A new iron(III) complex of glycine derivative of amine-chloro substituted phenol ligand: Synthesis, characterization and catechol dioxygenase activity

Article abstract of DOI:10.1016/j.molstruc.2012.06.047

A new iron(III) complex of the glycine derivative of amine-chloro substituted phenol ligand (H₃L^GDC) has been prepared and characterized by IR, ¹H NMR, UV-Vis spectroscopic techniques, cyclic voltammetry, ESI-MS and magnet

Full text of DOI:10.1016/j.molstruc.2012.06.047

Journal of Molecular Structure 1029 (2012) 60–67
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
A new iron(III) complex of glycine derivative of amine-chloro substituted
phenol ligand: Synthesis, characterization and catechol dioxygenase activity
a
b
c
Iraj Saberikia a, Elham Safaei a, , Mohammad Hossein Kowsari , Yong-Ill Lee , Patricia Cotic ,
⇑
Giuseppe Bruno d, Hadi Amiri Rudbari d
a Institute for Advanced Studies in Basic Sciences (IASBS), 45137-66731 Zanjan, Iran
b Department of Chemistry, Changwon National University, Changwon 641-773, South Korea
c Institute of Mathematics, Physics and Mechanics, University of Ljubljana, Ljubljana, Slovenia
d Dipartimento di Chimica Inorganica, Salita Sperone 31, Università di Messina, 98166 Messina, Italy
h i g h l i g h t s
"
"
"
An iron(III) complex of glycine derivative of chloro-substituted bis(phenol)amine synthesized.
The complex displayed paramagnetic and metal-centered reduction, and a ligand-centered oxidation.
The oxygenation cleavage of catechol derivatives with this complex was investigated.
a r t i c l e i n f o
a b s t r a c t
A new iron(III) complex of the glycine derivative of amine-chloro substituted phenol ligand (H3LGDC) has
been prepared and characterized by IR, 1H NMR, UV–Vis spectroscopic techniques, cyclic voltammetry,
ESI-MS and magnetic susceptibility studies. X-ray analysis reveals that in iron complex of FeLGDC the
iron(III) center has a distorted trigonal bipyramidal coordination sphere and is surrounded by an amine
nitrogen, a carboxylate, a water and two phenolate oxygen atoms. The DFT calculations with the UB3LYP/
6-311++Gꢀꢀ level optimized structure of the complex are in good agreement with experimental X-ray
structural data. The variable-temperature magnetic susceptibility indicates that FeLGDC is the paramag-
netic high spin iron(III) complex. It has been shown that electrochemical oxidation of this complex is
ligand-centered due to the oxidation of phenolate to the phenoxyl radicals. This enzyme mimic utilized
molecular oxygen in carrying out the oxidative cleavage of catechols with complete conversion at room
temperature.
Article history:
Received 30 May 2012
Received in revised form 24 June 2012
Accepted 25 June 2012
Available online 4 July 2012
Keywords:
Amine bis(phenolate)
Non-heme iron
Model complex
Iron complex
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
catechol substrates are classified according to the different redox
states of the iron associated with different reaction mechanisms
Aromatic hydrocarbons are highly toxic environmental pollu-
tants that can be degraded by bacteria under aerobic conditions.
The aerobic biodegradation of these compounds is usually initiated
by dioxygenases, which catalyze the oxidative cleavage of these
compounds with concomitant insertion of both oxygen atoms of
molecular oxygen into the aromatic ring of the substrate resulting
in ring cleavage [1–3]. This large family of enzymes utilizes similar,
mononuclear non-heme iron centers to activate the oxygen mole-
cule to perform oxygenation at lateral positions and a variety of
important biological functions [4–8]. Non-heme–iron dependent
dioxygenase enzymes which catalyze the oxidative cleavage of
[9]. The intradiol catechol dioxygenases utilize mononuclear iro-
n(III) centers to catalyze the oxidative cleavage of the carbon–car-
bon bond between the two phenolic hydroxyl groups, while the
extradiol-type enzymes contain a non-heme iron(III) molecule,
cleave the adjacent carbon–carbon bond (Scheme 1).
Intradiol-type dioxygenases activate the metal-bound sub-
strate, whereas the extradiol-type dioxygenases activate the O2
bound to the iron, copper, manganese and magnesium containing
dioxygenases have also been isolated [10].
Several bioinorganic modeling studies [9–30] have focused on
the structural and spectroscopic characterization of iron(III) com-
plexes of tripodal tetradentate, tetraaza macrocyclic and tetraden-
tate bis(phenolate) ligands [12–14,19–31] as structural and
functional models for the catecholate–iron(III) form of catechol
dioxygenases. According to these studies, the significance of Lewis
⇑
Corresponding author. Tel.: +98 241 4153200; fax: +98 241 4153232.
E-mail address: safaei@iasbs.ac.ir (E. Safaei).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.06.047

I. Saberikia et al. / Journal of Molecular Structure 1029 (2012) 60–67
61
out under the optimized instrument conditions. All reported mass
spectra are the average of at least 30 consecutive scans.
The mass spectrometry was performed on a QToF Premier
(Waters, Manchester, UK) tandem mass spectrometer which had
a quadrupole time-of-flight detector with orthogonal acceleration
in V mode. The system was operated by MassLynx 4.1 software
(Waters-Micromass, Manchester, UK) in positive ion electrospray
mode. High purity nitrogen was used as the nebulizer and auxiliary
gas, and argon was the collision gas. The nebulizer gas was set to
150 L/h at 150 °C and the cone gas and the source temperatures
were set to 20 L/h and 90 °C, respectively. The capillary, extraction,
and sample cone voltages were set to 3.0 V, 5.0 V, and 25 V, respec-
tively. The instrument was operated in full-scan mode with QToF
data collected between m/z 100–1000, with collision energy of
3 eV. The data were stored in the centroid mode with a scan time
of 0.5 s and an inter scan delay of 0.01 s. The MS/MS experiments
were performed using collision energies which were optimized
for the corresponding analytes. Samples were injected at a flow
Scheme 1. Scheme of cleavage by intradiol and extradiol dioxygenases [7].
rate of 5 lL/min. The QToF detector (MCP) was operated at 2100 V.
GC–MS was performed with a Clarus 600 GCMS (Perkin Elmer,
Waltham, MA, USA). A 30 m capillary column coated with (5%
diphenyl)dimethylpolysiloxane (0.25 mm i.d. and 1 lm film thich-
ness; Elite-5MS, Perkin Elmer, Waltham, MA, USA) was used. The
carrier gas was He at a flow 1.0 mL/min. Injection port and transfer
line temperature was 270 °C. Samples were injected in methanol.
The oven temperature program started at 70 °C (5 min), was raised
at 20 °C/min to 200 °C, held for 15 min. and heated at 10 °C/min to
310 °C hold for 5.5 min. The quadrupole mass spectrometer was
operated in EI mode (70 eV), scanning between m/z 40 and 520.
The ion source temperature was 230 °C.
Magnetic susceptibility were measured from powder samples
of solid material in the temperature range 2–300 K by using a
SQUID susceptometer (Quantum Design MPMS-XL-5) in a mag-
netic field of 1000 Oe.
Scheme 2. Structure of [2-(bis(3,5-dichloro-2-hydroxybenzyl) amino) acetic acid]
(H3LGDC).
acidity of iron(III) centers in the dioxygenase reactions have been
highlighted [9–20].
In this paper, we report the synthesis, characterization, mag-
netic and redox properties, and catalytic activity of FeLGDC complex
of [NAO]-donor tripodal amine phenol ligand H3LGDC, 2-(bis-(3,5-
dichloro-2-hydroxybenzyl)amino)acetic acid) (Scheme 2) which
provide the coordination sphere around iron center. The oxygena-
tion of catechol family with FeLGDC as a functional model for cate-
chol dioxygenases will be investigated with emphasize on the role
of chlorine substituents on the catalytic activity of complex.
Voltammetric measurements were made with a computer con-
trolled Auto Lab electrochemical system (ECO Chemie, Ultrecht,
The Netherlands) equipped with a PGSTA 30 model and driven
by GPES (ECO Chemie). A glassy carbon electrode with a surface
area of 0.035 cm2 was used as a working electrode and a platinum
wire served as the counter electrode. The reference electrode was
an Ag wire as the quasi reference electrode. Ferrocene was added
as an internal standard after completion of a set of experiments,
and potentials are referenced vs. the ferrocenium/ferrocene couple
(Fc+/Fc).
2. Experimental
2.1. Materials and physical measurements
Diffraction data for FeLGDC was measured on a Bruker–Nonius
X8 ApexII diffractometer equipped with a CCD area detector by
Reagents or analytical grade materials were obtained from com-
mercial suppliers and used without further purification, except those
for electrochemical measurements. Elemental analyses (C, H, N)
were performed by were performed by the Elementar, Vario EL III.
Fourier transform infrared spectroscopy on KBr pellets was per-
formed on a FT IR Bruker Vector 22 instrument. NMR measurements
were performed on a Bruker 400 instrument. UV–Vis absorbance dig-
itized spectra were collected using a CARY 100 spectrophotometer.
The electronic spectra of the complex recorded in the CH2Cl2 solvent.
The ligand samples were dissolved in acetonitrile (1.0 ꢁ 10ꢂ4 M)
and mixed with deionized water (1:1) just before the mass spectro-
scopic measurements. The identification of interaction products
was performed using Thermo Finigan LCQ advantage ion trap mass
spectrometer equipped with electrospray ionization. For sample
injections, the instrument syringe pump was used at flow rate of
2 L/min. The instrumental operation conditions were as follows;
spray voltage, 4.58 kV; source current, 0.48 A; sheath gas flow
rate,19.43 L/min; capillary voltage; 9.44 V, capillary temperature
100 °C, tube lens voltage; 55 V. Experiments were performed in po-
sitive-ion mode and optimized by Xcalibur software before the
experiments. All MS experiments in this work have been carried
using graphite-monochromated Mo K
a radiation (k = 0.71073)
generated from a sealed tube source. Data were collected and re-
duced by smart and saint software [32] in the Bruker package.
The structure was solved by direct methods [33], than developed
by least squares refinement on F2 [34]. All non-H atoms were
placed in calculated positions and refined as isotropic with the
‘‘riding-model technique’’. Details concerning collection and analy-
sis are reported in Table 1.
2.2. Preparations
2.2.1. Synthesis of H3LGDC
The ligand was synthesized according to modified literature
procedure [35–39]. As aqueous formaldehyde was one of the re-
agents, in some cases no added solvent was required beyond what
was already present in the reagents solution.
A solution of 2,4-dichlorophenol (7.80 g, 48.00 mmol), 2-amino-
acetic acid (1.8 g, 24.00 mmol), and 37% aqueous formaldehyde
(3.58 mL, 48.00 mmol) was stirred and refluxed for 48 h. Upon
cooling, a large quantity of beige solid was formed. The solvent

62
I. Saberikia et al. / Journal of Molecular Structure 1029 (2012) 60–67
Table 1
3,5-DTBC, the products were extracted from the aqueous solution
Crystal data and structure refinement for Fe2(LTHF)3.
with diethyl ether (3 ꢁ 30 mL). The organic layer was separated,
washed with 2 M HCl (2 ꢁ 20 mL) and then dried over anhydrous
Na2SO4 at room temperature and then filtered off and the filtrate
was evaporated to give cleavage products in small amounts. The
major product was quantified by comparing the TLC retention fac-
tor (Rf) values and 1H NMR signals with the related values of the
same sample reported previously [40].
The same experiment was repeated in the absence of any catalyst,
no oxidation products were obtained. The complex (0.05 mmol),
H2DBC (0.222 g, 1.00 mmol), and Et3N (280 mL, 2.0 mmol) were dis-
solved in 5 mL of one of solvent (DMF, acetonitrile, ethanol or meth-
anol) and exposed to dioxygen and stirred for 48 h.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C32 H26 Cl8 Fe2 N4 O13
1069.87
296(2) K
0.71073 Å
Monoclinic
I2/a
a = 14.686(3) Å alpha = 90°
b = 8.8354(16) Å beta = 92.954(18)°
c = 33.720(8) Å gamma = 90°
4369.5(15) Å3
a (Å)
b (Å)
c (Å)
Volume (Å3)
Z
4
Calculated density (mg/m3)
Absorption coefficient (mmꢂ1
F(000)
1.626 mg/m3
)
1.21–25.00°
2152
Crystal size (mm)
Theta range for data collection
Limiting indices
Reflections collected/unique
Completeness
0.41 ꢁ 0.14 ꢁ 0.02 mm
1.21–25.00°
3. Results and discussion
ꢂ17 6 h617, ꢂ10 6 k 6 10, ꢂ40 6 l 6 40
57648/3860 [R(int) = 0.1785]
99.9%
This present ligand (2-(bis(3,5-dichloro-2-hydroxybenzyl) ami-
no) acetic acid) H3LGDC) was synthesized according to known pro-
cedure [35–39] which involve employing methanol free Mannich
condensation of the corresponding phenol, amine and formalde-
hyde. Since the formaldehyde used in the reaction contained 63%
water, the process was carried in water instead of methanol as re-
ported for similar aminophenol ligands. Iron complex FeLGDC was
easily formed in good yields by refluxing methanolic solution of
the ligand with iron(III) chloride hexa-aqua and triethylamine in
suitable ratio.
Extinction coefficient
Refinement method
0.031(8)
Full-matrix least-squares on F2
3860/3/259
Data/restraints/parameters
Goodness-of-fit on F2
2.906
Final R indices [I > 2sigma(I)]
R indices (all data)
R1 = 0.2589, wR2 = 0.6165
R1 = 0.2938, wR2 = 0.6476
2.698 and ꢂ1.263 e Aꢂ3
Largest diff. peak and hole (e Aꢂ3
)
was decanted, and the remaining solid residue was washed with
cold methanol to give a pure, white powder (6 g, 30% yield).
1H NMR (400 MHz, DMSO, 298 K): d 3.32 (s, 2H); 3.81 (s, 4H);
7.15 (d, 2H); 7.38 (d, 2H); 10.63 (br, 1HOH). 13C NMR (400 MHz,
DMSO, 298 K): d 173.25, 151.60, 128.82, 128.52, 127.38, 123.18,
121.64, 54.42, 54.23.
FeCl3;6H2
O
H2LGDC
FeLGDC
ð1Þ
ꢀꢀꢀꢀꢀ!
Ethanol;NEt3
The strong band at around 3420–3440 cmꢂ1, corresponding to OH
stretching mode of ligand, was replaced by a broad band in IR spec-
tra of complex. This observation proves the coordination of phenol
groups to the metal ion.
13C NMR (100.6 MHz, DMSO, 298 K): d 173.2, 151.6, 128.8,
128.5, 127.3, 123.1, 121.6, 54.4, 54.2. IR (cmꢂ1): 3428 (OH); 3083
(OH); 2956 (CAH); 1733 (C@O); 1635 (C@C, phenyl ring). m.p.
207 °C.
The electronic absorption spectra of FeLGDC exhibit two bands in
CH2Cl2 solution. The first band is apparent in 300–800 nm range (in
the near UV), and one more in the visible region with high absorp-
tion coefficient (ꢄ12800 Mꢂ1 cmꢂ1). The lower energy band
(460 nm) of FeLGDC is assigned to a charge-transfer transition from
2.2.2. Synthesis of FeLGDC
Triethylamine (0.40 mL, 3.00 mmol) was added to a solution of
H3LGDC (0.42 g, 1.00 mmol) in ethanol. FeCl3ꢃ6H2O (0.27 g,
1.00 mmol) was added to this solution and the resulting mixture
was stirred for 1 h, resulting in an intense purple solution. The
solvent was removed and the solid material recrystallized in 1:1
acetone/water mixture. Yield: 0.32 g (63%). Anal. calcd. for
the
p
orbital (HOMO) of the phenolate oxygen to the pꢀ orbital of
iron(III), and thus its band position falls in the range of other
phenolato compounds (Section 2.2.2). The higher energy band
(289 nm) is associated with the
p
orbital to pꢀ orbital of the pheno-
late ion charge transfer (ILCT) [41–43].
Comparing the transition energies with ones for similar com-
plex with amine-tert-butyl substituted phenol ligands [35] shows
that both transitions shifted to higher energies. It can attributed
to the electron-withdrawing effect of chlorine substituent on stabi-
C
16H10Cl5FeNO4 (510.84 g/mol): C, 37.21; H, 2.24; N, 3.00. Found:
C, 37.42; H, 2.00; N, 2.68. IR (KBr, cmꢂ1): 3428, 3083, 2957, 1591,
1455, 1378, 1297, 1219, 1170, 1079, 1024, 924, 864, 810, 765,
575, 478. UV–Vis in CH2Cl2: kmax, nm (e
, Mꢂ1 cmꢂ1): 289 (12800),
469 (2800). TOF-MSMS([FeLGDC +): m/z = 518.9.
lizing phenolate
p (HOMO) orbitals.
]
2.2.3. Spectrophotometric investigation of H3LGDC and Fe complexation
In an experiment, 2 mL of Fe(NO3)3ꢃ4H2O solution in methanol
(2.5 ꢁ 10ꢂ4 M) was transferred into a cuvette. UV–Vis spectra were
recorded in the range of 300–800 nm about 5 min after each addi-
3.1. Spectral data analysis of H3LGDC–Fe complexation
The titrations of ligand (H3LGDC) solutions have been conducted
at fixed concentration of iron and varying concentration of H3LGDC
.
tion of 10
l
L of H3LGDC (5 ꢁ 10ꢂ3 M) solution. Changes in the absor-
The titration spectra of iron nitrate upon increasing addition of
H3LGDC are shown in Fig. 1. During the titration, the hypochromic-
ity was observed without any shift in kmax band of 469 nm, which
represents the existence of interaction between H3LGDC and the
iron ion. The appearance of two isosbestic points in iron nitrate
spectra clearly indicates the existence of simple equilibrium be-
tween H3LGDC and FeLGDC. The complex composition of 1:1 was
determined by plotting the absorption changes vs. ligand to metal
mole ratio (nL/nFe). Fig. 2 shows a mole ratio plot of iron nitrate
upon increasing addition of H3LGDC. The observed spectral changes
were used to determine the binding constants using SQUAD
software. SQUAD program has been developed to enable the
bance of iron nitrate complex upon addition of H3LGDC solution
were monitored at the LMCT maximum wavelength of complexes.
2.2.4. Catalytic oxidation of 3,5-di-tert-butyl-catechol by FeLGDC
FeLGDC (with 5, 10, 50, 100 mmol percent) was added to a solu-
tion of triethylamine (2 mmol) in methanol 5 mL solvent (DMF,
acetonitrile, ethanol and methanol) and (1 mmol) 3,5-di-tert-bu-
tyl-catechol (3,5-DTBC). The solution exposed to dioxygen and stir-
red for 48 h, the violet color slowly changed to dark green. The
progress of the reaction was followed by TLC and 1H NMR spectros-
copy. Meanwhile both techniques showed the disappearance of

I. Saberikia et al. / Journal of Molecular Structure 1029 (2012) 60–67
63
3.2. ESI-MS of FeLGDC
The chemical compositions of complexes were established by
TOF-MSMS spectrometry. The ESI-MS spectrum gave a prominent
peak at m/z 500.89 [(FeLGDC)]+, which clearly indicated the forma-
tion of 1:1 complex between Fe and H3LGDC and a water molecule
correspondence to X-ray analysis and spectrophotometric titration
method (Section 3.1). The ion peak with lower intensity appeared
at m/z 518.9 is correspondence to FeLGDC complex including Fe
atom, H3LGDC and two water molecules. Furthermore, other peaks
in the mass spectrum revealed the pattern that began with the loss
of the carboxylic group (m/z 455.9) then a water molecule and CH2
methylene group (m/z 414.8), followed by loss of three chlorine
groups (m/z 316.9) after that iron and three oxygen atoms of phe-
nolates (m/z 198.96), then a phenyl group (m/z 133.05). The mass
spectrum of FeLGDC is given in Fig. 3. It is worth noting that this
ESI-MS, and consequently chemical composition is the same as
that for the similar iron(III) complex with amine-bis(tert-butyl
substituted phenolate), LGlyFe [35]. The TOF-MS spectrum gave
some [LGlyFe]+ ion peak at m/z 587.00 (Fig. 1S) correspondence to
the molecular weight of a 1:1 complex between Fe and H3LGly
Fig. 1. The titration absorption spectra of Fe(NO3)3ꢃ4H2O (2.5 ꢁ 10ꢂ4 M) by H3LGDC
.
including a water molecule. This difference (m/z LGlyFe–m/z
)
FeLGDC
is exactly the difference between molecular weights of four tert-
butyl and chlorine substituents. X-ray analysis of this complex
has revealed that in LGlyFe, the iron(III) center is surrounded by
the mentioned ligand while carboxylate group acts as bridging li-
gand for four coordinated iron centers of neighbor complexes lead-
ing to the formation of the infinite chains of the LGlyFe units [35].
Based on similarities of ESI-MS of both complexes one can predict
that FeLGDC has the same structure as LGlyFe.
3.3. X-ray crystal structure of FeLGDC
The diffraction experiment and the crystal data are summarized
in Table 1. The selected bond lengths and angles are given in Table
2.
Fig. 2. Determination of FeLGDC complex composition by the mole ratio plot.
The asymmetric part of the reported structure is composed of a
ferric center ligated by an H3LGDC ligand and a water molecule
coordinated to the metal as shown in Fig. 4.
evaluation of the best sets of binding constants from absorbance
measurements by employing a non-linear least squares approach
[44]. The input data consist of (a) the absorbance values and (b)
the total H3LGDC and Fe(NO3)3 concentrations.
The Gauss–Newton non-linear least-squares algorithm is used
for minimizing the residual sum of squares, U, which calculated
from the the following equation:
In the FeLGDC, each Fe ion has a FeNO4 coordination sphere
which has a 5-coordinate deformed geometry. The iron center is
surrounded by oxygen atoms O1, O2 of the phenolates and O3 of
carboxylate. An amine nitrogen N(1) and one oxygen atom O(4
or 40) of the coordinated water molecule occupy forth and fifth
positions. The phenolate O1 and O2 form short bonds to the Fe(III),
the distances being 1.913(15) and 1.922(16) Å, respectively. The
carboxylate O3 participates in the Fe1AO3 bond of 2.03(2) Å, while
the O(30) atom forms the 2.08(4) Å bond to the Fe1 at another prob-
ability level. The distances of the water molecule oxygen O4 from
Fe(III) is 1.94(2) Å while the other oxygen O(40) distance being
2.00(3) Å.
I
NW
ꢁ
ꢂ
XX
2
cal
i;k
obs
i;k
U ¼
A
ꢂ A
ð2Þ
i¼1 k¼1
obs
i;k
where A is the absorbance value of ith solution at kth wavelength,
give a total of I solutions and a grand total of NW wavelength. In our
experiments I = 15 and NW = 50.
The output data are the logarithm of macroscopic formation
constant (Kij) for formation of FeLGDC corresponding to the follow-
ing equilibrium,
The longest bond within the coordination sphere is formed by N1
atom, with the FeAN distance of 2.209(18) Å. Bond lengths are con-
sistent with iron complexes of aminophenol ligands [45,42,46–50].
The suggested structure is correspondence to the molecular mass.
H3LGDC þ FeðNO3Þ ꢃ 4H2O ! FeLGDC
ð3Þ
3.4. Geometry optimization calculations of FeLGDC
3
The values of U and percent of error represent uncertainty for
logKij calculated by the program.
As seen in metal coordination sphere (Fig. 4), two equal proba-
bilities exist for connecting the oxygen of carboxylate (O3, O30) or
water (O4, O40) to the Fe ion in FeLGDC complex. On the base of the
X-ray data of this complex, density functional theory (DFT) calcu-
lations have been performed using Gaussian 09 suite of programs
[51] for more insight into occupied atomic sites of the Fe coordina-
tion sphere. Two separate molecular structural optimizations in
correspond with two mentioned probabilities around of metal
The absorption data were analyzed by assuming 1:1 or 2:1 and/
or simultaneous 1:1 and 2:1 M ratios of H3LGDC to Fe(NO3)3. Fitting
of the experimental data (15 points), to the proposed stoichiome-
tric models was evaluated by the sum of squares of the calculated
points by the model. The results show that the best fitting
corresponds to the 1:1 complex model. The value of pKf has been
obtained 3.36 0.07 for FeLGDC complex.

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I. Saberikia et al. / Journal of Molecular Structure 1029 (2012) 60–67
Fig. 3. ESI–MS spectrum of FeLGDC
.
Table 2
Selected bond lengths (Å) and angles (°) for Fe2(LTHF)3.
O(4)AFe
1.94(2)
2.03(2)
2.00(3)
2.08(4)
1.922(16)
1.913(15)
2.209(18)
97.2(7)
O(4)AFeAO(3)
O(40)AFeAO(3)
O(2)AFeAO(30)
O(4)AFeAO(30)
O(40)AFeAO(30)
O(3)AFeAO(30)
O(1)AFeAO(30)
O(2)AFeAN(1)
O(1)AFeAN(1)
O(4)AFeAN(1)
O(40)AFeAN(1)
O(3)AFeAN(1)
O(30)AFeAN(1)
O(40)AFeAO(3)
O(4)AFeAO(3)
41.8(13)
95.0(13)
104.4(12)
91.3(7)
95.0(13)
69.2(12)
149.9(11)
89.5(7)
O(3)AFe
O(40)AFe
O(30)AFe
FeAO(2)
FeAO(1)
FeAN(1)
O(2)AFeAO(1)
O(2)AFeAO(4)
O(1)AFeAO(4)
O(2)AFeAO(40)
O(1)AFeAO(40)
O(4)AFeAO(40)
O(2)AFeAO(3)
O(1)AFeAO(3)
82.1(9)
91.3(7)
165.5(10)
95.3(11)
103.6(11)
62.2(12)
172.9(9)
87.6(8)
103.2(10)
163.6(11)
85.2(8)
68.6(10)
88.5(12)
94.5(11)
center have been carried out at the UB3LYP/6-311++Gꢀꢀ level. In
both initial molecular structures, the oxygen atom of water mole-
cule (O4 or O40) manually put at a distance of 2.5 Å from the Fe ion.
Some of bond lengths and angles around Fe center in the optimized
structures and their comparison with experimental X-ray values
for current Fe complex are summarized in Table 3. Except of the
expected differences originating from two types water definition
(see i and ii in Table 3) in calculations and two placements of the
O4 and O40 groups around the Fe ion, the differences between
other calculated bond lengths from the two calculations are
negligible and we report a single calculated value for each of the
bond length in Table 3. In general, the calculated bond lengths
and angles are in good agreement with X-ray experiment. When
3-atomic sites of water were considered in calculation (i), the
Fig. 4. ORTEP diagram and atom labeling scheme for the asymmetric unit of
complex LGlyFe. Ellipsoids are plotted at 50 probability level. Hydrogen atoms
omitted for clarity.
differences between corresponding calculated bond lengths,
Water(O4)AFe and Water(O40)AFe, with X-ray data are higher than
that of other applied calculation using single oxygen site as indica-
tor of water molecule (ii). In the next stage, to determine the

I. Saberikia et al. / Journal of Molecular Structure 1029 (2012) 60–67
65
Table 3
Comparison of selected bond lengths (Å) and angles (°) of FeLGDC complex from the
molecular geometry optimizations by UB3LYP method using 6-311++Gꢀꢀ basis set and
experimental X-ray structure.
Bond
Bond length (calc.) (Å)
Bond length (X-ray) (Å)
Phenolate(O1)AFe
Phenolate(O2)AFe
Carboxylate(O3)AFe
Carboxylate(O30)AFe
Water(O4)AFe
Water(O40)AFe
N1AFe
O1AC1
O2AC6
O3AC8
O30AC80
N1AC3
N1AC4
N1AC7
C1AC2
C1AC9
C6AC5
C6AC16
C8AC7
1.866
1.870
1.933
1.930
1.913(15)
1.922(16)
2.03(2)
2.08(4)
1.94(2)
2.00(3)
2.209(18)
1.33(2)
1.34(2)
1.55(5)
1.27(5)
1.48(3)
1.39(3)
1.48(3)
1.44(3)
1.43(3)
1.44(3)
1.36(3)
1.60(5)
1.189(19)
1.44(4)
1.158(14)
1.68(2)
1.711(19)
1.72(2)
1.68(2)
2.164a, 1.884b
2.155a, 1.884b
2.247
1.338
1.330
1.315
1.315
1.501
1.499
1.491
1.413
1.406
1.412
1.407
1.541
1.209
1.541
1.209
1.748
Fig. 5. Magnetic measurements for complex FeLGDC
.
the temperature-independent Larmor diamagnetic susceptibility
obtained from the Pascal’s tables [52,53] and for the sample holder
contribution. The magnetic diagram is presented in Fig. 5 in the
form of leff vs. T and as inverse susceptibility vs. T (inset).
C8AO5
C80AC7
C80AO50
Above T ꢅ 40 K, the effective magnetic moment (
complex FeLGDC is essentially temperature-independent and has
leff value of 5.43 B, which is close to the spin-only value of
leff) of the
Cl(1)AC9
Cl(2)AC11
Cl(3)AC16
Cl(4)AC14
1.757
1.750
1.757
l
5.92 lB for the isolated S = 5/2 Fe(III) ion. Thus the magnetic mea-
surement of this complex shows unambiguously that FeLGDC con-
tains the magnetically diluted high-spin d5 iron(III) ion.
Below 40 K, the effective magnetic moment (leff) slightly de-
creases. Decrease of the effective magnetic moment might be due
Angle
Bond angle (calc.) (°)
Bond angle, (X-ray) (°)
O1AFeAO2
O1AFeAN1
O2AFeAN1
FeAO1AC1
FeAO2AC6
C3AN1AC4
N1AC3AC2
N1AC4AC5
114.34a, 96.88b
89.14a, 81.47b
97.2(7)
91.3(7)
89.5(7)
123.5(10)
129.7(12)
107.7(19)
117.2(2)
120.2(18)
91.41a, 86.46b
119.4a, 129.61b
129.56a, 130.08b
113.14a, 113.07b
116.49a, 114.93b
116.25a, 115.12b
to a zero field splitting [52,53]. We applied a Curie–Weiss law
v
= C/(T ꢂ h) to fit the high temperature data (above 100 K) which
is shown as the inset in Fig. 5. The result (full line on the graph) al-
most passes the origin of the coordinate system showing the
Curie–Weiss temperature to be near h = 0.0 K. This result led us
to the conclusion that the contribution of zero field splitting in
the effective magnetic moment declines at low temperature.
a
The calculated bond length and angle when 3-atomic sites of water were
considered in calculation).
The calculated bond length and angle when the single oxygen site used as
indicator of water molecule in calculation).
b
3.6. Electrochemistry
Cyclic and differential pulse voltammograms (CV and DPV) of
the iron(III) complex were recorded in CH2Cl2 solutions containing
distortions of the real structure of the complex, all atomic sites
from X-ray data are frozen except of hydrogen atoms of the com-
plex and coordinated water molecule. We also determined the en-
ergy gap between HOMO and LUMO orbitals of FeLGDC complex
from the structure obtained in the calculations which are reported
in Table 4.
3.5. Magnetic susceptibility measurements
Magnetic susceptibility for powdered samples of FeLGDC was
measured in a magnetic field of 1000 Oe as a function of tempera-
ture in the range 2–300 K. The measured data were corrected for
Table 4
The total energy (in Hartree) and the energy gap (in eV) between HOMO and LUMO
orbitals of FeLGDC complex calculated at the UB3LYP/6-311++Gꢀꢀ level for two
probabilities (normal and prim (0) coordinating conditions shown in Fig. 4). In runs 2
and 20, all of non-hydrogen atomic sites of complex are frozen.
Run
Energy (a.u.)
HOMO–LUMO gap (eV)
a
b
Run-1 (full optimization)
Run-10 (full optimization)
Run-2 (frozen non-H sites)
Run-20 (frozen non-H sites)
ꢂ4152.8143834
ꢂ4152.8142501
ꢂ4152.6577175
ꢂ4152.7054438
0.17409
0.17398
0.14159
0.15526
0.09743
0.09816
0.07117
0.07106
Fig. 6. Cyclic voltammograms of FeLGDC (3 ꢁ 10ꢂ3 M) in CH2Cl2 with 0.1 M
[(nBu)4N]ClO4 as supporting electrolyte. Potentials are referenced vs. Fc, scan rate
is 50, 100, 200, 300, 400, 500 and 600 mV/s and T = ꢂ40 °C.

66
I. Saberikia et al. / Journal of Molecular Structure 1029 (2012) 60–67
Fig. 8. Distribution of cleavage products catalyzed by FeLGDC in methanol.
Table 5
Oxygenation cleavage products of catechol derivatives with FeLGDC complex as a
catalyst.
Fig. 7. Distribution of cleavage products catalyzed by FeLGDC in different solvents
(DMF, acetonitrile, ethanol and methanol).
Substrate
Solvent % Cleavage
products
% Other
products
%
0.1 M [(nBu)4N]ClO4 as supporting electrolyte. Prior to the mea-
Conversion
surement, the GC electrode was polished with 0.1 lm alumina
MeOH
98.21
1.79
100
OH
OH
powder and washed with distilled water. The voltage scan rate
was set at 50 mV sꢂ1. The solutions were deoxygenated by bub-
bling nitrogen gas through them for 10 min. Ferrocene was added
as an internal standard and potentials were referenced vs. the fer-
rocenium/ferrocene couple (Fc+/Fc).
The CV voltammogram (CV) observed for this complex revealed
oxidations and reductions peaks. In CH2Cl2 solution, this complex
exhibits irreversible anodic redox behavior in the positive potential
range assigned to the ligand-centered oxidation yielding the phe-
noxyl radical in the complex. The metal-centered voltammograms
have been observed in the negative potential range corresponding
with the Fe(III)/Fe(II) reduction of FeLGDC (Fig. 6). The CV voltam-
mograms with higher scan rates in low temperature show higher
cathodic and anodic currents due to lowering chemical side
reactions.
OH
OH
MeOH
93.40
84.80
85.94
6.60
15.20
14.06
100
100
100
OCH3
OH MeOH
H3C
OH
OH
OH
MeOH
Comparing the reduction potential of iron center in this com-
plex with the same tert-butyl substituted phenol-amine complex
[35] shows a positive shift in FeLGDC redox potential because of
more highly positive charge density on iron center due to elec-
tron-withdrawing effects of chlorine substituent.
genation of catechol family to cleavage products in the presence
of oxygen.
The oxidative cleavage reaction of catechol derivatives with this
complex was performed and the results are shown in Fig. 8 and
Table 5.
3.7. FeLGDC catalyzed oxygenation of catechol family
4. Conclusion
The focus of this experimental part was to catalyze the oxygen-
ation of catechols with different substituents with dioxygen as an
oxidant. In the presence of 5% of the catalyst, 100% of 3,5-di-tert-
butyl-catechol (3,5-DTBC) was converted to different cleavage
products. This observation was in contrast to our previous results
for the same reaction catalyzed by LGlyFe [35] in which 3,5-DTBC
was oxidized to produce 3,5-di-tert-butyl-o-benzoquinone (3,5-
DTBQ) as the major product. This criterion is attributed to the high-
er Lewis acidity of metal center in FeLGDC which facilitate oxidative
cleavage of catechols. Our UV–Vis spectra and electrochemical re-
sults confirm this claim.
The ligand [2-(bis(3,5-dichloro-2-hydroxybenzyl)amino)acetic
acid], H3LGDC was prepared by a simple synthesis. The iron(III)
complex of this tripodal tetradentate ligand was synthesized and
characterized.
The chemical compositions of iron(III) complex were estab-
lished by TOF-mass spectrometry and C, H, N analysis. Both tech-
niques confirm 1:1 ratio of ligand to iron nitrate. The optimized
structure of the complex from DFT calculation is in good agree-
ment with experimental X-ray funding.
The variable temperature magnetic susceptibility indicates that
FeLGDC is the paramagnetic high spin iron(III) complex in almost
the entire investigated temperature range. At low temperatures,
the effective magnetic moment slightly decreases which is very
probable due to the zero field splitting.
Progress of the reaction was followed by 1H NMR spectroscopy.
The signals of the free substrate (d = 6.90, 1.37, 1.23) disappeared
along with the appearance of another signals [44,45]. The reaction
was monitored with different solvents (MeOH, EtOH, CH3CN, DMF)
and catalyst weight to choose methanol as the best solvent and 5%
mmol of catalyst as proper loading of the catalyst. GC–MS tech-
nique was used to identify and quantify the oxidative products of
3,5-DTBC. The results are shown in Fig. 7.
Redox process of FeIIILGDC yielded the corresponding Fe(III)-phe-
noxyl radical and FeIILGDC species during the cyclic voltammetry
experiments. A study of the phenolate-to-Fe(III) charge transfer
band showed that substitution of a more electronegative substitu-
ent results in a red shift of the LMCT band and a positive shift of the
Fe(III)/(II) redox potential. As a result, the phenolate-to-Fe(III)
charge-transfer band indicates the redox potential of the iron
The 1H NMR and GC–mass show the 100% conversion of cate-
chols and lacking any oxidized quinone product. Finally, the results
show that FeLGDC complex can act as a good catalyst for the oxy-

I. Saberikia et al. / Journal of Molecular Structure 1029 (2012) 60–67
67
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ments show that FeLGDC complex acts as an excellent catalyst for
cleavage oxygenation of catechols in the presence of oxygen. These
observations will be helpful in designing proper ligands and mod-
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Authors are grateful to the Institute for Advanced Studies in Ba-
sic Sciences (IASBS), Changwon, Ljubljana and Messina Universities
for their valuable help. Special thanks to Dr. Saman Alavi for useful
comments and manuscript editing. E. Safaei gratefully acknowl-
edges the support by the Institute for Advanced Studies in Basic Sci-
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Appendix A. Supplementary material
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The structural data for FeLGDC has been deposited with the
Cambridge Crystallographic Data Centre, the deposition number
being CCDC 863642. This data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: +44 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.molstruc.2012.06.047.
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