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R.N. Firmo et al. / Polyhedron 117 (2016) 604–611
ꢀHOMO
þ
ꢀLUMO
IþA
(25 mmol) was added dropwise. After 24 h at room temperature,
the reaction solution was washed with a saturated solution of
NaHCO3 and the organic layers dried with MgSO4. After removing
the solvent under vacuum, 6.4 g of H2L were obtained, as viscous
yellow oil (96% yield). 1H NMR (CDCl3), ppm: 2.24 (s, 6H); 2.83
(s, 4H); 3.72 (s, 4H); 3.80 (s, 4H); 7.17 (dd, 4H, J = 4.9 Hz); 7.30
(s, 2H); 7.36 (d, 2H); 7.61 (dt, 2H, J = 7.7 Hz); 8,51 (ddd, 2H,
J = 4.9 Hz); 10.15 (s, 2H).
hardness, which can be calculated as
v
¼
¼ ꢁ
and
2
2
g
¼ I ꢁ A ¼ ꢀLUMO
ꢁ
ꢀHOMO [27]. The ionization potential (I) is
defined as I ¼ ꢁꢀHOMO and the electron affinity (A) is A ¼ ꢁꢀLUMO
.
2.4. Syntheses
2.4.1. 2-Hydroxy-5-methyl-benzaldehyde (HMB)
HMB was prepared by the Reimer-Tiemann reaction, by modifi-
cations of a previously described procedure [28]. In a 5 L three neck
round bottom flask, 42 mL of p-cresol (0.4 mol) dissolved in 2.0 L of
chloroform was heated in a water bath to 56–60 °C. Under vigorous
stirring, 120 g of sodium hydroxide (3.0 mol) dissolved in 100 mL
of distilled water was added, in small portions, during a 3 h period.
After another 1 h, the water bath was removed and the reaction
was left to cool down up to room temperature. Then, 500 mL of
cold water was added, followed by enough 6 mol/L HCl (in small
portions) to acidify the reaction solution (pH < 5). The organic layer
was removed, washed several times with distilled water and dried
under MgSO4. After removing the solvent, the remaining viscous
dark oil was distilled under low pressure (55–65 °C at 0.1 mmHg).
The product was obtained as a pale yellow solid, yielding 25 g of
HMB (46 % yield). 1H NMR (CDCl3), ppm: 2.34 (s, 3H), 6.90 (d,
1H), 7.34 (dd, 2H), 9.85 (s, 1H), 10.84 (s, 1H).
2.4.5. N,N0-bis(2-hydroxy-5-methyl-3-(hydroxyiminomethyl)benzyl)-
N,N0-bis-(pyridin-2-ylmethyl)ethylene diamine, H4Lox
In a 250 mL round bottom flask, 3.1 (5.75 mmol) of H2L were dis-
solved in 50 mL of anhydrous ethanol. Then, 1.6 g of NH2OH.HCl
(24 mmol) and 1.2 g of anhydrous Na2CO3 (12 mmol) were added
under magnetic stirring at room temperature. After 30 h, 150 mL
of distilled water was added and the product was extracted with
dichloromethane (6 ꢂ 50 mL). The organic layers were combined
and dried under MgSO4. After removing the solvent and keeping
the residual oil under vacuum for a few hours, 3.0 g of H4Lox were
obtained as a light green waxy solid (yield: 91 %). 1H NMR (CDCl3),
ppm: 2.17 (s, 6H); 2.76 (s, 4H); 3.63–3.75 (m, 8H); 6.93 (d, 2H); 7.07
(d, 2H); 7.14 (dd, 2H, J = 5.0 Hz); 7,37 (d, 2H, J = 7.7 Hz) 7.60 (dt, 2H,
J = 7.7 Hz); 8.29 (s, 2H); 8.46 (dd, 2H, J = 5.0 Hz).
2.4.6. [Fe(L)]NO3ꢀCH3OHꢀ2H2O (1)
2.4.2. 2-Hydroxy-3-(chloromethyl)-5-methyl-benzaldehyde (HCMB)
HCMB was prepared by a direct chloromethylation of HMB [29].
In a 250 mL round bottom flask, a mixture of 6.4 g (4.7 mmol) of
HMB, 7.5 mL of formaldehyde and 25 mL of HCl (12 mol/L) was
heated under magnetic stirring to reflux for 15 min. After cool
down the reaction to 0 °C, a solid mass was formed in the bottom.
The solid was separated from the reaction solution and recrystal-
lized in hot ethanol, yielding 5 g of HCMB (70% yield). The residual
solutions were basified with NaOH (pH > 9) prior to discard them.
1H NMR (CDCl3), ppm: 2.35 (s, 3H), 4.67 (s, 2H), 7.35 (2 s, 2H), 9.86
(s, 1H), 11.25 (s, 1H).
Special caution is required in this reaction due to the generation
of bis(chloromethyl)ether (BCME), a potent carcinogenic agent
[30]. The reaction was carried out in a fume hood, and all materials
and glassware washed with a 5% solution of NaOH in ethanol/
water 2:1.
In a 100 mL round bottom flask, 5 mL of a methanol solution
containing 0.21 g of Fe(NO3)3ꢀxH2O (0.5 mmol) was added to
0.27 g of H2L (0.5 mmol) previously dissolved in ethanol. A deep
blue solution was formed immediately, followed by precipitation
of a dark solid. 0.14 g of NaOAcꢀ3H2O (1 mmol) was added and
the suspension was stirred at room temperature for 2 h. The solid
was then removed by filtration and dissolved in methanol for crys-
tallization, affording 0.23 g of a dark blue microcrystalline solid of
[Fe(L)]NO3ꢀCH3OHꢀ2H2O (72 % yield). Anal. Calc. for [C33H40FeN5-
O
10]: C, 54.86; H, 5.58; N, 9.69. Found: C, 54.34; H, 5.55; N,
9.67%. ESI-MS (m/z+): 592.2, 100 % for [C32H32FeN4O4]+.
2.4.7. [Fe(H2Lox)]NO3ꢀ2H2O (2a)
In a 100 mL round bottom flask, 5 mL of a methanol solution
containing 0.20 g of Fe(NO3)3ꢀxH2O (0.5 mmol) was added to
0.28 g of H2Lox (0.5 mmol) previously dissolved in 10 mL of etha-
nol. A deep blue solution was formed immediately, without change
after addition of 0.14 g o NaOAcꢀ3H2O (1 mmol). After stirring for
3 h at room temperature, the solution was left to stand undis-
turbed. A dark blue crystalline solid was isolated after 10 days
(yield: 66 %). Anal. Calc. for [C32H38FeN7O9]: C, 53.34; H, 5.32; N,
13.61. Found: C, 53.20; H, 5.32; N, 13.43%. ESI-MS (m/z+): 622.3,
100 % for [C32H34FeN6O4]+.
2.4.3. N,N0-bis(pyridin-2-ylmethyl)ethylenediamine (py2en)
Py2en was prepared by
a condensation reaction between
2-pyridinecarboxaldehyde and ethylenediamine, followed by
reduction with NaBH4 [31]. In a 100 mL round bottom flask,
3.0 mL of pyridine-2-carboxaldehyde (31 mmol) were dissolved
in 30 mL of methanol at 0 oC, followed by the addition of 1.0 mL
of ethylenediamine (15,5 mmol), under magnetic stirring. After
1 h, 1.2 g of sodium borohydride (31 mmol) was added in small
portions and left to react for another 1 h. Then, HCl 6 mol/L was
added dropwise up to pH < 2. After removing the solvent, 30 mL
of distilled water was added and the pH adjusted to 9–10 with
NaOH. The product was extracted with dichloromethane
(6 ꢂ 50 mL); the organic layers were dried under MgSO4 and the
solvent was removed under vacuum, yielding 2.8 g of a yellow oil
of py2en (85 % yield). 1H NMR (CDCl3), ppm: 2.84 (s, 4H); 3.93
(s, 4H); 7.15 (dd, 2H, J = 4.9 Hz); 7.31 (d, 2H, J = 7.7 Hz); 7.63 (dt,
2H, J = 7.7 Hz); 8,54 (ddd, 2H, J = 4.9 Hz).
2.4.8. [Fe(H2Lox)]NO3ꢀ5H2O (2b)
In
a
100 mL round bottom flask, 0.070 g of NH2OHꢀHCl
(1.0 mmol) was added to a methanol solution of 1 (0.25 mmol)
and kept under magnetic stirring for 1 h. Then, 0.080 g of sodium
nitrate was added and the solution was left undisturbed for slow
evaporation of the solvent. After 20 days, a crystalline precipitate
was removed, giving 0.14 g of [Fe(H2LOX)]NO3ꢀ5H2O (yield: 70 %).
Anal. Calc. for [C32H44FeN7O12]: C, 49.62; H, 5.73; N, 12.66. Found:
C, 49.54; H, 5.72; N, 11.65%. ESI-MS (m/z+): 622.1, 100% for
[C32H34FeN6O4]+.
2.4.4. N,N0-bis(2-hydroxy-5-methyl-3-formylbenzyl)-N,N0-bis-
(pyridin-2-ylmethyl)ethylenediamine, H2L
3. Results and discussion
The ligand H2L was prepared by modifications of previously
described methods [32]. In a 100 mL round bottom flask, 4.6 g of
HCMB (25 mmol) and 3.0 g of py2en (12 mmol) were dissolved in
40 mL of dichloromethane. Then, 3.5 mL of triethylamine
3.1. Syntheses
The ligand H2Lox was synthesized by a simple condensation
reaction between H2L and hydroxylamine, to give the product in