Synthesis, Characterizations And Properties Of Chiral Unsymmetric Schiff Base And Cu-Ln Complexes

Schiff base is a sort of important organic compounds, whose structures are tunable by the substituents in the corresponding aldehydes and amines. More and more novel Schiff bases were synthesized due to their extensive applications in the fields of catalysis, biochemistry and functional materials, to mention but a few. Recently, novel unsymmetric chiral Schiff bases and their complexes as well as polynuclear, heteronuclear Schiff base complexes have received much attention.Chirality is a term in stereochemistry that describes the 'handeness' of a molecule. Chiral molecules have a degree of asymmetry that makes their mirror images non-superimposable. Study on chiral Schiff base metal complexes plays an important role in the research on chirality. Therefore, discussion on relation between the structures and properties of chiral Schiff base complexes is valuable for designing chiral drugs, functional materials, and exploring the mechanism of asymmetric catalysis.Circular dichroism (CD) spectroscopy as an especial technique of fingerprint has all along played an important role in characterization of chiral metal complexes, which can provide useful information on the absolute configuration and conformation of chiral molecules, enantiomeric excess of the chiral substances. As a major tool in chiral solid-state chemistry, solid-state CD is currently attracting a great deal attention since it should provide invaluable information unobtainable from solution CD; for example, of particular interest is an unusual conformation of chiral molecules that is unstable in solution. Combining CD with UV-Vis spectra and other structural analysis including X-ray crystallographic data may gain a comprehensive insight into the details of the structural features, electronic levels and electronic transitions of chiral metal complexes.The main results in this dissertation are obtained as follows:1. A series of novel unsymmetric chiral Schiff bases and their Ni(II) complexes with related structures were designed, synthesized and characterized respectively by UV-Vis, IR, CD, ¹H NMR spectra and elemental analysis. Some stereoselective synthetic methods of chiral Schiff base complexes were discussed through an in-depth study on the experiment results. The CD spectra of unsymmetric chiral Schiff bases Ni(II) complexes were compared with those of symmetric ones, whose crystal structures were solved by X-ray single crystal diffraction in the noncentrosymmetric space group P2₁2₁2₁. In the case of four-coordinated pseudo-planar Ni(II) complexes we therefore have the following empirical rules: (i) (S)Δλfor the complexes derived from S-pn and S,S-dpen, which are reflected by the positive Cotton effects at about 550 nm in the d-d region; and (ii) (S)Λδfor the complexes derived fromS,S-chxn with a concomitant inversion of the Cotton effects. This is available for both unsymmetric and symmetric chiral Schiff bases complexes of similar structures.2. It has been observed by the antimicrobial activity studies that all the tested chiral Schiff bases and their complexes inhibit tested Staphlococcus aureus. The antimicrobial activity was related with the spatial and chiral structures of the compounds, and unsymmetric chiral Schiff base complex has much higher activity than its related symmetrical one against the same bacteria under identical experimental conditions.3. Some novel chiral hetero-dinuclear (Cu-Ln) Schiff base complexes (Ln = Gd, Sm, La) with related structures were designed, synthesized and characterized respectively by UV-Vis, IR, CD spectra and elemental analysis. It is notable that there is some difference between the solid-state and solution CD spectra of the selective chiral heterobimetallic complexes measured. This may be described to some subtle conformational distinctions between the two states.