Synthesis, Crystal Structures And Optical Properties Of Bis-Schiff Bases And Their Complexes

Salphen[Salophen,N,N-bis(salicylidene) 1,2-diaminobenzene]-type Schiff bases are bis-Schiff bases with tetradentate coordination and their structures are similar to the porphyrin. Salphen-type Schiff bases have attracted considerable attention of chemists in recent years owing to the special structure.In this thesis, A series of Salphen-type Schiff bases and other bis-Schiiff bases were synthesized by reacting substituted aromatic aldehydes and primary amines under ice bath, four of which were first reported. The chemical structures of these compounds were confirmed by means of IR and 1HNMR.UV absorption and fluorescence spectrum of the compouds were detected in solution and in solid state, and the relationship between the molecule structure and the spectrum was also studied. The results show that an OH group in an ortho-position in the salicylaldehyde is the necessary condition of schiff base compounds which possess strong fluorescence properties. In the polar solvent, the exist of an OH group in an ortho or para position can cause the change of structure of bis-schiff bases; Compared with the solid state, the schiff base's fluorescence is weaker when in the solvent and exhibits emission in the 317nm and 400nm.In this study,5,5'-difluoro—SalphenH2 was synthesized by reactions of the o-phenyldiamine with 5-F-salicylaldehyde under ice bath. Its structure has been investigated by X-ray single crystal diffraction. It reveals that the compound belongs to monoclinic P2(1)/c space group, a =6.0938(8), b=16.347(2), c=94.474(2), V=1651.9(4), Z=4, Dc =1.417 andμ=0.11. The Zn (Ⅱ) complex has also been prepared here and characterized by the analytical and spectroscopic methods. According to the characterization data, the structure of the complex was interpreted and its fluorescence properties were also investigated.Computational chemistry theory is used to explain the bis-Schiff base molecular structure, electronic transition, photochemical properties and intramolecular charge transfer phenomenon. All calculations in this work are carried out using the Gaussian 03 package. Geometries were optimized at the RB3LYP/6-311+G (d.) level. The ground state energy was obtained with RB3LYP method, excited state energy was obtained with RCIS-FC method. The atomic basis set is 6-311+G (d.).Using frontier orbital (HOMO) of ground state and excited states and the moleculal electrostatic potential explain the phenomenon of intramolecular charge transfer of compound e with D-π-A structure.The excited state energy of bis-4-hydroxy-benzaldehyde 1,2-phenyl-enediamine (compound e) obtained with RCIS-FC method is 222.71nm (excited state 4) and 285nm(excited state 1) is very close to the result observed in the UV absorption peak of the experimental values of compound e (ethanol solution),which is 225nm,285nm, respectively. The calculation results are in good agreement with the experimental data.Bis-[2-(2-chloro-4-fluorophenyl)-1H-Benzimidazole]-hydrate has been synthesized from bis-Schiff base. The results determined by XRD reveals that the complex crystallizes in Triclinic, space group P1, with a = 7.592(2), b=7.595(2), c=11.886 (3) A, K=574(3) A3, Mr=352.33, Dc = 1.478g/cm3,μ(MoKa)= 0.33 mm-1, F(000)= 262, Z=1, the final R= 0.090 and wR=0.209. The crystal structure is formed with two benzimidazole molecules, which are linked by a water molecule as center, similar to the complex of benzimidazole. The reaction mechanism was also discussed by changing reaction conditions. It is demonstrated that benzimidazole can only be formed from Schiff base effectively when o-hydroxyl group does not exist in benzaldehyde.Detailed crystallographic analyses of the compounds were carried out. The intramolecular or intermolecular hydrogen bonds are existed in the supermolecular structures,π-πinteraction is existed in the crystal structure of 5,5'-difluoro-SalphenH2.