Syntheses, crystal structures and UV-visible absorption properties of five metal-organic frameworks constructed from terphenyl-2,5,2',5'-tetracarboxylic acid and bis(imidazole) bridging ligands.

ABSTRACT

The solvothermal reactions of terphenyl-2,5,2',5'-tetracarboxylic acid (H4tptc) and transition metal cations (Ni(II), Mn(II)) afford five novel coordination polymers (CPs) in the presence of four bis(imidazole) bridging ligands (1,3-bimb = 1,3-bis(imidazol-1-ylmethyl)benzene, 1,4-bmib = 1,4-bis(2-methylimidazol-1-ylmethyl)benzene, 4,4'-bibp = 4,4'-bis(imidazol-1-yl)biphenyl, 4,4'-bimbp = 4,4'-bis(imidazol-1-ylmethyl)biphenyl), namely, [M(tptc)(0.5)(1,3-bimb)(H2O)]n (M = Ni for 1, Mn for 2), {[Ni(tptc)(0.5)(1,4-bmib)]·0.25H2O}n (3), {[Ni(tptc)(0.5)(4,4'-bibp)2(H2O)]·2H2O}n (4) and {[Ni(tptc)(0.5)(4,4'-bimbp)(1.5)(H2O)]·H2O}n (5). Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Complexes 1 and 2 are isomorphous and exhibit a 3D (3,4)-connected tfi framework with the point Schläfli symbol of (4·6(2))(4·6(6)·8(3)). Complex 3 shows an unprecedented 3D (4,4)-connected framework with the point Schläfli symbol of (4·6(4)·8(2))2(4(2)·8(4)). Complex 4 displays a novel 2D self-catenating 5-connected network with the Schläfli symbol of (4(6)·6(4)) based on three interpenetrating 4(4)-sql subnets. Complex 5 features a 2D 3-connected 6(3)-hcb network built from interesting chains with loops. To the best of our knowledge, the 3D (4,4)-connected (4·6(4)·8(2))2(4(2)·8(4)) host-framework of 3 and 2D self-catenating 5-connected (4(6)·6(4)) network of 4 have never been documented to date. Moreover, the UV-Visible absorption spectra of complexes 1-5 have been investigated.