Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, Tokyo, Japan.
Research Center for Functional Materials, National Institute for Materials Science, Ibaraki, Japan.
Nature. 2021 Oct;598(7880):298-303. doi: 10.1038/s41586-021-03880-x. Epub 2021 Oct 13.
What particular mechanical properties can be expected for materials composed of interlocked backbones has been a long-standing issue in materials science since the first reports on polycatenane and polyrotaxane in the 1970s. Here we report a three-dimensional porous metal-organic crystal, which is exceptional in that its warps and wefts are connected only by catenation. This porous crystal is composed of a tetragonal lattice and dynamically changes its geometry upon guest molecule release, uptake and exchange, and also upon temperature variation even in a low temperature range. We indented the crystal along its a/b axes and obtained the Young's moduli of 1.77 ± 0.16 GPa in N,N-dimethylformamide and 1.63 ± 0.13 GPa in tetrahydrofuran, which are the lowest among those reported so far for porous metal-organic crystals. To our surprise, hydrostatic compression showed that this elastic porous crystal was the most deformable along its c axis, where 5% contraction occurred without structural deterioration upon compression up to 0.88 GPa. The crystal structure obtained at 0.46 GPa showed that the catenated macrocycles move translationally upon contraction. We anticipate our mechanically interlocked molecule-based design to be a starting point for the development of porous materials with exotic mechanical properties. For example, squeezable porous crystals that may address an essential difficulty in realizing both high abilities of guest uptake and release are on the horizon.
自 20 世纪 70 年代首次报道多轮烷和聚轮烷以来,由交错骨架组成的材料能表现出何种特殊力学性能一直是材料科学领域的一个长期存在的问题。在这里,我们报告了一种三维多孔金属-有机晶体,它的独特之处在于其经纱和纬纱仅通过轮烷键连接。这种多孔晶体由四方晶格组成,在释放、吸收和交换客体分子以及在低温范围内随温度变化时,其几何形状会发生动态变化。我们沿着其 a/b 轴对晶体进行压痕实验,在 N,N-二甲基甲酰胺中得到的杨氏模量为 1.77±0.16GPa,在四氢呋喃中为 1.63±0.13GPa,这是迄今为止报道的多孔金属-有机晶体中最低的。令我们惊讶的是,静水压缩表明,这种弹性多孔晶体在其 c 轴方向上最具可变形性,在压缩至 0.88GPa 时,c 轴方向上发生 5%的收缩而不会导致结构恶化。在 0.46GPa 下获得的晶体结构表明,轮烷大环在收缩时发生平移运动。我们预计我们基于机械互锁分子的设计将成为开发具有奇特力学性能的多孔材料的起点。例如,具有可压缩性的多孔晶体可能会解决实现客体高吸收和释放能力的一个基本难题。