Mono- and binuclear complexes of iron(III) with 1,2-Bis(2-hydroxybenzamido)ethane

Article abstract of DOI:10.1007/pl00013486

Complexes of the type [(Fe(L))₂O] · H₂O (H₂L=1,2-bis(2-hydroxybenzamido)ethane), [(Fe(L))₂ter] · 5H₂O H₂ter=terephthalic acid), [Fe(L)bpy]BPh₄ (bpy=2,2′-bipyridyl), and [Fe(L)phe

Full text of DOI:10.1007/pl00013486

Monatshefte fuÈr Chemie 129, 769±776 (1998)
Mono- and Binuclear Complexes of Iron(III)
with 1,2-Bis(2-hydroxybenzamido)ethane
Ã
ꢀ
Zdenek Smekal , Zdenek Sindelar, and Roman Klicka
Ï
Â
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Âꢀ
ꢀ
ꢁ
Department of Inorganic and Physical Chemistry, Palacky University, CZ-77147 Olomouc, Czech
Republic
Summary. Complexes of the type [(Fe(L))2O] Á H2O (H2L ˆ 1,2-bis(2-hydroxybenzamido)ethane),
[(Fe(L))2ter] Á 5H2O H2ter ˆ terephthalic acid), [Fe(L)bpy]BPh4 (bpy ˆ 2,20-bipyridyl), and
[Fe(L)phen]ClO4 Á H2O (phen ˆ o-phenanthroline) were prepared and studied by elemental analysis,
magnetochemical measurements, and spectroscopic methods. [(Fe(L))2O] Á H2O and [(Fe(L))2ter] Á
5H2O are probably binuclear, and the weak antiferromagnetic exchange interaction, (ꢀeff per one
atom of iron(III) was found to be 3.59 BM/77 Kꢀ4.91 BM/290 K (J ˆ ꢀ7 cmꢀ1, H ˆ ꢀ2JS1S2,
S1 ˆ S2 ˆ 5/2) for the ꢀ-oxo complex and 4.21 BM/82 Kꢀ5.35 BM/297 K (J ˆ ꢀ5 cmꢀ1) for the ꢀ-
terephthalato complex. The iron(III) complexes with bpy or phen are probably mononuclear; their
anomalous ꢀeff values (3.51 BM/80 Kꢀ3.68 BM/297 K for (Fe(L)bpy]BPh4 and 4.93 BM/259 K for
[Fe(L)phen]ClO4 Á H2O, respectively) agree neither with high spin (5.7±6.1 BM) nor with low spin
(2.1±2.5 BM) con®gurations.
Keywords. Iron(III) complexes; Magnetic properties, Antiferromagnetism; 1,2-Bis(2-hydroxybenz-
amido)ethane.
Mono- und binukleare Eisen(II)-Komplexe mit 1,2-Bis(2-hydroxybenzamido)ethan
Zusammenfassung. Komplexe des Typs [(Fe(L))2O] Á H2O (H2L ˆ 1,2-Bis(2-hydroxybenzamido)-
ethan), [(Fe(L))2ter] Á 5H2O (H2ter ˆ Terephthalsaure), [Fe(L)bpy]BPh4 (bpy ˆ 2,20-Bipyridyl) und
È
[Fe(L)phen]ClO4 Á H2O (phen ˆ o-Phenanthrolin) wurden hergestellt und mittels Elementaranalyse,
magnetochemischer Messungen und spektroskopischer Methoden untersucht. [(Fe(L))2O] Á H2O und
[(Fe(L))2ter] Á 5H2O sind wahrscheinlich binuklear, und die schwache antiferromagnetische
Austauschwechselwirkung (ꢀeff pro Eisen(III)-Atom) wurde fuÈr den ꢀ-oxo-Komplex zu 3.59 BM/
77 Kꢀ4.91 BM/290 K (J ˆ ꢀ7 cmꢀ1, H ˆ ꢀ2JS1S2, S1 ˆ S2 ˆ 5/2) und fuÈr den ꢀ-terephthalato-
Komplex zu 4.21 BM/82 Kꢀ5.35 BM/297 K (J ˆ ꢀ5 cmꢀ1) ermittelt. Die Eisen(III)-Komplexe mit
bpy bzw. phen sind wahrscheinlich mononuklear; ihre anomalen ꢀeff-Werte (3.41 BM/
80 Kꢀ3.68 BM/297 K fuÈr [Fe(L)bpy]BPh4 und 4.93 BM/259 K fuÈr [Fe(L)phen]ClO4 Á H2O sind
È
weder mit high-spin- (5.7±6.1 BM) noch mit low-spin-Zustanden (2.1±2.5 BM) in Einklang zu
bringen.
Introduction
The aim of this work was the preparation and physicochemical investigation of
new complexes of iron(III) with tetradentate amides derived from salicylic acid and
Ã
Corresponding author

Â
Z. Smekal et al.
770
Fig. 1. 1,2-Bis(2-hydroxybenzamido)ethane (H2L)
ethylenediamine in a molar ratio of 2:1 (H2L ˆ 1,2-bis(2-hydroxybenzamido)-
ethane) (Fig. 1) and their comparison with complexes of iron(III) with analogous
Schiff bases (H2salen (N,N0-bis(salicylidene)ethylenediamine), H2salpn (N,N0-
bis(salicylidene)propylenediamine), and H2saloph (N,N0-bis(salicylidene)-o-phe-
nylenediamine)). We found only few articles in the literature about complexes with
1,2-bis(2-hydroxybenzamido)ethane (H4L). Liao et al. [1±5] have synthesized the
copper(II) complex Na2[Cu(L)] Á 5H2O and binuclear complexes with exchange
interaction between the central atoms of the compositions [Cu(L)Mn(L0)2],
[Cu(L)Fe(L0)Cl], [Cu(L)Cu(L0)], and [Cu(L)Ni(L0)2] (L0 ˆ 2,20-bipyridine (bpy) or
o-phenanthroline (phen)). The copper(II) atom is four-coordinated (by two
deprotonated phenolic oxygens and two deprotonated nitrogens from amide
groups) in the square-planar arrangement. The oxygen atoms from the phenolic
groups form bridges in the above mentioned binuclear compounds, and the ligand
1,2-bis(2-hydroxybenzamido)ethane appears as dianion (L2ꢀ) against tetraanion
(L4ꢀ) in Liao's complexes. The mononuclear complexes [Fe(L)bpy]BPh4 (1) and
[Fe(L)phen]ClO4 Á H2O (2) were prepared by reaction of H2L, FeCl3 Á 6H2O, Et3N,
MeONa, and bpy with NaBPh4 or phen Á H2O with LiClO4 Á 3H2O. The ꢀ-oxo
complex [(Fe(L))2O] Á H2O (3) was obtained by reaction of H2L, FeCl3 Á 6H2O, and
aqueous NH3 in methanol, and the ꢀ-terephthalato complex [(Fe(L))2ter] Á 5H2O
(4) from the ꢀ-oxo complex and terephthalic acid (H2ter). The compounds were
characterized by elemental analysis, IR and UV/Vis spectroscopy and variable
temperature magnetic susceptibility measurements (77±297 K).
Results and Discussion
The chemical compositions of the substances prepared are given in Table 1, the
data from physico-chemical studies in Tables 2±6 and Figs. 2±4.
The IR spectra were not studied in detail; only the characteristic vibration
ꢁ(C=O) was interpreted [6] (Table 2). It appears at 1640 cmꢀ1 in free H2L; in the
Table 1. Chemical compositions of the complexes
Found (Calcd.) (%)
C
H
N
Cl
Fe
[(Fe(L))2O] Á H2O
[(Fe(L))2ter] Á 5H2O
[Fe(L)bpy)BPh4
51.8 (51.8)
49.5 (49.9)
72.2 (72.4)
51.8 (51.6)
4.4 (4.1)
4.7 (4.4)
5.0 (5.1)
3.8 (3.7)
7.2 (7.6)
6.1 (5.8)
7.2 (6.8)
8.6 (8.6)
±
14.5 (15.1)
±
12.3 (11.6)
±
±
±
[Fe(L)phen]ClO4 Á H2O
4.9 (5.4)

Iron(III) Complexes with 1,2-Bis(2-hydroxybenzamido)ethane
771
Table 2. Magnetic and IR spectroscopic properties of the complexes
ꢀeff (BM)/T (K)a
IR (cmꢀ1
†
ꢁ(C=O)
[(Fe(L))2O] Á H2O
[(Fe(L))2ter] Á 5H2O
[Fe(L)bpy)]BPh4
3.59/77±4.91/290
4.21/82±5.35/297
3.51/80±3.68/297
4.93/295
1604 m
1604 m
1604 m
1600 m
[Fe(L)phen]ClO4 Á H2O
a Per atom of iron(III)
Table 3. UV/Vis spectroscopic properties of the complexes
Colour
UV/Vis (nm)a
[(Fe(L))2O] Á H2O
[(Fe(L))2ter] Á 5H2O
[Fe(L)bpy)]BPh4
red
516, 633 sh
506, 560 sh
red
red
440, 705 sh, 740
570
[Fe(L)phen]ClO4 Á H2O
a Diffuse-re¯ectance spectra
brown
Table 4. Magnetic properties of [(Fe(L))2O] Á H2O
a
T (K)
ꢂM (cm3 Á molꢀ1
†
ꢀeff (BM)
290.3
261.4
224.6
166.1
123.5
110.6
86.0
0.0207
0.0227
0.0256
0.0317
0.0373
0.0390
0.0411
0.0419
6.94
6.89
6.78
6.49
6.07
5.87
5.32
5.07
76.6
a Molar susceptibility per molecule corrected for diamagnetism
complexes, ꢁ(C=O) is shifted to about 1600±1604 cmꢀ1, indicating the coordina-
tion of the ligand to the iron(III).
There is no information about the electronic structure of iron(III) from diffuse-
re¯ectance UV/Vis spectra (Table 3). Only charge-transfer bands were observed
which are in accordance with data for iron(III) complexes with organic ligands [7].
The electronic spectra of solutions of the compounds in dimethylformamide are
dissimilar to the diffuse-re¯ectance spectra. The complexes are instable in
dimethylformamide solutions.
A magnetochemical study of [(Fe(L))2O] Á H2O (3) and [(Fe(L))2ter] Á 5H2O (4)
was performed in the range of 77±297 K (Tables 4 and 5, Figs. 2 and 3). The
magnetic moments per atom of iron(III) decrease with decreasing temperature from
4.91 BM at 290 K to 3.59 BM at 77 K for [(Fe(L))2O] Á H2O and from 5.35 BM at

Â
Z. Smekal et al.
772
Table 5. Magnetic properties of [(Fe(L))2ter] Á 5H2O
T (K)
ꢂM (cm3 Á molꢀ1
†
ꢀeff (BM)
296.8
270.1
220.3
186.4
158.2
135.1
118.5
106.3
91.1
0.0241
0.0263
0.0307
0.0350
0.0395
0.0437
0.0471
0.0497
0.0519
0.0541
7.56
7.54
7.35
7.22
7.07
6.87
6.68
6.50
6.15
5.95
81.7
a Molar susceptibility per molecule corrected for diamagnetism
Table 6. Magnetic properties of [Fe(L)bpy]BPh4
T (K)
ꢂM (cm3 Á molꢀ1
†
ꢀeff (BM)
296.8
265.1
235.4
180.6
148.1
125.7
98.3
0.00571
0.00654
0.00725
0.00925
0.0112
0.0131
0.0163
0.0192
3.68
3.72
3.69
3.66
3.65
3.63
3.58
3.51
80.2
a Molar susceptibility corrected for diamagnetism
Fig. 2. Paramagnetic susceptibility ꢂM (*, cm3 Á molꢀ1) and effective magnetic moment ꢀeff (*,
BM) vs. temperature for [(Fe(L))2O] Á H2O (3); circles: experimental, solid lines: calculated
according to Eq. (1)

Iron(III) Complexes with 1,2-Bis(2-hydroxybenzamido)ethane
773
Fig. 3. Paramagnetic susceptibility ꢂM (*, cm3 Á molꢀ1) and effective magnetic moment ꢀeff (*,
BM) vs. temperature for [(Fe(L))2ter] Á 5H2O (4); circles: experimental, solid lines: calculated
according to Eq. (1)
Fig. 4. Paramagnetic susceptibility ꢂM (*, cm3 Á molꢀ1) and effective magnetic moment ꢀeff (*,
BM) vs. temperature for [(Fe(L)bpy]BPh4 (1); circles: experimental, solid lines: calculated according
to Curie-Weiss' law
297 K to 4.21 BM at 82 K for [(Fe(L))2ter] Á 5H2O. The complexes behaves like
iron(III) binuclear compounds (H ˆ ꢀ2JS1S2, S1 ˆ S2 ˆ 5/2). An expression for the
molar paramagnetic susceptibility for an S1 ˆ S2 ˆ 5/2 exchange-coupled binuclear
compound has been presented [8] (Eq. 1):
ꢀ
ꢁ
Ng2ꢃ2 2A ‡ 10B ‡ 28C ‡ 60D ‡ 110E
ꢂM ˆ
‡ Nꢄ
ꢁ1†
kT
1 ‡ 3A ‡ 5B ‡ 7C ‡ 9D ‡ 11E
The exponentional terms are: A ˆ exp(2J/kT ), B ˆ exp(6J/kT), C ˆ exp(12J/kT ),
D ˆ exp(20J/kT), and E ˆ exp(30J/kT); Nꢄ, g, ꢃ, k and T have their usual meaning
(ꢂM is the molar susceptibility per molecule corrected for diamagnetism). A least-
square ®tting program [9] was used to ®t the data for the Fe(III) complexes to the

Â
Z. Smekal et al.
774
above mentioned equation. The best parameters are J ˆ ꢀ7 cmꢀ1, g ˆ 2.0, and
Nꢄ ˆ 0 for the ꢀ-oxo complex and J ˆ ꢀ5 cmꢀ1, g ˆ 2.0 and Nꢄ ˆ 0 for the ꢀ-
terephthalato complex. A comparison of the values of the exchange integrals J of
compounds 3 and 4 with those of compounds with analogous Schiff bases (H2salen,
H2salpn, and H2saloph) reveal that [(Fe(L))2O] Á H2O is weakly antiferromagnetic
against [(Fe(salen))2O] (J ˆ ꢀ95 cmꢀ1), [(Fe(salpn))2O] (J ˆ ꢀ90 cmꢀ1) and
[(Fe(saloph))2O] (J ˆ ꢀ95 cmꢀ1) [10]. [(Fe(samen))2ter] Á 5H2O as well as
[(Fe(saloph))2ter] show weak antiferromagnetism (J ˆ ca. ꢀ5 cmꢀ1); no exchange
interaction was found for [(Fe(salen))2ter] [11].
The compounds [Fe(L)bpy]BPh4 (1) and [Fe(L)phen]ClO4 Á H2O (2) described
in this paper are probably mononuclear octahedral complexes, but their unusual
magnetic moments are neither in agreement with high-spin (5.7±6.1 BM) nor low-
spin (2.1±2.5 BM) con®guration [12]. Regarding their anomalous ꢀeff values
(3.68 BM (1) or 4.93 BM (2) at room temperature), the temperature dependence of
the magnetic susceptibility of [Fe(L)bpy]BPh4 was measured. It obeyes the Curie-
Weiss law (C ˆ 2.0 cm3 Á molꢀ1 Á Kꢀ1, ꢅ ˆ ꢀ19 K). Upon lowering the temperature,
the magnetic moment decreases (3.68 BM/297 Kꢀ3.51 BM/80 K) (Table 6, Fig. 4).
The magnetic properties of 1 and 2 can be compared with those of complexes with
analogous Schiff bases (H2salen and H2saloph). Recently [11, 13, 14], octahedral
complexes of the types [Fe(salen)L]BPh4 (L ˆ bpy or phen) and [Fe(saloph)L]ClO4
(L ˆ bpy or phen) have been characterized. It has been found that the compounds
with salen have high-spin (S ˆ 5/2) and those with saloph have low-spin (S ˆ 1/2)
con®guration. Saloph has a stronger ligand ®eld than salen. The origin of the
anomalous magnetic moments of compounds 1 and 2 is unknown.
The newly prepared compounds [(Fe(L))2O] Á H2O and [(Fe(L))2ter] Á 5H2O are
probably binuclear complexes in which each iron(III) atom is coordinated by the
tetradentate amide and by an oxygen bridge (Fig. 5) or by two oxygens from
terephthalato bridge. The complexes [Fe(L)bpy]BPh4 and [Fe(L)phen]ClO4 Á H2O
are probably mononuclear octahedral complexes (donors atoms are two nitrogens
from bpy or phen, two oxygens from phenolic groups, and two nitrogens from
amide groups).
Fig. 5. Proposed structure of [(Fe(L))2O] Á H2O (3)

Iron(III) Complexes with 1,2-Bis(2-hydroxybenzamido)ethane
775
Experimental
Materials and Methods
Methyl salicylate (p.a.): Riedel-de Haen AG, Seelze-Hannover; ethylenediamine (p.a) and
triethylamine (p.): Downs Development Chemicals Limited; FeCl3 Á 6H2O (p.a.): Winlab Limited,
Maindenhead, Berkshire, UK; sodium terephthalate (p.a.): VEB Laborchemie Apolda. All chemicals
were used without further puri®cation. LiClO4 Á 3H2O was prepared by reaction of HClO4 (Carlo
Erba) and LiOH Á H2O (Lachema Brno).
Elemental analyses (carbon, hydrogen, and nitrogen) were performed on a Fisons Instruments EA
1108 CHN analyzer. The Fe content was determined thermogravimetrically as Fe2O3 after thermal
decomposition of the samples. The content of chlorine was estimated by the Schoniger method.
Electron diffuse-re¯ectance or absorption spectra were run on a Specord M40 in Nujol or in
dimethylformamide solutions. IR spectra were recorded on a Specord IR 80 instrument in Nujol
mulls. The magnetic susceptibility was measured using the Faraday method on a magnetic balance
constructed in our laboratory. The temperature dependence of magnetic susceptibilities was
measured in the range of 77±297 K. Hg[Co(SCN)4] was used as a calibrant, and diamagnetic
corrections were made with Pascal's constants for all constituent atoms.
Syntheses
1,2-Bis(2-hydroxybenzamido)ethane (H2L)
63.2 ml (0.49 mmol) of methyl salicylate were added to 16.3 ml (0.24 mmol) of ethylenediamine.
The reaction mixture was re¯uxed for 5 hours. After cooling a solid was obtained. The amide
was recrystallized three times from hot methanol. The white product was ®ltered off, washed with
a small amount of cold methanol, and dried under an infralamp at 40ꢂC. The yield was 20 g
(27%). The substance is well soluble in hot ethanol and hot methanol and insoluble in water; m.p.:
183.5ꢂC.
[Fe(L)bpy]BPh4
A solution of 0.90 g (3.3 mmol) of FeCl3 Á 6H2O in 10 ml of ethanol was added to a solution of 1.00 g
(3.3 mmol) of H2L in 15 ml of warm ethanol. To the stirred reaction mixture, 0.20 ml (1.4 mmol) of
triethylamine were added dropwise. After short re¯ux (10 min), solutions of MeONa in methanol
(10 ml, c ˆ 0.22 mol Á dmꢀ3) and of 0.52 g (3.3 mmol) of bpy in 5 ml of ethanol were added. After
short re¯ux (15 min), 1.13 g (3.3 mmol) of NaBPh4 in 10 ml of ethanol was added to the well stirred
hot reaction mixture. The precipitate was ®ltered off, washed properly with water, ethanol, and
diethyl ether and dried at 40ꢂC. The yield was 0.5 g (20%). The product is insoluble in water,
methanol, and ethanol and soluble in dimethylformamide.
[Fe(L)phen]ClO4 Á H2O
This substance was obtained using the same method as described for the preparation of
[Fe(L)bpy]BPh4 (starting materials: 0.65 g (3.3 mmol) of phen Á H2O and 0.53 g (3.3 mmol) of
LiClO4 Á 3H2O; the product precipitated after concentration to one half of the volume and addition of
15 ml of diethyl ether with some delay). The yield was 0.25 g (10%). The product is insoluble in
water, partially soluble in methanol and ethanol, and soluble in dimethylformamide and
nitromethane.

Â
Z. Smekal et al.: Iron(III) Complexes with 1,2-Bis(2-hydroxybenzamido)ethane
776
[(Fe(L))2O] Á H2O
A solution of 1.80 g (6.6 mmol) of FeCl3 Á 6H2O in 20 ml of methanol was added to a solution of
2.00 g (6.6 mmol) of H2L in 20 ml of hot methanol. The colour turned to purple. Then, a solution of
NH3 in methanol (the solution was prepared by mixing of 10 ml of 26% aqueous NH3 and 50 ml of
methanol) was added dropwise to the well-stirred hot reaction mixture until it was alkaline. The
precipitate formed was ®ltered off, washed with ethanol and methanol, and dried at 40ꢂC. The yield
was 2.0 g (80%). The product is insoluble in water, methanol, ethanol and nitromethane, and soluble
in dimethylformamide and dimethylsulfoxide.
[Fe(L))2ter] Á 5H2O
A solution of 0.08 g (0.49 mmol) of terephthalic acid in 10 ml of nitromethane was added to a
suspension of 0.37 g (0.49 mmol) of [(Fe(L))2O] Á H2O in 15 ml of nitromethane. The well-stirred
reaction mixture was re¯uxed for 3 hours. After cooling the solid was ®ltered off, washed with
methanol and diethyl ether, and dried at 40ꢂC. The yield was 0.4 g (85%). The product is insoluble in
water, methanol, ethanol, and nitromethane and soluble in dimethylformamide.
Acknowledgements
Ï Â
The authors are indebted to E. Miskova for performing the elemental analyses. This work was
supported by the Czech Agency of the Czech Republic (Grant No. 203/96/0440).
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Received January 12, 1998. Accepted (revised) March 16, 1998