Construction of Metal-Imidazole-Based Dicarboxylate Networks with Topological Diversity: Thermal Stability, Gas Adsorption, and Fluorescent Emission Properties

Six new metal-organic frameworks (MOFs), namely, [Pb(H2IDC)(2)(H2O)](n) (1), {[Pb(H2IEDC)(2))]center dot 3H(2)O} (2), [Ca-2(HIDC)(2)(H2O)](n) (3), {[Ca-2(IEDC)(2)(H2O)(2)]center dot H2O}(n) (4), {[Cd(HIDC)(H2O)](n) (5), and {[Cd-2(HIEDC)(2)center dot 3H(2)O} (6) (H3IDC = 4,5-imidazoledicarboxylic acid, H3IEDC = 2-ethyl-1H-imidazole-4,5-dicarboxylic acid) were hydrothermally synthesized and characterized. Single-crystal X-ray diffraction shows the ligand H3IDC is partially deprotonated with H2IDC- and HIDC2- forms in three corresponding compounds 1, 3, and 5, meanwhile ligand H3IEDC also presents different deportonated motifs of H2IEDC-, IEDC3-, and HIEDC2- in 2, 4, and 6, respectively. Moreover, these partially or fully deportonated ligands coordinate in the mu(1) to mu(5) manner to generate one-dimensional (1D) -> three-dimensional (3D) coordination polymers, displaying 10 different coordination modes. Both 1 and 2 have 3D supramolecular networks assembled via hydrogen bonding interactions but different in structure topologies. Complex 1 is a 1D coordination chain and 2 has a two-dimensional (2D) wave layer-like structure with 4(4) topology. Complex 3 is a 3D MOF with 3(10).4(25).5(10) topology built up from linear 2-connected HIDC2- as a linker and 10-connected tetranuclear metal unit [Ca-4(mu(2)-O)(6)] as a node. However, complex 4 presents a 2D MOF with 3(6).4(6).5(3) topology. Different from 3 and 4, with the 4-connected binuclear metal unit [Cd(O-C-O)](2) as a node, a wave-like 2D MOF with 4(4) topology in 5 based on H3IDC is created. Complex 6 shows a 3D coordination framework containing 1D alternately arranged hydrophilic channels including (H2O)(4) clusters and hydrophobic channels partially occupied by ethyl groups from imidazole rings, in which the Cd(II) ion is viewed as a 4-connected node, and HIEDC2- and mu(2)-O are regarded as two different linkers, 6 showing 4(2).8(4) topology. Obviously, these results reveal that the existence of the substitute groups of 2-position in such 4,5-imidazoledicarboxylate ligand plays a critical role in the structural direction of these MOFs. Meanwhile, the adsorption and photoluminescent properties of the selected compounds are investigated.