Syntheses, Structures And Properties Of The Metal–organic Frameworks Of 2-(5-Bromo-Pyridin-3-yl)-imidazole Dicarboxylates

With the development of crystal engineering and supramolecular chemistry, the design and synthesis of metal–organic frameworks(MOFs) have attracted much current attention. In this paper, a new-typed imidazole dicarboxylic acid derivative, 2-(5-bromo-pyridin-3-yl)-1H-imidazole-4,5-dicarboxylic acid(H3L), has been intentionally designed and synthesized, and with this multiple spacer as a main ligand to self-assembly with transition metal ions under hydrothermal conditions twelve coordination polymers with unique structures, namely, [Cd4(HL)4(H2O)6]n(1), [Cd(HL)(DMF)]n(2), [Mn(HL)(C2H5OH)]n(3), [Co2(HL)2(H2O)4]n·3n H2O(4), [Ni2(HL)2(H2O)4]n·3n H2O(5), [Zn2(HL)2(H2O)4]n·3n H2O(6), [Cd2(HL)2(bipy)]n(7), [Co(HL)(bipy)]n(8), [Cd3(HL)3(B-im)2]n?n H2O(9), [Co(HL)(B-im)]n(10), [Ni(HL)(B-im)]n(11) and [Cd(HL)(phen)]n(12) have been synthesized(bipy = 4,4’-bipyridine, B-im = 1,1’-(5-methyl-1,3-phenylene)bis(1H-imidazole), and phen = 1,10-phenanthroline). Those synthesized compounds in this paper were structurally characterized through IR, elemental analysis, powder diffraction, and X-ray single-crystal diffraction analysis.Polymer [Cd4(HL)4(H2O)6]n(1), is a 3D coordination polymer constructed by tetranuclear metal clusters. In this complex, the ligand HL has three coordination modes, and both of ligands and metal ions are three-connected nodes and thereby forming rare structure with {(5,8,12)2(5,12,16)2(5,82)(82,12)} topology. Complex 2 and 3 are 2D isostructural frmaeworks fabricated by the imidazole dicarboxylic acid groups of the ligands HL double chelating metal ions into the right- and left-handed spiral chains which are further linked into meso-polymer with(4.82) topology through the pyridine N atoms of the ligands connecting the right- and left-handed spiral chains. Complexes 4-6 are iso-structural chains. [Cd2(HL)2(bipy)]n(7) is a 3D coordination polymer with a {(4,82)(4,82,103)} topology formed by ancillary ligands bipy bridging together the layers which are formed by ligands HL and metal CdII with a(4,82) topology. [Co(HL)(bipy)]n(8) is a 2D(4,4) grid-like structure formed by the linear polymer chains being linked by the rodlike bridging ligands bipy. With the V-shaped rigid bridging ligands B-im as auxiliary ligands, 2D coordination polymers [Cd3(HL)3(B-im)2(H2O)]n(9) with a novel topology of {(3,4,8)(3,4,5,82,9)2(32,82,92)} and iso-structural 10 and 11 were obtained. In Complexes 10 and 11, two ligands in trans coordination fashion chelate each metal ion, and in this way it bridges metal ions into 21 helical chains. And then V-shaped ligands B-im doubly bridge those opposite chiral helixes to form the(4,6) grids. [Cd(HL)(phen)]n(12) is a 1D chain structure.The analysis of those structures shows that deprotonated ligands H3 L in the twelve coordination polymers exhibit four coordination bridging modes where the imidazole dicarboxylic acid groups of the ligands L display the double chelate bridging mode of μ-k N,O:k N′,O′, showing very interesting coordination orientation. Particularly, this double chelate bridging coordination mode on the formation of the frameworks of those coordination polymers has a significant role. The influence of the other reaction conditions in the process of self-assembly of coordination polymer network structure was further explored. Furthermore, the fluorescence, magnetism and thermal stability of the synthesized complexes have been also studied in-depth in this paper.