Incommensurate guest adsorption in bellows-shaped one-dimensional channels of porous coordination polymers

Adsorption isotherms of N₂, O₂, CO₂, and Xe on a flexible microporous coordination polymer, CPL-2 [Cu₂(pzdc)₂(bpy)]·(pzdc = pyrazine-2,3-dicarboxylate; bpy = 4,4′-bipyridine), possessing bellows-shaped one-dimensional channels were measured. A nonintegral number of each of the N₂, O₂, CO₂, and Xe molecules can be accommodated in each unit pore, which indicates that all guest molecules are accommodated in the so-called "incommensurate fashion". In situ synchrotron X-ray powder diffraction patterns of CPL-2 with guest molecules were recorded. The unit cells were determined from each pattern. It was found that the host CPL-2 exhibits different crystal transformation with the accommodation of each guest molecule. This indicates that, even in the case of incommensurate adsorption, the flexible framework of a microporous coordination polymer can transform each pore to suit different guest molecules.