Six new metal-organic frameworks with multi-carboxylic acids and imidazole-based spacers: syntheses, structures and properties.

Six new metal-organic frameworks Cu(obba)(bimb)·(obbaH(2)) (1), Cu(obba)(bimb) (2), Zn(2)(obba)(2)(bimb)(2)(DMF)(2)(H(2)O)(3.5) (3), Ni(3)(2,2',4,4'-bptcH)(2)(bimb)(2)(H(2)O)(2)·(H(2)O)(2) (4), Ni(2)(bimb)(3)(H(2)O)(6)·(aobtc)·(DMF)(2)·(H(2)O)(2) (5) and Cd(3,3',4,4'-bptcH(2))(H(2)O)·(bimb) (6), were obtained by reactions of 4,4'-bis(1-imidazolyl)biphenyl (bimb) and multi-carboxylic acids of 4,4'-oxybis(benzoic acid) (obbaH(2)), 2,2',4,4'-biphenyltetracarboxylate acid (2,2',4,4'-bptcH(4)), azoxybenzene-3,3',5,5'-tetracarboxylic acid (aobtcH(4)), and 3,3',4,4'-biphenyltetracarboxylate acid (3,3',4,4'-bptcH(4)) with corresponding metal salts under hydro/solvothermal conditions, respectively. Complexes 1-3 have entangled structures with different topologies: 1 is a 3-fold interpenetrating NbO three-dimensional (3D) network; 2 is a 3-fold interpenetrating dmp 3D net; 3 is a 6-fold interpenetrating dia 3D chiral net containing rare 1D helical chains with the same handedness. Complex 4 is an uninodal 6-connected network with a Schäfli symbol of (4(8)6(4)8(3)) based on the trinuclear Ni(II) subunits, while complexes 5 and 6 are 1D chains. Interestingly, compound 6 represents the rare example of MOFs that exhibit high photocatalytic activity for dye degradation under visible light and shows good stability towards photocatalysis. Complexes 3 and 6 exhibit intense blue emissions in the solid state at room temperature whereas 3 appears to be a good candidate of novel hybrid inorganic-organic NLO material.