Synthesis, Structure And Properties Of Coordination Polymers Based On Imidazoledicarboxylate And Its Derivatives

Coordination polymers are widely recognized as a unique class of novel functional metal-organic materials. They have attracted considerable attention from both the academic and industrial sectors due to their chemical and structural attributes, i.e. flexible tailoring, assortment of topologies and potential applications in gas storage and separation, catalysis, optoelectronics, magnetism, luminescence, sensors, etc.. Remarkable progress has been made in this area since the early 1990s. Nevertheless, the rational design and controlled synthesis of functional coordination polymers possessing unique structures with intended topologies often remains a significant challenge.In this paper, we have prepared ten new coordination polymers using 4,5-imidazoledicarboxylic acid and its derivatives 2-methyl-4,5-imidazoledicarboxylic acid,2-ethyl-4,5-imidazoledicarboxylic acid and 2-propyl-4,5-imidazoledicarboxylic acid as organic ligands under hydrothermal/solvothermal conditions. The topology and properties of these compounds will be discussed. The research presented herein focuses primarily on the following three aspects:(1) Five cobalt zeolite-like compounds with gis topology were assembled from the deliberate construction of functional metal-organic squares (MOSs) as 4-membered ring (4R) building units via directional hydrogen-bonding interactions, |(H2O)28|[Co4(C5HN2O4)4(C3H10N2)4] (1),|(H2O)25|[Co4(C6H3N2O4)4(C3H10N2)4] (2), |(H2O)23|[Co4(C7H5N2O4)4(C3H10N2)4] (3),|(H2O)28|[Co4(C6H3N2O4)4(C2H8N2)4] (4), |(H2O)25|[Co4(C7H5N2O4)4(C2H8N2)4] (5). Note that 4-membered rings are the most abundant secondary building unit (SBU) in traditional inorganic zeolites and MOSs therefore offer great potential to target and construct novel zeolite-like coordination polymers containing 4Rs. In order to construct a suitable functional MOS, we specifically chose to use imidazoledicarboxylate-based ligands as the bridging linker because of their unique potential to offer peripheral uncoordinated oxygen centers when chelated to a metal ion in a N-,O-bis(monodentate) fashion. On the other hand, bis(monodentate) diamines were employed as capping ligands because they introduce additional hydrogen-bonding sites on the periphery of the molecular squares, which are necessary for the assembly of compounds via predictable N-H…O hydrogen bonds.In compounds 1-5, each MOS acts as a finite and rigid supermolecular building block (SBB) which is connected via sixteen hydrogen bonds to four neighboring squares to afford three-dimensional supermolecular networks with the zeolite gis topology. All of these compounds contain one type of cage (a 4684 gis cage enclosed by twenty Co centers) that generates two intersecting orthogonal channels along the a and b axes. Interestingly, each gis cavity in compound 1 encapsulates an unprecedented (H2O)28 water cluster, built from five tetrameric water rings and twelve pentameric water rings, with four additional water molecules on its periphery. Furthermore, each (H2O)28 water cluster is interconnected with four neighboring clusters to generate a three dimensional water network having a diamond (dia) topology. The thermal stability and adsorption properties of this compound are also reported herein.(2) Two novel three-dimensional frameworks |H2O|[Cd3(C5HN2O4)2(H2O)2] (6) and |K|[Cd(C7H5N2O4)] (7) have been hydro thermally synthesized by employing 4,5-imidazoledicarboxylic acid and 2-ethyl-4,5-imidazoledicarboxylic acid as organic ligands, respectively. The topology and thermal stability of both compounds were examined. In compound 6, the adjacent helical chains are connected by theμ5-IDC3-bridges to form a two dimensional layer with Kagome topology. The two parallel adjacent layers are further linked together through the one dimensional chains along the c-axis to construct a three-dimensional framework with a complex hetero 4-,5-, 6-connected net. Compound 7 is a 4-connected three-dimensional framework with pts topology.(3) Three new coordination polymers of varying dimensionality and topology have been prepared and characterized under hydrothermal/solvothermal conditions, |DMF|[Zn2(C7N2O4H6)2(C10N2H8)] (8) and |(H2O)3|[Co(C8N2O4H9)2(H2O)2] (9) and |(H2O)6|[Co5(C5N2O4H)4(C5N2O4H3)2(C12N2H8)4(H2O)2] (10). Compound 8 has been solvothermally synthesized by using 2-ethyl-4,5-imidazoledicarboxylic acid as organic ligand and 4,4'-bipyridine molecule as amine. It is a layered structure described by an -ABC- sequence, which is constructed from two types of six-membered metallocycles. Compound 9 has been hydrothermally synthesized by using 2-propyl-4,5-imidazoledicarboxylic acid as organic ligand, and it presents a three-dimensional supermolecular structure, which are connected by the mononuclear H2O)2] molecules through hydrogen bonds. Compound 10 presents a novel mixed-valence, in which tetranuclear Co3+ squares are tethered into chains by [Co(C5N2O4H3)2(H2O)2] units.In summary, we have prepared a series of coordination polymers using 4,5-imidazoledicarboxylic acid and its derivatives under hydrothermal/solvothermal conditions. The results described herein illustrate the remarkable structural diversity afforded by coordination networks constructed from flexible and multifunctional imidazoledicarboxylate-based ligands. Furthermore, we have investigated the effects of metal ions, organic amines and various synthetic strategies on the structures of coordination polymers.