Octahedral to Tetrahedral Conversion upon a Ligand-Substitution-Induced Single-Crystal to Single-Crystal Transformation in a Rectangular Zn(II) Metal–Organic Framework and Its Photocatalysis

A new cationic rectangular zinc(II) metal–organic framework (MOF) containing flexible chainlike bridging glutarate (glu) and rigid rodlike 4,4′-bipyridine (4,4′-bipy) ligands with an encapsulated perchlorate counteranion, {[Zn3(4,4′-bipy)4(glu)2](ClO4)2}n (1; P1̅), was studied. Complex 1 has been successfully synthesized from the zinc(II) perchlorate salt by using microwave-heating techniques. In the crystal structure of 1, 4,4′-bipy ligands link trinuclear octahedral Zn(II) building units into rectanglular two-dimensional sheets. The glu2– ligands with anti–anti conformation expand the structure into a cationic rectangular 3D MOF with two crystallographically related perchlorate (ClO4–) counteranions encapsulated in a rectangular {Zn3(4,4′-bipy)4(glu)2}2+ structure as a template of the structure. X-ray diffraction revealed the octahedral to tetrahedral (Znoct–Zntet) conversion upon a ligand-substitution-induced single-crystal to single-crystal (SCSC) transformation of the octahedral Znoct MOF 1 (P1̅); triggering by chloride led to a the 1D-zigzag chain [Zntet(4,4′-bipy)Cl2]n (2; C2/c), triggering by bromide led to a mixed crystalline phase between the isostructural 1D-zigzag chain [Zntet(4,4′-bipy)Br2]n (3;C2/c) and its polymorph, [Zntet(4,4′-bipy)Br2]n (4; P212121), and triggering by iodide led to a 3D-framework [Zntet(glu)]n (5; P21/c). The time-dependent bromide-triggered SCSC transformation was revealed by X-ray diffraction. Photocatalysis for methyl orange degradation of 1 showed that the degradation efficiency reached 14.15% within 300 min under UV-C irradiation.