Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, CA, USA.
Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, CA, USA.
Nat Chem. 2021 Mar;13(3):278-283. doi: 10.1038/s41557-020-00618-6. Epub 2021 Feb 15.
Amphidynamic crystals, which possess crystallinity and support dynamic behaviours, are very well suited to the exploration of emergent phenomena that result from the coupling on the dynamic moieties. Here, dipolar rotors have been embedded in a crystalline metal-organic framework. The material consists of Zn(II) nodes and two types of ditopic bicyclo[2.2.2]octane-based linkers-one that coordinates to the Zn clusters through two 1,4-aza moieties, and a difluoro-functionalized derivative (the dipolar rotor) that coordinates through linked 1,4-dicarboxylate groups instead. Upon cooling, these linkers collectively order as a result of correlated dipole-dipole interactions. Variable-temperature, frequency-dependent dielectric measurements revealed a transition temperature T = 100 K, when a rapidly rotating, dipole-disordered, paraelectric phase transformed into an ordered, antiferroelectric one in which the dipole moments of the rotating linkers largely cancelled each other. Monte Carlo simulations on a two-dimensional rotary lattice showed a ground state with an Ising symmetry and the effects of dipole-lattice and dipole-dipole interactions.
具有结晶性和支持动态行为的双稳态晶体非常适合探索由于动态部分的耦合而产生的新兴现象。在这里，偶极子转子被嵌入晶体金属有机骨架中。该材料由 Zn(II) 节点和两种类型的双位双环[2.2.2]辛烷基连接体组成-一种通过两个 1,4-氮杂部分与 Zn 簇配位，另一种是二氟功能化衍生物（偶极子转子），通过连接的 1,4-二羧酸酯基团配位。冷却时，这些连接体由于相关的偶极-偶极相互作用而集体有序。变温、频率相关介电测量显示出转变温度 T=100 K，当快速旋转的、偶极无序的顺电相转变为有序的反铁电相时，旋转连接体的偶极矩相互抵消。二维旋转晶格上的蒙特卡罗模拟显示出具有伊辛对称性的基态以及偶极-晶格和偶极-偶极相互作用的影响。
