Structural Transformation and Spatial Defect Formation of a Co(II) MOF Triggered by Varied Metal-Center Coordination Configuration.

In spite of the attractive potential application of the dynamic behavior and defect of metal–organic framework (MOF), the achievement of these features is a challenging goal in the MOF research field. Herein, we report a Co­(II) MOF, namely, [Co3(L)2­(4-PTZ)2(H2O)2]n·solvent (H2L = 5-(isonicotinamido)­isophthalic acid, 4-PTZ = 5-(4-pyridyl)-1H-tetrazole), that features dynamic structural transformation behaviors. By varying the coordination configuration of metal center through the removal of coordinated water molecules, the porous compound could undergo structural transformation to give a new crystalline phase with larger pore dimension. Moreover, the new phase features a mesoporous structure originating from the spatial defect that formed with the transformation process, which indicates that the modulation of dynamic behavior of the MOF could be a potential method for the engineering of a spatial defect. In addition, the gas sorption investigation results reveal that the new phase has enhanced selectivity for CO2/N2, CO2/CH4, and C2H2/C2H4 systems compared with that of the pristine phase, suggesting the potential of spatial defect engineering for the tuning of MOF gas sorption properties.