Syntheses, structural diversity, magnetic properties and dye absorption of various Co(II) MOFs based on a semi-flexible 4-(3,5-dicarboxylatobenzyloxy)benzoic acid

Five novel Co(II) metal-organic frameworks (MOFs) constructed from semi-flexible 4-(3,5-dicarboxylatobenzyloxy) benzoic acid (H3L), namely {[Co-1.5(HL)(4,4'-bidpe)(2)(H2O)]center dot 3H(2)O}(n) (1), {[Co-3(L)(2)(4,4'-bibp)(3)(mu(2)-O)(2)]center dot 2H(2)O}(n) (2), {[Co(HL)(1,3-bitl)]center dot(1,4-Diox)}(n) (3), [Co-2(HL)(2)(3,5-bipd)(2)](n) (4), and {[Co(HL)(tib)] center dot 0.5H(2)O center dot NMP}(n) (5) (4,4'-bidpe = 4,4'-bis(imidazolyl)diphenyl ether, 4,4'-bibp = 4,4'-bis(imidazol-1-yl) biphenyl, 1,3-bitl = 1,3-bis(1-imidazoly)toluene, 3,5-bipd = 3,5-bis(1-imidazoly)pyridine, and tib = 1,3,5-tris(1- imidazolyl)benzene), were synthesized under solvothermal conditions and further characterized by elemental analysis, IR spectra, powder X-ray diffraction (PXRD), thermogravimetric (TG) analysis and single-crystal X-ray diffraction. Different architectural topologies have been generated by adjusting the N-donor ligands. Single-crystal X-ray diffraction analysis reveals that complex 1 shows a rare 1D -> 2D polyrotaxane network. Complex 2 possesses an unprecedented 2-nodal (3,10)-connected 3D framework with a Schlafli symbol of (4(3))(2)(4(6).6(32).8(3))(4(3))(2). When the 2-connected points (H3L and 1,3-bitl ligands) are not calculated, complex 3 shows a hcb uninodal 3-connected 2D network with the Schlafli symbol (6(3)), which further constructs a 3D supramolecular structure through O-H center dot center dot center dot O hydrogen bonds; while the 2-connected points are taken into account, complex 3 exhibits an unprecedented 3-nodal (2,2,4)-connected network. Complex 4 presents an unprecedented 2-nodal (3,5)-connected 3D framework with a (4.6(2))(4.6(6.)8(3)) topology, while complex 5 exhibits another unprecedented 2-nodal (3,5)-connected 2D framework with a (4(2).6(7) .8)(4(2).6) Schlafli symbol and shows 2D -> 3D supramolecular structure through O-H center dot center dot center dot O hydrogen bonds. Meanwhile, the magnetic properties of complexes 2 and 4 are discussed. Moreover, the dye adsorption and mechanism studies indicate that the pore size, the uncoordinated O atoms in carboxyl groups and the uncoordinated carboxyl groups of the MOFs have significant effects on the dye adsorption capacity.