Construction of metal-imidazole-based dicarboxylate networks with topological diversity: Thermal stability, gas adsorption, and fluorescent emission properties

Abstract

Six new metal-organic frameworks (MOFs), namely, [Pb(H 2IDC) 2(H 2O)] n (1), {[Pb(H 2IEDC) 2)]•3H 2O} n (2), [Ca 2(HIDC) 2(H 2O)] n (3), {[Ca 2(IEDC) 2(H 2O) 2]•H 2O} n(4), {[Cd(HIDC)(H 2O)] n (5), and {[Cd 2(HIEDC) 2•3H 2O} n (6) (H 3IDC = 4,5-imidazoledicarboxylic acid, H 3IEDC = 2-ethyl-1H-imidazole-4,5- dicarboxylic acid) were hydrothermally synthesized and characterized. Single-crystal X-ray diffraction shows the ligand H 3IDC is partially deprotonated with H 2IDC - and HIDC 2- forms in three corresponding compounds 1, 3, and 5, meanwhile ligand H 3IEDC also presents different deportonated motifs of H 2IEDC -, IEDC 3-, and HIEDC 2- in 2, 4, and 6, respectively. Moreover, these partially or fully deportonated ligands coordinate in the μ 1 to μ 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 HIDC 2- as a linker and 10-connected tetranuclear metal unit [Ca 4(μ 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 H 3IDC is created. Complex 6 shows a 3D coordination framework containing 1D alternately arranged hydrophilic channels including (H 2O) 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 HIEDC 2- and μ 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. © 2012 American Chemical Society.