechanism from ordered, antipolar or antiferroelectric, low-temperature phases in space group C2/c, to disordered, paraelectric, high-temperature phases in space group P 1c, with quite high critical temperatures of 366, 370, and 334 K for Co, Zn, and Mg members, respectively. On warming, the dmpnH cation experiences an ordered state with gradual increase of the local vibration motions of the central CH and terminal CH groups, a partially disordered state with gradually enhanced flipping motion between the major and minor orientations, and finally a twisting or rotating motion after the phase transition, accompanied by prominent anisotropic thermal expansions and dielectric anomalies/relaxations. The phase transition characters and relevant properties also exhibit a subtle metal-dependence. The Co member shows spin-canted antiferromagnetism below the Néel temperature of 16.1 K, with unusual large spontaneous magnetization and coercive field.
报道了三种新的同构铵金属甲酸盐[dmpnH][M(HCOO)]，其中dmpnH = N,N'-二甲基-1,3-丙二铵，M = 二价钴、锌和镁离子。它们具有镍黄铁矿金属甲酸盐骨架，带有长形空腔以容纳dmpnH阳离子。这三种材料表现出类似机制的可逆相变，从空间群C2/c中的有序、反极性或反铁电低温相，转变为空间群P 1c中的无序、顺电高温相，钴、锌和镁成员的临界温度分别相当高，为366、370和334 K。升温时，dmpnH阳离子经历有序状态，中心CH和末端CH基团的局部振动运动逐渐增加，部分无序状态，主要和次要取向之间的翻转运动逐渐增强，最后在相变后发生扭曲或旋转运动，伴随着明显的各向异性热膨胀和介电异常/弛豫。相变特征和相关性质也表现出微妙的金属依赖性。钴成员在16.1 K的奈尔温度以下表现出自旋倾斜反铁磁性，具有异常大的自发磁化强度和矫顽场。
