Ionothermal Synthesis of Five Keggin-Type Polyoxometalate-Based Metal-Organic Frameworks.

Five unique Keggin-type polyoxometalate (POM)-based metal-organic frameworks (POMFs), namely [CHL1][(CuL1)(PMoMoO)] (1), [Zn(HO)(L1)][Zn(L1)Cl][HL1][PMoO]·1.25HO (2), (TBA)[Cu(HO)L1][PMoO] (3), [Cu(HO)(L1)][PMMoO] (4), (HL2)[(CuL2)(PMoO)]·HO (5), L1 = 4,4'-bis((1H-1,2,4-triazol-1-yl)methyl)-biphenyl, L2 = 1,4-bis((1H-1,2,4-triazol-1-yl)methyl)-benzene, have been synthesized under ionothermal conditions. According to single-crystal data, 1 exhibits a novel mechanically interlocked molecular architecture (MIMA) constructed by two-dimensional (2D) interpenetrating polyrotaxane layers with unique cyclophanes (tetra-cationic viologen macrocycle cyclobis(paraquat- p-phenylene) (CBPQT system)), resulting in an H-bonded 3D supermolecule, and is the first synthesis of self-assembled cyclophane-PMOFs under ionothermal conditions. 2 shows a novel 2D three-fold interpenetrating polyrotaxane host and guest network. 1 and 2 are presented as the first MIMA polyrotaxane structures to have been synthesized under ionothermal conditions. Electrochemical impedance spectroscopy (EIS) reveals that 2, 4, and 5 show high proton conductivity owing to their unique structural properties. Solid-state diffuse reflection UV-vis-NIR measurements show the title compounds are potentially semiconductor materials. Photocatalytic investigations indicate that 1-5 possess high and stable photocatalytic H evolution and rhodamine B (RhB) degradation under visible-light irradiation.