Structural Characterization,Spectral Properties And Antimicrobial Activities Of Imidazole Ligands And Their Co(Ⅱ),Cd(Ⅱ),Zn(Ⅱ),Ni(Ⅱ)Complexes

Imidazole ring is a kind of structural unit of complex and natural products and drugs extensively existed in nature.The unique structural characteristics and excellent electron-rich properties of the imidazole ring,which react with metal ions to obtain metal complexes with special properties and various geometrical configurations,which have an extensive range of applications in solar energy conversion and anti-tumor drugs.The numerous complexes containing Co（II）,Cd（II）,Zn（II）,Ni（II）and other metal ions reveal excellent antibacterial properties in the field of biological activity.In this study,several new organic ligands were designed and synthesized,and their properties with Co（II）,Cd（II）,Zn（II）,Ni（II）and other complexes have been investigated.The dominating research contents include the following points:1.Three quinazoline-type ligands were prepared by the reaction of o-aminophenone oxime withimidazol-2-formaldehyde,4-imidazole formaldehyde and4-（diethylamino）salicylaldehyde,respectively.L¹:2-（2-imidazolyl）-4-methyl-1,2-quinazoline-N³-oxide;L²:2-（4-imidazolyl）-4-methyl-1,2-quinazoline-N³-oxide;L³:2-（4-diethylamino-2-hydroxyphenyl）-4-methyl-1,2-dihydroquinazoline-N³-oxide.In addition,the ligand L⁴ of hydrazone containing coumarin ring was synthesized by the reaction of 3-acetylcoumarin and 3-methylbenzoyl hydrazide.Furthermore,the structures of L¹–L⁴are characterized by elemental analysis,¹H NMR,IR.2.Four new complexes were gained by the reaction of ligands L¹ and L²with different metal salts of Co（NO₃）₂·6H₂O,Cd（NO₃）₂·4H₂O,Zn（NO₃）₂·6H₂O and Ni（NO₃）₂·6H₂O,respectively.Complexes 1–4 were obtained by natural volatilization and the structures of complexes were measured and analyzed rely on elemental analysis,spectroscopic methods and single-crystal X-ray diffraction.Co（II）complex 1:[Co（L¹）₂·2CH₃OH]₂·（NO₃）₄,Cd（II）complex 2:[Cd（L¹）₂（NO₃）₂],Zn（II）complex 3:[Zn（L¹）₂·2CH₃OH]₂·（NO₃）₄and Ni（II）complex 4:[Ni（L²）₂]（NO₃）₂·2CH₃OH.The coordination configuration and the supramolecular structure constitute via the intermolecular interactions.3.UV–vis aborption spectra of all complexes and fluorescence spectral properties of complexes 2–4 were analyzed by spectroscopic method,and compared with the corresponding ligands.Moreover,the electrochemical property of Ni（II）complex 4 were also researched.4.The antibacterial activity of 1–4 against Escherichia coli and Staphylococcus aureus were tested by Oxford cup method.The sizes of the inhibition zones exhibited the bioactivity of the compounds against the bacteria.In addition,the structural optimization of all complexes was calculated by density functional theory（DFT）,and the orbital energies of HOMO and LUMO are calculated.Furthermore,the electrostatic potential（ESP）calculations were utilized to analyse electrophilic and nucleophilic attack sites on the molecule,which verified the existence of hydrogen bonds in the optimized crystal structure.Besides,the DFT research has been applied to appraise the noncovalent reciprocities zealously and affirm their vital affect determining the supramolecular structures by Hirshfeld surface analysis and 2-D fingerprinting.