Oxygen Affinity of the Transition Metal Complexes Of Schiff Base Ligands

1. Oxygen Affinity of the Transition Metal Complexes Of Schiff Base Ligands متراكبات العناصر الإنتقالية لليجاندات قواعد شيف الحاملة للأكسجين Adel A.A. Emara Associate Prof. in Inorganic Chemistry University Collage in Mekkah Umm Al-Qura University

2. Outlines • 1- Historical Background. • 2- Natural Biological Oxygen Carrier Metal complexes. • 3- Criteria for the Schiff base complexes to carry oxygen. • 4- (a) Schiff base ligands, (b) metal complexes of the • Schiff base ligands. • 5- Characterization of the ligands and their metal • complexes. • 6- Study of the absorption and desorption of the metal • complexes in strong and weak polar solvents. 7- Conclusions.

3. 1- Historical Background • In 1852: Fremy reported that the exposure of ammoniacal solutions of Co(II) salt to the atmosphere resulted in the formation of brown salts which he called oxo-cobalates. • In 1898: Werner characterized the compounds as containing the diamagnetic cation [(H3N)5Co(O2)Co(NH3)5]4+. • In 1938: Tsumaki made the first report of a synthetic reversible cobalt-oxygen carrier. • World War II: U.S. Navy used these complexes in the production of pure dioxygen in a destroyer tender for use in welding and cutting. Also, they used the complexes in the aircraft crew. • In 1978: Floriani studied the behavior of derivatives of [Co(II)salen] in non aqueous media and found, in general, the ratio uptake of O2 : Co(II) is 1 : 2. • In 1985: When pyridine solutions of [Co(3-methoxy-salen)] were exposed to O2 at 10°C, an O2 uptake : Co(II) is 1 : 1 was observed. Heating the dioxygen adduct in vacuo regenerated the starting material.

4. 2-Natural Biological Oxygen Carrier Metal complexes

5. R = -CH=CH2 : Protoporphyrin IX R = CHO : Chlorocruoroporphyrin The numbers: methyl; vinyl; Propionic acid; ethyl or Phenyl substituents. α, β, γ and δ position have the same substituent. Figure 1. Structures of natural and synthetic porphyrins.

6. 3- Criteria for the Schiff base complexes to carry oxygen: • i) The Schiff base complexes of the Co(II), Ni(II) and Mn(II) metal ions form: (a) square planar arrangement with tetradentate Schiff base ligands, or (b) square pyramid arrangement with pentadentate Schiff base ligands. • ii) The complexes should be soluble in suitable non-aqueous solvent.

7. 4- Synthesis of Schiff base ligands and their transition metal complexes • (a) Schiff Base Ligands The condensation reaction between aldehydes or ketenes with primary amines.

8. Aldehydes and ketones Amines

9. Tetradentate Ligands Pentadentate Ligands Ligand R1 R2 ๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘ ๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘ ๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘ (D) H2Saldet H o-OHC6H4- (E) H2o-Hacdet CH3o-OHC6H4- (F) H2Acacdet CH3 -CH=C(OH)CH3 Figure 2. Representative structures of Schiff base ligands

10. B) Metal Complexes of the Schiff Base Ligands Abs. Ethanol M(II) salt + Schiff base ligands [ML] Complex Square planar or M(II) = Co(II), Ni(II) and Mn(II) Square pyramid

11. Adel A.A. Emara, A.M. Ali, E.M. Ragab and A.A. El-Asmy; J. Coord. Chem., 61, 2968-2977 (2008).

12. Adel A.A. Emara, A.M. Ali, A.A. El-Asmy and E.M. Ragab; Brazilian Chemical Society, in press.

13. Figure 3. Glove bag flushed with dry nitrogen gas used for handling the starting materials and equipments.

14. Figure 4. Purification of N2 gas. (A) Pyrogallol in ethanol, (B) Sodium hydroxide pellets, (C) Silica gell, (D) solid calcium chloride and (E) to the glove bag.

15. Figure 5. Reaction vessels used in synthesis of square planar and square pyramide Schiff base metal(II) complexes.

16. 5- Characterization of the Schiff base ligands and their Co(II), Ni(II) and Mn(II) complexes The used techniques are: • Elemental (C, H and N) analyses. • Metal ions analyses using EDTA. • 1H-NMR spectra of the ligands. • Melting points. • Mass spectra. • Infrared spectra. • Electronic spectra. • Magnetic measurements. • Molar conductivity measurements. • Thermal gravimetric analysis (TGA).

17. Table 1. Physical and analytical data of the synthesized ligands and Schiff base complexes under nitrogen atmosphere. *. Oily product and the elemental analysis was not performed.

18. Table 2. Characteristic vibrational bands (cm-1) of the Schiff base, ligands and their Co(II), Mn(II) and Ni(II) pentadentate complexes under nitrogen atmosphere.

19. Table 3. Electronic spectral bands magnetic moments and molar conductivity of the prepared Schiff base metal complexes. (a) The type of transition was not assigned. (b) No values were obtained. (c) Values were measured in DMF solution. (d) Complexes prepare in air atmosphere. (e) Complexes prepared under dry nitrogen atmosphere.

20. dx2-y2 dx2-y2 eg dz2 t2g dz2 dxy dxy eg t2g high spin tetrahedral dxz dyz dxz low spin octahedral high spin octahedral low spin square pyramid dyz low spin square planar Figure 6. Energy level diagram of cobalt(II)(d7) ion in high-spin tetrahedral, octahedral (high and low-spin), square pyramid (low spin) and low-spin square planar.

21. TGA analysis Figure 7. TGA and DrTGA of the [Mn(o-Hacdet)].

22. Structure 3. Square planar Schiff base complexes; M = Co(II), Ni(II) or Mn(II).

23. Structure 4. Square pyramide of the [Co(saldet)] Structure 5. Square pyramid structure of the nitrato complexes [M = Ni(II) or Mn(II)].

24. 6- The Oxygen Sorption Process of the Metal Complexes of the Schiff Base Ligands n[ML] + O2⇋ [ML]n(O2) where n = 1 or 2 In (a) suitable solvent and (b) controlled temperature.

25. Solubility in DMF and chloroform Table 4. Solubility of Co(II), Ni(II) and Mn(II) pentadentate Schiff Base complexes in DMF and chloroform solvents at 25 °C. It is important to know the maximum solubility of each complex, which is an important parameter. This solubility parameter could give us the highest capacity of each Schiff base complex solution to carry oxygen.

26. Figure 8. Measurement system for the absorption and desorption of the Schiff base complexes with oxygen. (A) nickel-monel vacuum line, (B) gauge for measuring the absorption and desorption of oxygen, (C) the reactor, (D) solvent trap, (E) valve, (F) thermometer (–40 to 40 °C), (G) thermometer (0 to 120 °C), (H) water and (I) dissolved oxygen meter.

27. Table 5. Oxygen absorption capacity of cobalt(II) Schiff base oxygen carrier in 100 mL DMF from -5 ºC (absorption) to 100 ºC (desorption).

28. Table 6. Oxygen absorption capacity of cobalt(II), nickel(II) and manganese(II) pentadentate Schiff base oxygen carrier in 100 mL DMF and chloroform solvents from -5 ºC (absorption) to 100 ºC (desorption).

29. oxygen concentration: is considered the amount of oxygen measured by the dissolved oxygen (D.O.) meter, which indicate the molar ratio of the complex carrier to the oxygen carried in the complex. • Carrier loading % [(Carrier complex)] + O2 carried  [(Carrier complex)O2] Mole of O2 carried Carrier loading % =  x 100 Mole of [(Carrier complex)O2] The oxygen capacity: is the weight of oxygen molecules carried by the carrier complex.

30. Table 7. Oxygen absorption capacity of cobalt Schiff-Base complex, [Co(Saldet)], oxygen carrier in 100 mL DMF from -5 ºC (absorption) to 100 ºC (desorption) in different concentrations.

31. 7- Conclusion • After the study of the absorption and desorption of the Co(II), Ni(II) and Mn(II) tetradentate and pentadentate Schiff base complexes. It is clear that: • Co(II) Schiff base complexes behave as good oxygen carriers than Ni(II) and Mn(II) Schiff base complexes. • Co(II) pentadentate Schiff base complexes is more effective as oxygen carriers than the Co(II) tetradentate Schiff base complexes. • This kind of materials can be used as catalysts in oxidative addition reactions in the organic chemistry and petrochemicals, which is reproducible and not polluted like other oxidants which is considered that this materials as friendly to the environmental.