Synthesis And Properties Of Imidazole Dicarboxylic Acid Derivative-based Complexes

The derivatives of imidazole-4,5-dicarboxylic acid containing nitrogen atoms andcarboxyl groups have attracted considerable attention due to their better coordinationactivities and diverstified coordination modes. Twelve coordination compounds based on2-methyl-4,5-imidazoledicarboxylic acid (H3MIDC) and2-ethyl-4,5-imidazolediearboxylicacid (H3EIDC) have been synthesized under hydrothermal/solvothermal conditions andcharacterized by single-crystal X-ray diffraction, Infrared Radiation spectra (IR), CircularDichroism spectra (CD) and thermogravimetric analysis (TGA)，elemental analysis, etc.Moreover, magnetic and luminescent properties of the complexes have also been studied. Themain contents are as follows:Seven compounds based on H3MIDC ligand have been successfully synthesized underhydrothermal/solvothermal conditions, namely,{[Zn3(MIDC)2(4,4’-bpy)3]·(4,4’-bpy)·10H2O}n(1),{[Co3(MIDC)2(4,4’-bpy)3]·(4,4’-bpy)·8H2O}n(2),{[Co3(MIDC)2(py)2(H2O)2]}n(3),{[Mn6(MIDC)4(py)5(H2O)4]}n(4),{[Mn3(MIDC)2(phen)3(H2O)2]}n(5),[Ni(HMIDC)(dpp)]n(6),[Zn(H2MIDC)2(H2O)2](7). Compounds1-5were obtained under the help of N2H4·H2O,however, compounds6and7were obtained as triethylamine act as deprotonating reagent.Interestingly, we found that N2H4·H2O as a deprotonating reagent can effectively control thecoordination mode of H3MIDC ligand. In compounds1-5, the MIDC3-anions all adopt thesame μ3coordination model, and interact with different metal ions and form a similar twodimension (2D) layer of [M3(MIDC)2]. The [M3(MIDC)2](M=Co and Zn) layers wereconneted into a3D metal organic framework with1D channel under the help of the bridgingligand4,4’-bpy as pillars in compounds1and2. The [M3(MIDC)2] layer of1and2seem likea plane. Compounds3and4with2D layers were gained when the capped ligand (py) lie ontwo sides of [M3(MIDC)2] layer, which effectively limited the evolutions of2D [M3(MIDC)2]layer into3D network. Interestingly, there are one and two kind of folders in the2D puckered layer of3and4, respectively. To the best of our knowledge, the complex containing twokinds of folders in a2D layer has not been reported. When chelating phen with strongcoordination activity was introduced into the reaction system, complex5was obtained.Because two nitrogen atoms of the phen ligands occupy one axis position and onecoordination site of equatorial plane, Mn3(MIDC)2in5are different from those of1-4.1exhibits weak blue photoluminescence in the solid state at room temperature.Variable-temperature magnetic susceptibility measurements of2-5indicate strongantiferromagnetic interactions between the metal centers. In compounds6, with the help ofdpp, the HMIDC2-anions jioned NiIIions into a1D framework compounds in a μ2coordinatedmode. Compound7is a mononuclear compound.Five complexes have been obtained based on H3EIDC under mixed reagent ofDMF-H2O-CH3CH2OH, namely,{Co3(EIDC)2(H2O)5}n(8),{Zn3(EIDC)2(H2O)4}n(9),{[Co3(EIDC)2(py)2(H2O)2]·0.5H2O}n(10),[Ni4(HEIDC)4(H2O)8]·2H2O (11),[Co(H2MIDC)2(H2O)2]·DMF (12). Compounds8-10were obtained as N2H4·H2O isdeprotonating reagent, similar with1-5, the same coordination model of H3EIDC were control.When the dpt ligands were added to reaction system,8and9with the homo-chiralframeworks were obtained,8is constructed by left-handedness chiral chains, however,right-handedness chains constitute the homochiral framework of9. Circular Dichroismspectra further confirmed the homochirality of8and9. The topo analysis revealed thatcomplexes8and9display SrSi2topologies. Variable-temperature magnetic susceptibilitymeasurements of8indicate strong antiferromagnetic interactions between cobalt magneticcenters.9exhibits weak blue photoluminescence in the solid state at room temperature. Whenthe triethylamine acts as deprotonating reagent, compound11and12were obtained. In11,HEIDC2-in a μ2coordination mode coordinate with Ni ions to form a zero-dimensional (0D)symmetrical tetranuclear molecular square, and then the squares are joined into an interesting3D supramolecular network by hydrogen bonds.12is a mononuclear compound similar with compound7.