Synthesis,Structure And Fluorescence Properties Of D¹⁰ Imidazole Dicarboxylic Acid Complexes

d¹00 metal complexes of nitrogen heterocyclic exhibit excellent performance in area like light emission,catalysis,biomedicine and identification,therefore widely applicated in the fields of environment,medicine and biology,especially in terms of fluorescent properties,the luminescence of which has significant response to external environmental stimuli and has strain,attracting considerable attention as fluorescent materials.Therefore,it is of great significance to develop d¹00 metal complexes of nitrogen heterocyclic with novel structure and good performance.In this paper,two nitrogen heterocyclic ligands 4,5-imidazole dicarboxylic acid（H₃IDC）,1,4-[bis（2,2’-benzimidazole）]butane（BBM）,were reacted with d¹00 metal（Zn（II）,Cd（II）,Ag（I））to prepare six novel nitrogen heterocyclic complexes.Moreover,an organic ion salt was prepared by reacting 1,4-[bis（2,2’-benzimidazole）]butane（BBM）with nitric acid.The above nitrogen heterocyclic complexes were characterized by elemental analysis,infrared,and X-ray single crystal diffraction,and the photoluminescence and electrochemical properties of the complexes were studied,and the specific research contents are as follows:1、The research progress of d¹⁰metal complexes of 4,5-imidazole dicarboxylic acid has been introduced.2、4,5-imidazole dicarboxylic acid（H₃IDC）or 1,4-[bis（2,2’-benzimidazole）]butane（BBM）was selected as ligands.Four complexes,as follows:[Cd8Li2（H2IDC）6（HIDC）6]（1）,[Cd₂（H₂IDC）₄（BBM）]_n（2）,[Zn₂（H₂IDC）₄（BBM）]_n（3）,[Cd（H₂IDC）₂（H₂O）₃]·H₂O（4）were prepared with hydrothermal or ether diffusion and characterized by elemental analysis,infrared,and single crystal diffraction.The X-ray diffraction studies reveal that complex 1 is an eight-core cage-like cluster compound,2 is a three-dimensional coordination polymer,3is a two-dimensional coordination polymer,and 4 is a single-nuclear complex.Eight cadmium ions in complex 1 occupy the apex of the cube,forming a cage-shaped cube cluster,two lithium ions are distributed inside and outside of the cage,each cadmium ion is a six-coordinate twisted octahedron geometry Complex 4 is a mononuclear complex formed by three coordinated waters and two 4,5-imidazole dicarboxylic acids,of which cadmium ion is a seven-coordinated twisted pentagonal double cone configuration.The main and secondary ligands of complexes 2 and 3 are the same,and different structures are formed due to different central ions.A three-dimensional polymer is formed when cadmium is the central ion,whereas,a two-dimensional polymer is formed when zinc is the central ion,may be due to the radius of the central ion therefore forming different structures.The fluorescence properties in the solid state show that the ligand 4,5-imidazole dicarboxylic acid has two strong fluorescence peaks（420 nm,435.8 nm）,which can be assigned to（π*-n andπ*-πtransitions）.Complexes 1-4 showed two fluorescence peaks of the ligand,compared to the ligand,the cadmium complex produces a small displacement,while the zinc complex is significantly blue-shifted,and the fluorescence intensity of the complex is stronger than that of the ligand,may owing to ligand participating in coordination with central metal ion and the backbone of the ligand is fixed,which reduces the vibration energy loss of the ligand.3、Two kinds of new silver coordination polymers[Ag₂（o-coumarate）₂（4,4’-bipy）₂]_n（5）and[Ag₂（H₂IDC）₂（NH₃）₃]_n（6）were prepared by reacting the ligand 4,5-imidazole dicarboxylic acid（H₃IDC）or o-coumarate with silver oxide through interface reaction or natural volatilization method.The X-ray diffraction studies shows that the central ion silver in complex 5 is first bridged with 4,4’-bipyridine to form a linear single chain,and then the silver in the two single chains is bridged by the carboxyl group of o-hydroxycinnamic acid.Formation of one-dimensional double-chain polymers Complex 6 is a one-dimensional polymeric chain bridged by silver and 4,5-imidazole dicarboxylic acid to form a ladder-like ring,including a linear tetranuclear silver cluster Most importantly,there is a strong Ag-Ag interaction for both complexes 5 and 6.The fluorescence properties in the solid state indicate that the fluorescence of the coordination polymers 5 and 6 with respect to the ligand both partially quenched,mainly due to the heavy atom effect of silver and Ag-Ag interaction.Electrochemical cyclic voltammetry studies have shown that there is a reversibly aligned redox peak for complexes 5 and 6.4、An organic benzimidazole ion salt（H₂BBM）₂·（NO₃）₂ was prepared by the reaction of1,4-[bis（2,2’-benzimidazole）]butane（BBM）with nitric acid.The X-ray diffraction studies shows that the main structure of the organic ion salt is formed by two imidazole cations and two counter anions（NO₃^-）.The analysis of fluorescence experiment in solid state shows that a fluorescence quenching phenomenon appeared compared with the ligand,which can be mainly attributed to the protonation of the reaction between the imidazole and the acid,leading to the reduction of the conjugation of the imidazole and thus the fluorescence quenching.