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Synthesis, Characterization and Spectroscopic Studies of Novel Mono and bi Nuclear Zinc(II), Palladium(II) and Cobalt(II) Schiff Base Complexes: Reactivity and Interaction

Askarizadeh, Elham | 2009

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39657 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Mohammadi Boghaei, Davar
  7. Abstract:
  8. Due to study of reactivity and interaction of Schiff base complexes, as models of biological system such as vitamin B (B6 and B12) and enzyme (cytochtome c oxidase), some mono and binuclear Zn(II), Pd(II) and Co(II) Schiff base complexes were synthesized and characterized. As a model for vitamin B6, tridentate Schiff base ligands derived from the condensation of water soluble aldehyde with the amino acids (glycine, L-alanine, L-valine, L-leucine and L-phenylalanine) in the presence of Zn (OAc)2.2H2O give rise to the formation of five new water soluble Zn(II) complexes. The IR spectra of these complexes show that, there are prominent stretching vibration of the azomethine band (HC=N) at 1627-1644 cm-1. The difference between the asymmetric and the symmetric carboxylate stretching frequencies are between 217-235 cm-1 as expected, which implies that the coordination mode of the carboxylate groups could be monodentate. Furthermore, The observed peaks in the 1H NMR spectra of the complexes show the disappearance of the signal due to aldehyde proton (HC=O) at 10.15 ppm, and –OH at 11.4 ppm and appearance of signal in 8 ppm, by which it is suggested the formation of Schiff base moiety of the complexes. In further attempt to study of the model compound of B12, the water-soluble cobalt(II) tetradentate Schiff base complex has been synthesized and characterized. The interaction between imidazole, 1-methyl imidazole and water soluble Schiff base complex are characterized by the appearance of weak electronic absorptions at 454 and 455 nm respectively that are not present in the spectra of the individual reaction partners. Clean isosbestic points are observed at 438 nm and 368 nm, indicating a single equilibrium between two species. The spectral data in several temperatures was used to calculate thermodynamic parameters such as ΔH, ∆S and ∆G. The values of the ΔH are positive for both complexes and show that solvation effect is more effective than the heat of bond formation of the complex. In order to extend improving catalytic activity of Calixpyrrole Pacman complexes as a model of cytochrome c oxidase, under supervision of Dr Jason Love in University of Edinburgh at UK, a new N8 macrocycle Schiff base (H4L2) with sterically rigid fluorenyl back bone was synthesized and characterized. The electrospray mass spectrum of macrocycle showed a parent ion at 905 m/z. x-ray crystallography and other techniques support the formation of the [2+2] condensation product. The [Pd2(L2)] and the air sensitive [Co2(L2)] were also synthesized and characterized. Both of them have Pacman geometry in terms of crystallography data. The presence of eight fluorenyl hydrogens in the 1H NMR spectrum of [Pd2(L2)] suggests that one half of the fluorenyl group are endo- to the molecular cleft, and the others exo. The paramagnetic 1H NMR spectrum of [Co2(L2)] displays 13 signals in the region between 74 and -51 ppm, and the room temperature magnetic moment by Evans’ method support two unpaid electron and Co(II) ions. The [Co2(L2)] reacted with air and produced O2 compound with superoxo and hydroxo bridges, that were fully characterized-structurally. EPR showed 15 lines for superoxo complex with two Co(III) ions. Rotating ring-disk electrochemistry and UV-Vis spectrophotometry method were used to show that these compound can act as a catalyst for reduction of oxygen and also can reduce oxygen to water in a 4-electron,4-proton reduction reaction.

  9. Keywords:
  10. Thermodynamic Parameters ; Water Soluble Schiffbas Complexes ; Pacman Complexes ; Rotating Ring-Disk Electrochemistry

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