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. قالوا سبحانك لا علم لنا إلا ما علمتنا إنك أنت العليم الحكيم
صدق الله العظيم

3. 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.

4. 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.

5. Location Source Metal Protein
2-Natural Biological Oxygen Carrier Metal complexes
Location
Source
Metal
Protein
Corpuscles
Mammals
Birds
Fish
Insects
Fe (heme)
Hemoglobin (Hb)
Muscle
Other vertebrates
Some invertebrates
Myoglobin (Mb)
Plasma
Snails
Lugworm
Earthworm
Erythrocruorin (Ery)
Marine worms
Chlorocruorin (Chl)
Fe (non-heme)
Hemerythrin (Her)
Mollusks
Arthropodes Cu
Hemocyanin (Hcy)
Ascidians V
Hemovanadin (Hv)

6. Figure 1. Structures of natural and synthetic porphyrins.
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.

7. 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.

8. 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.

9. Aldehydes and ketones
Amines

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

11. 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

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

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

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

15. Figure 4. Purification of N2 gas
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.

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

17. The used techniques are:
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).

18. Elemental analysis % Found/(Calcd)
Table 1. Physical and analytical data of the synthesized ligands and Schiff base complexes under nitrogen atmosphere.
Elemental analysis % Found/(Calcd)
m.p.,
(C)
Yield,
(%)
Color
M.F.
Formula
Ligands and Complexes M N H C ——
12.23
(12.38)
7.37
(7.42)
71.05
(70.77)
105 92
Golden yellow
339.44
C20H25N3O2
[H2o-Hacdet] 85
Reddish brown
311.38
C18H21N3O2
[H2Saldet] *
10.23
(10.19)
12.12
(12.16)
5.68
(5.42)
41.84
(41.69)
235 87
Pale orange
576.18
C20H31N5O11Ni
[Ni(H2o-Hacdet) (NO3)2]
13.63
(13.34)
9.63
(9.55)
5.97
(6.13)
49.64
(49.12)
250 77
Orange
440.12
C18H27N3O6Ni
[Ni(Saldet)]
13.10
(13.39)
9.38
(9.54)
6.03
49.17
(49.10)
290 83
Pale brown
440.30
C18H27N3O6Co
[Co(Saldet)]
12.03
(12.11)
7.56
(12.36)
5.05
(4.96)
48.68
(48.80)
>300 76
Dark green
443.33
C18H22N4O6Mn
[Mn(HSaldet)(NO3)2]
11.25
(11.64)
9.52
(9.06)
6.39
(6.68)
51.54
(51.72) 74
464.11
C20H31N3O6Mn
[Mn(o-Hacdet)]
*. Oily product and the elemental analysis was not performed.

19. 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.
ν(M-O)
ν(M-N)
ν(C-N)
ν(C-O)
ν(-C=N-)
ν(CH3)
ν(=C-H)
Ligands and complexes ——
1338 m
1278 vs
1632 vs
2846 s, br
3056 m, br
[H2Saldet]
1326 m
1242 m
1614 vs
2914 w, br
3058 w, br
[H2o-Hacdet]
323 w
475 w
1384 vs
1202 w
1628 m
[Co(Saldet)]
306 vw
564 w
1398 m
1204 m
1624 vs
2924 m, br
3040 m, br
[Mn(HSaldet)(NO3)]
375 m
446 vs
1326 vs
1236 vs
1643 s
2926 m, br
3063 m, br
[Mn(o-Hacdet)]
345 w
454 vw
1240 m
1610 m
2866 m, br
3040 w, br
[Ni(H2o-Hacdet)(NO3)2(H2O)]
305 vw
433 w
1199 m
2938 m, br
3052 m, br
[Ni(Saldet)]

20. Molar conductivity (c) Electronic Transitions (nm)
Table 3. Electronic spectral bands magnetic moments and molar conductivity of the prepared Schiff base metal complexes.
Molar conductivity (c)
Magnetic moment
(B.M.) (b)
Electronic Transitions (nm)
d-d transitions (a)
Complex 18 ——
569 (0.064)a
[Ni(H2o-Hacdet)(NO3)2] .2H2O(e) 9
578 (0.015)a
[Ni(Saldet)] (e) 22
2.43
600 (0.04), 412 (0.26),
700 (0.36)
[Co(Saldet)].4H2O (e) 13
1.73
470 (0.06)
[Mn(HSaldet)(NO3)](d) 15
449 (0.05)
[Mn(o-Hacdet)] (e)
(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.

21. low spin square pyramid
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.

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

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

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

25. n[ML] + O2 ⇋ [ML]n(O2) where n = 1 or 2
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.

26. Solubility (M) Chloroform DMF 0.10 0.11 0.15 0.08 0.09
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.
Solubility (M)
Complex
Chloroform
DMF
0.10
0.11
[Ni(Saldet)]
0.15
[Co(Saldet)]
0.08
0.09
[Mn(o-Hacdet)]
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.

27. 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.

28. Table 5. Oxygen absorption capacity of cobalt(II) Schiff base oxygen carrier in 100 mL DMF from -5 ºC (absorption) to 100 ºC (desorption).
Average carrier loading (%)
Carrier loading
(%)
Oxygen capacity
(x10-4 g)
Oxygen conc.
(x 10-3 M)
Cycle number
Axial base Conc.
(×10-2 M)
Carrier conc.
Carrier
8.02
8.34
7.49
9.17
7.09
3.13
2.81
3.44
2.66
10.00
9.00
11.00
8.5 1 2 3 4
None
[Co(o-Hacen)]
8.44
7.59
9.22
7.11
Pyridine
9.46
11.17
3.75
4.19
12.00
13.00
9.60
[Co(Acacen)]
9.43
9.18
11.21
7.25
13.40
9.23
8.18
11.11
9.42
2.72
3.53
8.70
11.30
[Co(Salen)]
9.26
9.19
7.31
9.44
3.43
4.06

29. Average carrier loading (%)
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).
Average carrier loading (%)
Carrier loading
(%)
Oxygen capacity
(x 10-4 g)
Oxygen conc.
(x 10-3 M)
Cycle number
Solvent
Carrier conc. (×10-2 M)
Carrier
11.08
12.50
12.08
10.58
9.17
4.69
4.53
3.97
3.44
15.00
14.50
12.70
11.00 1 2 3 4
DMF
[Co(Saldet)]
6.00
6.42
6.66
5.33
5.57
2.41
2.50
2.00
2.09
7.70
8.00
6.40
6.70
Chloroform
10.0
3.75
4.43
4.00
3.57
3.01
1.66
1.50
1.34
1.13
5.30
4.80
4.30
3.60
11.0
[Ni(Saldet)]
3.21
3.41
2.83
1.28
1.06
4.10
3.40
4.11
4.59
3.49
1.72
1.31
5.50
4.20
9.00
[Mn(o-Hacdet)]
4.16
3.17
1.56
1.19
5.00
3.80

30. 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.
The oxygen capacity: is the weight of oxygen molecules carried by the carrier complex.
Carrier loading %
[(Carrier complex)] + O2 carried  [(Carrier complex)O2]
Mole of O2 carried
Carrier loading % =  x 100
Mole of [(Carrier complex)O2]

31. Average carrier loading (%)
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.
Average carrier loading (%)
Carrier loading (%)
Oxygen capacity
(x10-4 g)
Oxygen conc.
(x 10-3 M)
Cycle number
Carrier conc.
(×10-2 M)
Carrier
6.87
6.58
7.14
7.25
6.50
2.47
2.68
2.72
2.44
7.90
8.60
8.70
7.80 1 2 3 4
9.00
[Co(Saldet)]
6.25
5.68
6.00
6.74
2.13
2.25
2.53
6.80
7.20
8.10
5.71
6.16
5.44
4.82
6.42
2.31
2.04
1.81
2.41
7.40
6.60
5.80
7.70
8.00
5.32
5.92
5.25
4.66
2.22
1.97
1.75
7.10
6.30
5.60
7.60

32. 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.