Yamashita Satoshi, Nakazawa Yasuhiro, Yamanaka Shusuke, Okumura Mitsutaka, Kojima Tatsuhiro, Yoshinari Nobuto, Konno Takumi
Department of Chemistry, Graduate School of Science, Osaka University, Machinakeyama 1-1, Toyonaka, Osaka, 560-0043, Japan.
Sci Rep. 2018 Feb 8;8(1):2606. doi: 10.1038/s41598-018-20750-1.
In natural ionic solids, cationic and anionic species are alternately arranged to minimize electrostatic energy. Aggregation of identical ionic species is commonly prohibited due to the repulsive, long-range nature of Coulombic interactions. Recently, we synthesized unique ionic solids, [AuCo(dppe)(D-pen)]X·nHO (dppe = 1,2-bis(diphenylphosphino)ethane, D-pen = D-penicillaminate), in which complex cations are self-assembled into a cationic supramolecular octahedron, while monovalent or divalent inorganic anions are aggregated into an anomalous anionic cluster accommodating several water molecules. This quite unusual aggregation manner originates from various molecular-level non-Coulombic interactions such as hydrogen bonds and CH-π interactions; thus, this class of ionic solids is referred to as non-Coulombic ionic solids, abbreviated as NCISs. Herein, we report that the NCISs with a peculiar charge-separated (CS) structure in a cubic lattice show a negative, isotropic electrostriction phenomenon that has never been found in any ionic solids, as well as an anomalously large relaxer-like dielectric jump phenomenon reaching to an application level of ε'/ε ~ 10. The appearance of these phenomena was explained by the cooperative dynamics of inorganic anions and dipolar water molecules in the pliable anionic clusters that are surrounded by a rather robust cationic metallosupramolecular framework with a meso-scopic scale.
在天然离子固体中，阳离子和阴离子物种交替排列以最小化静电能。由于库仑相互作用具有排斥性和长程性，相同离子物种的聚集通常受到抑制。最近，我们合成了独特的离子固体[AuCo(dppe)(D-pen)]X·nH₂O（dppe = 1,2-双（二苯基膦基）乙烷，D-pen = D-青霉胺），其中络合阳离子自组装成阳离子超分子八面体，而一价或二价无机阴离子聚集形成容纳几个水分子的异常阴离子簇。这种非常不寻常的聚集方式源于各种分子水平的非库仑相互作用，如氢键和CH-π相互作用；因此，这类离子固体被称为非库仑离子固体，简称为NCISs。在此，我们报道在立方晶格中具有特殊电荷分离（CS）结构的NCISs表现出一种在任何离子固体中都从未发现过的负的、各向同性的电致伸缩现象，以及一种异常大的类似弛豫体的介电跃变现象，其达到ε'/ε ~ 10的应用水平。这些现象的出现是由无机阴离子和偶极水分子在柔韧的阴离子簇中的协同动力学所解释的，这些阴离子簇被具有介观尺度的相当坚固的阳离子金属超分子框架所包围。
