| 研究実績の概要 |
Polycatenation is one of the commonly observed entanglement patterns in metal-organic frameworks (MOFs, where 0D, 1D or 2D motifs are connected through mechanical bonds to give a framework of a higher dimension. Usually the formation of mechanical bonds within polycatenated MOFs mainly rely on the crystallization process which is sensitive to subtle reaction conditions. As a result, the outcome of the topology is usually difficult to predict, and the synthesis of polycatenated MOFs is quite serendipitous.
Here we report a more controlled method to synthesize polycatenated MOFs by using a ligand that contains a mechanical bond. Mechanically interlocked molecules (MIMs), such as catenanes and rotaxanes have been introduced into MOFs, but the mechanical bond only acts as the pendant of the ligand. In this work, a tetra-functionalized [2]catenane was designed to have two carboxylic acid groups on each macrocycle. When the ligand reacted with suitable metal ions such as Co(II), [2]catenanes are connected by paddlewheel units to produce a 3D framework with the mechanical bond of the catenanes forms a part of the backbone. This catenane-backboned MOF was found to be able to sense subtle environmental change, as revealed by the temperature- and solvent-dependent polymorphism. More importantly, the crystal was found to be a mechanically softest crystal.
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