Synthesis And Structure Characterization Of Symmetric Schiff Base Complexes

Since the first Schiff base was synthesized in1864, the researches on Schiff base have beenwidely reported both at home and abroad. It was discovered that Schiff base complexes have some uniquefeatures such as redox property, catalytic property, optical property and electrical property, magneticproperty, as well as enzymatic activities related to life. Extensive studies on Schiff bases and theircomplexes have been reported, especially for the Schiff bases of salicylaldehyde and3-carboxylsalicylaldehyde. But the Schiff base of5-methyl-3-carboxylsalicylaldehyde was rarely reported.In view of the reasons, we designed and synthesized the Schiff bases of5-methyl-3-carboxylsalicylaldehyde and their complexes.（1） The complex [Fe（H₂EMS）]0.25H₂O, where H4EMS is the N,N’-bis（5-methyl-3-carboxylsalicylidene） ethylenediamine, was synthesized. The crystal structure of the complex wasdetermined by IR, UV-Vis spectra and X-ray single crystal analysis. The crystal belongs to monoclinicsystem, space group C2/c, cell parameters are: a=2.5977nm（17）, b=1.0490（7） nm, c=1.5071（10） nm, α=90°, β=93.070（13）°, γ=90°, Z=8, M_r=442.72，Dc=1.434g/cm3, F（000）=1828, μ=0.775mm-1, R1=0.0797, wR₂=0.2487. The Fe2+ion is coordinated in a distorted octahedral environment, deviating0.00204nm from the least square plane.（2） The complex Ni（H₂EMS） was obtained by direct synthesis, which was characterized by IR,UV-Vis spectra and X-ray single crystal analysis. The crystal belongs to monoclinic system, space groupC2/c, cell parameter are: a=1.93385（17） nm, b=0.97424（9） nm, c=0.95186（9） nm, α=90°, β=91.084（2）°, γ=90°, Z=4, M_r=441.07, F（000）=912，R₁=0.0352, wR₂=0.0815. The Ni2+ion istetracoordinated in a square planar geometry.（3） Using the liagand H4EMS we obtained the complex Cu（H₂EMS）, its structure was determinedby X-ray single crystal analysis, IR and UV-Vis spectra. Results show that the crystal belongs tomonoclinic system, space group C2/c, cell parameters are: a=1.9292（3） nm, b=0.97450（16） nm, c=0.96552（16） nm, α=90°, β=92.303（4）°, γ=90°, Z=4, M_r=445.90, F（000）=916, R₁=0.0456, wR₂=0.1142. The copper ion is tetracoordinated in a square planar geometry. （4） We synthesized the complex [Fe（HCES）（H₂O）₂], in which H4CES was N,N’-bis（3-carboxylsalicylidene）ethylenediamine. The structure of the complex was characterized by IR, UV-Visspectra, thermal gravimetric analysis, and X-ray single crystal analysis. The Fe3+ion is coordinated by sixoxygen atoms in a distorted octahedral environment, the nitrgeon atom of the ligand was not coordinated.（5） Using5-methyl-3-carboxylsaliclaldehyde,1,10-phenanthroline, we obtained the complex[Cu（phen）（MCS）（H2O）] H2O. The structure of the complex was studied by IR and X-ray single crystalanalysis, the Cu²+ion was pentacoordinated in a tetragonal pyramidal geometry.（6） With ligands deformation as examination index, a theory was established to explaintrans-effect of square planar complexes of d⁸central ions, this theory can independently explain thetrans-effect sequence for all the ligands.