Oxygen Affinity of the Transition MetalComplexes Of Schiff Base Ligands

لليجاندات اإلنتقالية العناصر شيفقواعد متراكباتلألكسجين الحاملة

Adel A.A. Emara

Associate Prof. in Inorganic ChemistryUniversity Collage in Mekkah

Umm Al-Qura University

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.

Outlines

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.

2-Natural Biological Oxygen Carrier Metal complexes

Location Source Metal Protein

CorpusclesCorpusclesCorpuscles

MammalsBirdsFishInsects

Fe (heme) Hemoglobin (Hb)

MuscleMuscleMuscle

MammalsOther vertebratesSome invertebrates

Fe (heme) Myoglobin (Mb)

PlasmaPlasmaPlasma

SnailsLugwormEarthworm

Fe (heme) Erythrocruorin (Ery)

Plasma Marine worms Fe (heme) Chlorocruorin (Chl)

Corpuscles Marine worms Fe (non-heme) Hemerythrin (Her)

PlasmaPlasma

MollusksArthropodes

Cu Hemocyanin (Hcy)

Corpuscles Ascidians V Hemovanadin (Hv)

R = -CH=CH2 : Protoporphyrin IX

R = CHO : Chlorocruoroporphyrin

N

N

N

NH

H

1 2

3

4

56

7

8

Figure 1. Structures of natural and synthetic porphyrins.

The numbers: methyl; vinyl; Propionic acid; ethyl or Phenyl substituents.

α, β, γ and δ position have the same substituent .

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.

(a) Schiff Base Ligands

C O

R1

R2

+ H2N R3 C

R1

R2

N R3

The condensation reaction between aldehydes or ketenes with primary amines.

4 -Synthesis of Schiff base ligands and their transition metal complexes

CO

OH

H

CO

OH

CH3 H3C

C

HC

O

C

H3C

OH

Salicyldehyde 2-Hydroxyacetophenone Acetylacetone

NH2 NH2 NH2 NH

NH2

Ethylenediamine (en) Diethylenetriamine (det)

Aldehydes and ketones

Amines

N N N N CCCC

RH3C CH3R

CC

H3C CH3

(C) Acacen

OH HO

(A) H2Salen and (B) H2-o-Hacen

OH OH

Figure 2. Representative structures of Schiff base ligands

C N

R1

R2

NH

N C

R1

R2

Ligand R1 R2

๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘ ๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘ ๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘๘

(D) H2Saldet H o-OHC6H4-

(E) H2o-Hacdet CH3 o-OHC6H4-

(F) H2Acacdet CH3 -CH=C(OH)CH3

Tetradentate Ligands

Pentadentate Ligands

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

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

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

Figure 3. Glove bag flushed with dry nitrogen gas used for handling the

starting materials and equipments.

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.

Figure 5. Reaction vessels used in synthesis of square planar and

square pyramide Schiff base metal(II) complexes.

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).

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. FormulaLigands 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(6.13)

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)

>300 74 Dark green

464.11 C20H31N3O6Mn [Mn(o-Hacdet)]

*. Oily product and the elemental analysis was not performed.

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 1384 vs 1240 m 1610 m 2866 m, br 3040 w, br [Ni(H2o-Hacdet)(NO3)2(H2O)]

305 vw 433 w 1384 vs 1199 m 1624 vs 2938 m, br 3052 m, br [Ni(Saldet)]

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.

t2g

eg

high spintetrahedral

high spinoctahedral

low spinoctahedral

low spin square pyramid

low spin square planar

t2g

eg

dx2-y2

dz2

dxy

dxz

dyz

dx2-y2

dz2

dxy

dxz

dyz

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.

TGA analysis

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

RN

NR

O O

M

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

RN N

HN

Co

R

OO

Structure 4. Square pyramide of the [Co(saldet)]

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

RN N

HN

M

R

HO OH

ONO2O2NO

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

In (a) suitable solvent and

(b) controlled temperature.

6- The Oxygen Sorption Process of the Metal Complexes of the Schiff Base Ligands

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)]

0.10 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.

Solubility in DMF and chloroform

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.

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 .

×)10-2 M (

Carrier

8.02 8.347.499.177.09

3.132.813.442.66

10.009.0011.008.5

1234

None 11.00 ]Co(o-Hacen) [

8.02 8.447.599.227.11

3.132.813.442.66

10.009.0011.008.5

1234

Pyridine 11.00

11.00 ]Co(o-Hacen) [

9.46 10.0011.177.499.17

3.754.192.813.44

12.0013.009.6011.00

1234

None 13.00 ]Co(Acacen) [

9.43 9.1811.217.259.17

3.754.192.813.44

12.0013.409.6011.00

1234

Pyridine 13.00

13.00 ]Co(Acacen) [

9.23 8.1811.117.499.42

3.444.192.723.53

11.0013.408.7011.30

1234

None 12.00 ]Co(Salen) [

9.26 9.1911.217.319.44

3.434.062.723.53

11.0013.408.7011.30

1234

Pyridine 12.00

12.00 ]Co(Salen) [

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 12.5012.0810.589.17

4.694.533.973.44

15.0014.5012.7011.00

1234

DMF 15.00 [Co(Saldet)]

6.00 6.426.665.335.57

2.412.502.002.09

7.708.006.406.70

1234

Chloroform 10.0 [Co(Saldet)]

3.75 4.434.003.573.01

1.661.501.341.13

5.304.804.303.60

1234

DMF 11.0 [Ni(Saldet)]

3.21 3.412.833.013.57

1.281.061.131.34

4.103.403.604.30

1234

Chloroform 10.0 [Ni(Saldet)]

4.11 4.434.004.593.49

1.661.501.721.31

5.304.805.504.20

1234

DMF 9.00 [Mn(o-Hacdet)]

3.60 4.163.493.173.57

1.561.311.191.34

5.004.203.804.30

1234

Chloroform 8.00 [Mn(o-Hacdet)]

Carrier loading %

[(Carrier complex)] + O2 carried [(Carrier complex)O2]

Mole of O2 carried

Carrier loading % = x 100 Mole of [(Carrier complex)O2]

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 .

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 6.587.147.256.50

2.472.682.722.44

7.908.608.707.80

1234

9.00 [Co(Saldet)]

6.25 5.686.006.746.58

2.132.252.532.47

6.807.208.107.90

1234

8.60 [Co(Saldet)]

5.71 6.165.444.826.42

2.312.041.812.41

7.406.605.807.70

1234

8.00 [Co(Saldet)]

5.32 5.925.254.665.44

2.221.971.752.04

7.106.305.606.60

1234

7.60 [Co(Saldet)]

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.

• 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:

1. Co(II) Schiff base complexes behave as good oxygen carriers than Ni(II) and Mn(II) Schiff base complexes.

2. Co(II) pentadentate Schiff base complexes is more effective as oxygen carriers than the Co(II) tetradentate Schiff base complexes.

3. 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.