Studies On Syntheses, Crystal Structures And Properties Of Heterocyclic Ligands And Their Ni(?)?Co(?)?Cu(?) Schiff Base Complexes

Heterocyclic compounds, due to their unique properties, have been occupying a pivotal position in the field of medicine and pesticide. Schiff base ligands have been extensively studied in coordination chemistry mainly due to their facile syntheses, easily tunable steric, well solubility in common solvents and forming stable complexes with most of the transition metals. Particular attention has been devoted to the metal Schiff base complexes in the last two decades and some of which have been shown to exhibit interesting physical and chemical properties. Many complexes of metal ions such as Ni???, Co??? and Cu??? show excellent biological activity and antibacterial activity due to their favorable cell membrane permeability. Moreover, Schiff-base complexes have wide applications in analytical chemistry, catalysis, functional materials and so on.In this paper, seven new heterocyclic ligands have been synthesized. HL₁–HL₄ containing the quinazoline structure and HL₅–HL₇ are straight chain type heterocyclic ligands. The structures of ligands were determined by the method of element analysis and ¹H NMR. The single crystal of ligand HL₇ was obtained. The names of HL₁–HL₇ are following: HL₁: 2-[4-?diethylamino?-2-hydroxyphenyl]-4-methyl-1, 2-dihydroquinazoline 3-oxide; HL₂: 2-?pyridin-4-yl?-4-methyl-1, 2-dihydroquinazoline 3-oxide; HL₃: 2-?3-bromo-5-chloro-2-hydroxyphenyl?-4-methyl-1, 2-dihydroquinazoline 3-oxide; HL₄: 2-?¹H-indol-3-yl?-4-methyl-1, 2-dihydroquinazoline 3-oxide; HL₅: 4-[?furan-2-ylmethylene? amino]-phenyl-ethan-1-one oxime; HL₆: 4-[?thiophen-2-ylmethylene? amino]-phenyl-ethan-1-one oxime; HL₇: 4-{[benzo?d??1,3?dioxol-5-ylmethylene]amino}-phenyl-ethan-1-one oxime.Four new Ni???, Co??? and Cu??? Schiff base complexes were synthesized by ligands HL₁ and HL₃ with Co?CH₃COO?₂·4H₂O?Cu?NO₃?₂·3H₂O?Ni?CH₃COO?₂·4H₂O reaction in an orgnic solvent. The chemical composition and the spatial structure of the crystals were determined by X-ray single crystal diffraction. The complexes are Ni??? complex 1:[Ni?L₃?₂]·2CH₃OH, Co??? complex: [Co?L₃?₂], dinuclear Ni??? complex 2: [Ni?L₁?·?CH₃COO?]₂ and dinuclear Cu??? complex: [Cu?L₁?·?NO₃?]2. The coordination geometries of the metal ions in the four complexes as well as the supramolecular forces inside the crystal are analyzed.The complexes were characterized by IR, UV and fluorescence spectra. The electrochemical properties of the complexes were studied by cyclic voltammetry. Using filter paper diffusion method, the antibacterial activity of the ligands and the corresponding complexes against gram negative bacteria?E. coli? and gram positive bacteria?S. aureus? were determined. The antibacterial activity of the ligand and the complex were compared, and the antibacterial mechanism of the metal complex was also preliminary.