Structural Investigation of a Flexible MOF [Cu(BF4)2(1,3-bis(4-pyridyl)propane)2] Showing Selective Gate Adsorption with Dynamic Pore-Opening/Pore-Closing Processes

Structural analyses of a flexible 1D MOF [Cu(BF4)(2)(bpp)(2)] (bpp=1,3-bis(4-pyridyl)propane) with/without guest molecules were performed by synchrotron powder X-ray diffraction analysis and single crystal structural analysis. The guest-free MOF is composed of ID chains composed of Cu(II) ions and bpp ligands which are accumulated to form quasi-2D layers, resulting in a quasi-layered compound. The guest-free MOF has no open pore windows; it, however, has latent quasi-hexagonal cavities surrounded by six BF4 anions. This MOF shows molecular selective sorption, which stems from guest-dependent dynamic structural transformation including pore-opening/closing processes. It shows selective alcohol sorption based on the molecular recognition properties; it sorbs C1-C3 alcohols, but not a C4 alcohol (1-butanol). Sorption properties can be enhanced by accumulation of several functionalities. In the case of the flexible MOF, the sorption properties should be synergetically enhanced by several key properties; it has molecular recognition properties and accommodate selected species with pore-opening, and furthermore prevent other species from entering cavities by pore-closing.