Synthesis, Structure And Propetries Of Metal-Organic Coordination Polymers Based On The Derivatives Of Imidazoledicarboxylate

With the continuous advancement of technology and society, designing andexploiting new materials has become the most popular research topic in the fieldof chemistry. Metal-organic coordination polymers, as a very important branch inthe field of materials chemistry, has achieved many gratifying results andexhibited very broad potential applications in adsorption, separation, catalysis,sensors, luminescence, optoelectronics and magnetism during the two boomingdecades. The design and synthesis of specific structures is an important part ofsuch materials, in which it is crucial for the choice of ligands. In recent years,substituent modification on the organic ligands, as a effective way to construct aseries of metal-organic coordination polymers with novel structures and uniquefeatures, has attracted great attention of materials chemists. In this paper, weadopted five derivatives of the rigid ligands4,5-imidazole dicarboxylic acid, inwhich the hydrogen on2-position has been replaced by methyl, ethyl,hydroxymethyl, pyridyl and benzoic acid respectively, as ligands to guide thesynthesis of metal organic coordination polymers. Eventually, nine kinds ofstructure, total of fifteen compounds have been prepared and characterized, andall the results are mainly reflected in the following three aspects:1. A series of lanthanide-organic coordination polymers,|(H₂O)₄|[Ln₂(H₂O)₃(HMImDC)₂(OX)](Ln=Sm (1), Eu (2), Gd (3), Pr (4), Nd (5), H3MImDC=2-methyl-4,5-imidazoledicarboxylic acid, OX=oxalic acid), have beensuccessfully synthesized under solvothermal conditions by employing2-methyl-4,5-imidazoledicarboxylic acid and oxalate as mixed organic ligands.Compounds1-5are isostructural and exhibit novel3D architectures which constructed by layers consisted of two type of zigzag chains and dimmersconsisted of lanthanides and [HMImDC]^2-ligands, in addition, there are openchannels of8.9×3.8along a axis. The structural featuers of compound1-5arethat lanthanides linked by [HMImDC]^2-ligands alternately to form a helical chainaround the zigzag chain of Ln-OX, which is rare in the metal-organic coordinationpolymers reported. The same chiral helices are arranged in parallel forming achiral layer, and the enantiomers of chiral layers connect with each otheralternately leading to the formation of3D structure which is racemic. Compounds1-5can be simplified to a4-nodal (3,5)-net, which is a new topological structure,and they are the first lanthanide-organic coordination polymers based onH₃MImDC ligand. Furthermore, compound2exhibits strong red luminescenceemission depending on the characteristic of Eu³⁺ions and compound3showsweak antiferromagnetic interactions by magnetic property investigation. All thecompounds can be stabilized up to350oC and may be used as a potential opticalor magnetic material.2. We take2-ethyl-4,5-imidazole dicarboxylic acid (H₃EImDC) with a longeralkyl chain as organic ligand,2-phenyl imidazole and1,4-Diazabicyclo[2.2.2]octane (dabco) as ancillary ligands, solvothermallysynthesized two1-D chain and2-D layered metal-organic coordination polymers,[Zn(HEImDC)(PhIm)](6) and|DMA|Zn₂(HEImDC)₂(dabco)](7), respectively;and oxalic acid as another auxiliary ligand hydrothermally synthesized three3-Dlanthanide-organic coordination polymers,|H₂O|[Ln2(H₂O)₂(HEImDC)(OX)₂](Ln=Sm (8), Eu (9), Gd (10)). The structure of compounds6and7both consist of[ZnN₃O₂] build units constructed by metal center and H₃EImDC ligands, whichare further connected by H₃EImDC to form a1-D zigzag chain structure. Incompound6, the adjacent zigzag chains connect with each other throughhydrogen-bonding interactions between2-phenyl-imidazoles and carboxylates togenerate a honeycomb-layered supramolecular structure, and compound7has aanalogous honeycomb-layered structure constructed by zigzag chains and dabcomolecules which described by an-AB-sequence along [101] direction. Compounds8-10are crystallography isomorphic and can be described as1Dchains consisted of lanthanide quad-core clusters connect with each other in twodirections through oxalate ancillary ligands forming3D architectures with2-nodal(4,4)-net. In addition, compounds8-10are corresponding to two sets ofopposite chiral helical chains. One set is formed by the connection of-Ln1-OX-Ln2-HEImDC-Ln1-OX-Ln1-, and two enantiomers with helicalcharacters link each other by Ln1-OX-Ln1units; the other formed by-Ln2-OX-Ln1-HEImDC-Ln2-HEImDC-Ln2-and the enantiomers shared withLn2ions. Furthermore, compound9emits intense red luminescence under UVexcitation which exhibit good luminescence properties.3. In order to systematically study the derivatives of4,5-imidazoledicarboxylic acid, we obtain three new ligands with extended substituents:2-(hydroxymethyl)-4,5-imidazoledicarboxylic acid (H4OMImDC),2-(4-pyridyl)-4,5-imidazoledicarboxylic acid (H₃PyImDC) and2-(4-benzoicacid)-4,5-imidazoledicarboxylic acid (H4BCImDC), and take them as bridgingligands successfully preparing five novel metal-organic coordination polymers,|DMF|[Zn₂(H₂OMImDC)₂(4,4'-bipy)](11), Zn3(H₂O)₂(HOMImDC)₂(Im)₂(12),|DMF||H₂O|[Zn₂Mn1.5(H₂O)₂(HOMImDC)₂(Tz)](13), Ni(DMF)₂(HPyImDC)(14)and Cd(H2BCImDC)(15). Compounds11-13use H4OMImDC as the ligands,4,4'-bipyridine, imidazole (Im), and1,2,4–triazole (Tz) as auxiliary ligands,respectively. Compound11is a layered structure constructed from two types ofsix-membered metallocycles, with1-D hexagonal channel along c axis.Compound12is a3-D metal-organic coordination polymer with bto topologyconstructed from zinc ions, H4OMImDC and Im mixed-ligands, which has a rareright-handed chiral spiral tubular channel winded by two left-handed helices, aswell as two sets, total six of right-hand helical chains arranged alternately aroundthe tubular channel. Compound13is based on H4OMImDC as a main ligand, Tzas an auxiliary ligand, through the introduction of Zn²⁺and Mn²⁺ions together tobuild a3-D coordination polymer, and it exhibits good antiferromagneticinteractions. Compounds14uses H₃PyImDC as ligand to form a0-D quadrilateral structure, which connects with the neighbors via hydrogen-bonding interactions toform a2-D supramolecular structure; compound15is a2-D layered structurebased on H4BCImDC, with the hydrogen-bonding interactions between the layers,it can be realized as a3-D supramolecular structure.In summary, we systematically discuss the impacts of the different2-positionsubstituents in4,5-imidazoledicarboxylic acid derivatives on the synthesis ofmetal organic coordination polymers, and successfully prepare a series oftransition metal and lanthanide organic crystal materials with multi-functions suchas luminescence, magnetism and chirality. Furthermore, through the introductionof appropriate ancillary ligands into the synthetic system, the structures of somecompounds can be transformed from0-D to3-D. This work will provide a lot ofvaluable data and information for the design and synthesis of multifunctionalmetal-organic coordination polymers.