Our prototype of a porous metal-organic crystal composed of a catenane-based backbone was constructed using a catenane ligand with four carboxylic acids. Green crystals were obtained by heating the ligands and cobalt ions in N,N-dimethylformamide (DMF).

Using single-crystal X-ray diffraction, it was found that the deprotonated carboxyl groups of catenanes are linked by cobalt ions to form a linear chain structure, and these chains are linked vertically and horizontally by the mechanical bond of catenanes. It was also revealed from various X-ray diffraction analysis, this porous crystal can dynamically change its geometry upon guest molecule release, uptake and exchange, and also upon temperature variation even in a low temperature range.

The mechanical properties was examined by nano-indentation. It was found that the material deformed easily when pressed mechanically—and that its Young's modulus (E), an index of the ease with which it deforms, is comparable to that of polypropylene. Surprisingly, the crystal returned to its original shape, without damage, upon removal of the force. Furthermore, when isostatically compressed, the crystal is compressed most in a specific direction. The crystal structure obtained at a high pressure showed the deformable nature of the crystal comes from the slipping motion between the rings of the catenane molecules.