Synthesis, Structure And Fluorescence Properties Of Heterocyclic Schiff Bases And Their Transition Metal Complexes

The design, synthesis and properties investigation of functional coordination compounds play an important role in the field of coordination chemistry. The metal complexes containing Schiff bases are the most fundamental investigation systems in coordination chemistry. In the past decades, the heterocyclic Schiff base and their transition metal complexes have attracted a great deal of attention because of their known biological activities and pharmacological properties such as antibacteria, anticancer, anti-inflammatory, antidepressant effects and so on. So it is important for the synthesis and study of functional complexes using the combination of heterocyclic Schiff base multifunctional ligands.In order to further enrich and extend the studies on the functional complexes, such as predetermination of molecular architectures and the properties of the complexes, six novel aromatic heterocyclic Schiff base derivations and their transition metal complexes have been synthesized and characterized by means of elemental analysis, IR spectra, thermal analysis and single crystal X-ray diffraction on the basis of the previous work. The composition and the crystal structures of the compounds were determined. The fluorescence properties of the ligands and the complexes have also been investigated preliminarily. There are five parts in the thesis.1. The development of coordination chemistry and Schiff base complexes were reviewed. The synthesis and application for heterocyclic schiff base ligands and their transition metal complexes were discussed.2. Four new heterocyclic schiff base ligands (L₁-L₄) have been synthesized and structurally characterized by means of elemental analysis, IR spectra, UV-vis, 1H NMR and MS. Three of them were determined by X-ray single crystal diffractions. It is clear that there are one or two imidazolidine rings in the four ligands respectively. It is presumed that nucleophilic attacks lead to the formation of isomers containing saturated heterocyclic rings. Fluorescent properties of the four compounds have been investigated in the solid state at room temperature. Compound L1 exhibits strong fluorescence and thus may be good candidate for green fluorescent materials.3. Transition metal complexes (1-4) with ligand L1 have been synthesized and characterized by means of elemental analysis, thermal analysis, infrared spectroscopy and single crystal X-ray diffraction. It has been observed that the starting ligand cleaved in the forming process of complexes. The methanism of this cleavage is presumed. The driving force for this cleavage may be the hydrolysis catalyzed by transition metal ions according to the correlative references. This hydrolysis action may occur at C=N bond and the transition metal ions may act as Lewis acid to catalyze the reactions. Furthermore, the fluorescence properties of the ligand L1 and complexes were investigated.4. Five complexes (5-9) were synthesized from ligand L3 and transition metal perchlorate, and characterized by means of elemental analysis, infrared spectroscopy, thermal analysis and X-ray single crystal diffraction. The results show that the ligand L3, which was expected to act as tetradentate (N4) chelate to form dinuclear transition metal complex, was found to undergo hydrolytic cleavage of the C=N bond and transformation of the starting Schiff base into the corresponding carboxylate complexes in the presence of transition metal ions. The methanism of this cleavage is presumed.5. The new Schiff base ligands, L₅ and L₆, derived from Quinoxaline-2-carboxaldehyde and 2-phenyl-1, 2, 3-triazole-4-carboxaldehyde with thiosemicarbazide, on refluxing with nickel (II) and zinc (II) acetate in ethanol/THF or ethanol yielded corresponding complexes, respectively. On the basis of elemental analysis and thermal analysis, the metal to ligand stoichiometry of 1:2 has been proposed for these two complexes. The ligand L6 and complex (10) have been structurally characterized by single crystal X-ray diffraction. The ligand L6 and its Zn (II) complex have the good fluorescence activity and may be candidates for fluorescent materials.