Department of Physical Science, Osaka Prefecture University^* RIKEN SPring-8 Center / JASRI / CREST(JST)^** Department of Synthetic Chemistry and Biological Chemistry, Kyoto University^*** Department of Physics, Okayama University^****
○Yoshiki Kubota^* Masaki Takata^** Ryotaro Matsuda^*** Ryo Kitaura^*** Susumu Kitagawa^*** Tatsuo C Kobayashi^****

Metal-organic microporous materials (MOMMs) are the new class of materials with functionalized nano-coordination space and have attracted attention for their application, such as gas storage, gas separation and catalysis. Recently, we reported the highly controlled acetylene accommodation in the nanochannels of MOMM by the in situ synchrotron powder diffraction experiment of gas adsorption and the MEM/Rietveld charge density analysis. While sorption profiles of MOMMs with saturated amounts of guests have been well characterized so far, their intermediate profiles are still unknown. An in-depth understanding of the intermediate state provides us with a feasible design for a porous framework, which changes its structure into one well suited for a desired guest molecules and results in an efficient accommodation system. Therefore, the structural information throughout adsorption phenomena is eagerly required.
Here we report the structure analysis of the intermediate phase in the process of acetylene adsorption in the nanochannels of a MOMM. Crystal lattice was found to expand once in the intermediate phase and contract in the saturated adsorbed phase. Simultaneously the lattice shearing and the rotation of pillar ligand occurred to attain an efficient guest accommodation. These findings will provide us with the guiding principles for a design of gas storage materials for highly reactive gases like acetylene.