Reversible Transformation of ZnII Coordination Geometry in a Single Crystal of Porous Metal-Organic Framework [Zn3(ntb)2(EtOH)2]⋅4 EtOH

A 3D porous metal‐organic framework [Zn3(ntb)2(EtOH)2]n⋅4nEtOH (1) that generates 1D channels of honeycomb aperture has been prepared by the solvothermal reaction of Zn(NO3)2⋅6 H2O and 4,4′,4′′‐nitrilotrisbenzoic acid (H3NTB) in EtOH at 110 °C. Framework 1 exhibits reversible single‐crystal‐to‐single‐crystal transformations upon removal and rebinding of the coordinating EtOH as well as the EtOH guest molecules, which give rise to desolvated crystal [Zn3(ntb)2]n (1′) and resolvated crystal [Zn3(ntb)2(EtOH)2]n⋅4nEtOH (1′′). The X‐ray structures indicate that 3D host framework is retained during the transformations from 1 to 1′ and from 1′ to 1′′, but the coordination geometry of ZnII ions changes from/to trigonal bipyramid to/from tetrahedron, concomitant with the rotational rearrangement of a carboxylate plane of the NTB3− relative to its associated phenyl ring. To retain the single crystal integrity, extensive cooperative motions must exist between the molecular components throughout the crystal. Framework 1′ exhibits permanent porosity, thermal stability up to 400 °C, and blue luminescence, and high storage capabilities for N2, H2, CO2, and CH4. Reversible coordination geometry in porous metal–organic framework (MOF) crystals: Coordination geometry of ZnII ions in the MOF changes reversibly from/to trigonal bipyramid to/from tetrahedron upon removal and rebinding of the coordinating EtOH molecules in the single‐crystal‐to‐single‐crystal manner (see figure). Even after the removal of the coordinating EtOH molecules as well as the EtOH guest molecules, the MOF exhibits remarkable gas‐adsorption capabilities for N2, H2, CO2, and CH4.