Synthesis, structures, and magnetic behavior of two high-spin binuclear Fe(III) complexes

Article abstract of DOI:10.1080/00958972.2011.586032

The reaction of 2-t-butyl-4-ethylphenol, formaldehyde, and 2-amino propanol or 3-amino-1-propanol at 2 : 2 : 1 provides N-(1-ethanol)-N,N-bis(3-t-butyl-5- ethyl-2-hydroxybenxyl)amine (H3L') and N-(3-amino-1-propanol)-N,N-bis(3-t-butyl- 5-ethyl-2-hydroxybenxyl)amine (H3L″), respectively. In the presence of Et3N, the reaction of FeCl3 6H2O and H3L′ or H3L″ gives dinuclear Fe(III) complexes [Fe₂L′₂] 1 and [Fe ₂L″₂] 2, respectively, which have been characterized by X-ray crystallography, magnetic measurements, and cyclic voltammetry (CV). Magnetic studies indicate significant antiferromagnetic coupling between the iron(III) centers for 1 and 2. The values obtained for the coupling constants (J) are -12.35 cm^-1 for 1 and -16.26 cm^-1 for 2. CVs of 1 and 2 reveal one reversible wave at -0.80 and -0.82 V versus AgCl/Ag, respectively, which can be ascribed to redox coupling of Fe^IIIFe ^II/Fe^IIIFe^III.

Full text of DOI:10.1080/00958972.2011.586032

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Synthesis, structures, and magnetic behavior of
two high-spin binuclear Fe(III) complexes
Jin-Ye Chen , Yun-Li Liu , Wei-Quan Xu , Er-Xuan He & Shu-Zhong Zhan
To cite this article: Jin-Ye Chen , Yun-Li Liu , Wei-Quan Xu , Er-Xuan He & Shu-
Zhong Zhan (2011) Synthesis, structures, and magnetic behavior of two high-spin
binuclear Fe(III) complexes, Journal of Coordination Chemistry, 64:15, 2606-2617, DOI:
10.1080/00958972.2011.586032
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Date: 19 October 2015, At: 00:10

Journal of Coordination Chemistry
Vol. 64, No. 15, 10 August 2011, 2606–2617
Synthesis, structures, and magnetic behavior of two high-spin
binuclear Fe(III) complexes
JIN-YE CHEN, YUN-LI LIU, WEI-QUAN XU, ER-XUAN HE
and SHU-ZHONG ZHAN*
College of Chemistry & Chemical Engineering, South China University of Technology,
Guangzhou 510640, China
(Received 2 January 2011; in final form 12 April 2011)
The reaction of 2-t-butyl-4-ethylphenol, formaldehyde, and 2-amino propanol or 3-amino-
1-propanol at 2 : 2 : 1 provides N-(1-ethanol)-N,N-bis(3-t-butyl-5-ethyl-2-hydroxybenxyl)amine
(H3L0) and N-(3-amino-1-propanol)-N,N-bis(3-t-butyl-5-ethyl-2-hydroxybenxyl)amine (H3L00),
respectively. In the presence of Et3N, the reaction of FeCl3 ꢀ 6H2O and H3L0 or H3L00 gives
dinuclear Fe(III) complexes [Fe2L02]
1
and [Fe2L020] 2, respectively, which have been
characterized by X-ray crystallography, magnetic measurements, and cyclic voltammetry
(CV). Magnetic studies indicate significant antiferromagnetic coupling between the iron(III)
centers for 1 and 2. The values obtained for the coupling constants (J) are ꢁ12.35 cmꢁ1 for 1
and ꢁ16.26 cmꢁ1 for 2. CVs of 1 and 2 reveal one reversible wave at ꢁ0.80 and ꢁ0.82 V versus
AgCl/Ag, respectively, which can be ascribed to redox coupling of FeIIIFeII/FeIIIFeIII
.
Keywords: Dinuclear Fe(III) complexes; Crystal structures; Magnetic properties;
Electrochemical properties
1. Introduction
The dinuclear iron complexes of chelating alkoxide and aryl-oxide ligands have
attracted considerable interest as models of metalloenzymes and redox catalysts, as well
as the mechanistic understanding of spin-coupled systems [1–7]. Particular interest has
been directed toward the exchange phenomena in di- and polynuclear complexes, which
have led to essential insights into magneto-structural correlations [8–10]. It is well
known that in O-bridged systems the M–O–M angle plays a vital role in determining the
nature of magnetic exchange between the metal ions [11].
The study of magnetic exchange mechanisms between metal centers will be useful in
finding suitable building blocks for the assembly of new magnetic materials and in the
development of new redox catalysts. An approach toward this important goal is the
design and preparation of unique ligands that impart novel chemistry to the metal
coordination sphere. The use of different bridging and polydentate ligands has afforded
an impressive array of coordination complexes with new architectures. Among them,
chelating phenolates have attracted our attention, as these compounds have remarkable
*Corresponding author. Email: shzhzhan@scut.edu.cn
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2011.586032

Binuclear Fe(III) complexes
tBu
2607
tBu
t Bu
tBu
OH
HO
OH
HO
N
N
Et
Et
Et
Et
OH
H3L'
OH
H3L"
Scheme 1. Structures of new ligands.
bridging ability to afford multinuclear complexes potentially useful for the development
of new magnetic materials and catalysts [12–17].
H3L0 and H3L00 (scheme 1) have been prepared by the reactions of 2-t-butyl-4-
ethylphenol, formaldehyde and 2-amino propanol or 3-amino-1-propanol. The0reaction
of FeCl3 ꢀ 6H2O and H3L0 or H3L00 gives dinuclear Fe(III) complexes [Fe2L2] 1 and
[Fe2L020] 2, respectively. As part of our research in this area, we describe the synthesis,
structure determination, magnetic properties, and electrochemical properties of 1 and 2.
2. Experimental
All solvents and reagents were obtained in high purity from commercial sources and
used as received unless noted otherwise.
2.1. Physical measurements
Electronic spectra were recorded on a Hitachi U-3010 (UV-Vis) spectrophotometer
for solutions in CH3CN. 1H NMR spectra were measured on a Bruker AM 500
spectrometer in CDCl3. Magnetic susceptibility data for powder samples were collected
from 2 to 300 K with a Quantum Design SQUID Magnetometer MPMS XL-7.
Effective magnetic moments were calculated by the equation ꢀeff ¼ 2.828(ꢁMT)1/2
,
where ꢁM is the molar magnetic susceptibility. Electrochemical experiments were
carried out with an Auto Lab instrument with a platinum wire as the working electrode,
a platinum plate as the counter electrode, and a AgCl/Ag electrode as the reference
electrode. For experiments performed in CH3CN (ca 1.1 ꢂ 10ꢁ5 mol Lꢁ1) containing
0.1 mol Lꢁ1 tetra-n-butylammonium perchlorate (TBAP) as supporting electrolyte, the
potential was referenced to a AgCl/Ag electrode.
2.2. Synthesis
2.2.1. Synthesis of H3L0. A solution of 2-t-butyl-4-ethylphenol (8.92 g, 50 mmol) in
ethanol (50 ml) was mixed with 2-aminoethanol (1.53 g, 25 mmol). A 37% aqueous
formaldehyde (4.5 ml, 50 mmol) was added and the mixture was refluxed for 12 h.

2608
J.-Y. Chen et al.
The reaction mixture was filtered and the solid was purified by crystallization from
ethanol to obtain yellow crystals, which were collected and dried in vacuo (1.86 g, 17%).
Calcd for C28H43NO3 (%): C, 76.19; H, 9.75; N, 3.18. Found (%): C, 76.01; H, 9.58; N,
3.21. 1H NMR (CDCl3, ppm): ꢂ 7.02 (s, 2H, Ar), 6.74 (s, 2H, Ar), 3.86 (t, 2H, –O–CH2),
3.75 (s, 4H, –N–CH2 ꢂ 2), 2.73 (t, 2H, –N–CH2), 2.52 (quart, 4H, –CH2 ꢂ 2), 2.08 (s,
1H, –OH), 1.40 (s, 18H, t-Bu ꢂ 2), 1.19 (t, 6H, –CH3 ꢂ 2). UV-Vis [CH3CN, ꢃmax/nm
("/L molꢁ1 cmꢁ1)]: 230 (2.1 ꢂ 104), 283 (7.58 ꢂ 103).
2.2.2. Synthesis of H3L00. The procedure was performed in the same way as that for
the synthesis of H3L0 except that 2-aminoethanol was replaced by 3-amino-1-propanol.
H3L00 was obtained in 26% (2.95 g). Calcd for C29H45NO3 (%): C, 76.48; H, 9.89; N,
3.08. Found (%): C, 76.17; H, 9.58; N, 3.05. 1H NMR (CDCl3, ppm): ꢂ 7.01 (s, 2H, Ar),
6.75 (s, 2H, Ar), 6.11 (s, 2H, –OH ꢂ 2), 3.75 (t, 2H, –O–CH2), 3.64 (s, 4H, –N–CH2 ꢂ 2),
2.65 (t, 2H, –N–CH2), 2.54 (quart, 4H, –CH2 ꢂ 2), 1.39 (s, 18H, t-Bu ꢂ 2), 1.19 (t, 6H, –
CH3 ꢂ 2). UV-Vis [CH3CN, ꢃmax/nm ("/L molꢁ1 cmꢁ1)]: 240 (9.7 ꢂ 103), 283 (1.4 ꢂ 104).
2.2.3. Synthesis of 1. To a solution, containing H3L0 (0.44 g, 1.0 mmol) and
triethylamine (0.30 g, 3.0 mmol) in C2H5OH (25 ml), FeCl3 ꢀ 6H2O (0.270 g, 1.0 mmol)
was added; the color of the solution changed from yellow to deep red. The solution was
allowed to slowly evaporate to give red crystals, which were collected and dried in vacuo
(0.26 g, 46%). Calcd for C28H40FeNO3 (%): C, 68.04; H, 8.10; N, 2.83. Found (%): C,
67.81; H, 8.02; N, 2.87. UV-Vis [CH3CN, ꢃmax/nm ("/L molꢁ1 cmꢁ1)]: 230 (1.3 ꢂ 104),
280 (1.23 ꢂ 104), 326 (6.9 ꢂ 103), 431 (4.0 ꢂ 103).
2.2.4. Synthesis of 2. The procedure was performed in the same way as that for the
synthesis of 1 except that H3L0 was replaced by H3L00. Complex 2 was obtained in 50%
(0.31 g). Calcd for C29H42FeNO3 (%): C, 68.52; H, 8.27; N, 2.76. Found (%): C, 67.97;
H, 8.22; N, 2.77. UV-Vis [CH3CN, ꢃmax/nm ("/L molꢁ1 cmꢁ1)]: 242 (1.1 ꢂ 104), 281
(1.21 ꢂ 104), 328 (6.4 ꢂ 103), 437 (4.3 ꢂ 103).
2.3. X-ray crystallography
Data were collected with a Bruker SMART CCD area detector using graphite-
˚
monochromated Mo-Ka radiation (0.71073 A) at 113 K. All empirical absorption
corrections were applied by using SADABS [18]. The structures were solved using
direct methods and the corresponding non-hydrogen atoms were refined anisotrop-
ically. All hydrogens of the ligands were placed in calculated positions with fixed
isotropic thermal parameters and included in the structure factor calculations in the
final stage of full-matrix least-squares refinement. All calculations were performed
using SHELXTL [19]. Table 1 lists details of the crystal parameters, data collection,
and refinement for 1 and 2; selected bond distances and angles for 1 and 2 are listed
in tables 2 and 3.

Binuclear Fe(III) complexes
2609
Table 1. Crystallographic data for 1 and 2.
Parameter
1
2
Empirical formula
Formula weight
L (A)
Crystal system
Space group
Unit cell dimension (A, )
C28H40FeNO3
494.46
0.71073
Monoclinic
P2(1)/c
C29H42FeNO3
508.49
0.71073
˚
Triclinic
ꢀ
P1
ꢃ
˚
a
b
c
ꢄ
ꢅ
ꢆ
13.411(3)
10.101(2)
10.964(2)
13.266(3)
85.93(3)
83.78(3)
68.56(3)
1358.7(5), 2
1.243
546
1.54–25.02
14,051/4782
4782/0/315
1.039
8.6214(17)
22.936(5)
90.00
90.17(3)
90.00
2651.9(9), 4
1.238
1060
2.33–25.02
20,938/4661
4661/0/307
1.070
3
˚
Volume (A ), Z
Calculated density (Mg mꢁ3
F(000)
ꢇ range for data collection
)
Reflections collected/unique
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I 4 2ꢈ(I)]
R indices (all data)
R1 ¼ 0.0361; wR2 ¼ 0.1014
R1 ¼ 0.0714; wR2 ¼ 0.1482
R1 ¼ 0.0408; wR2 ¼ 0.1049
R1 ¼ 0.1137; wR2 ¼ 0.1733
ꢃ
˚
Table 2. Selected bond distances (A) and angles ( ) for 1.
Fe(1)ꢁO(2)
Fe(1)ꢁO(3)
Fe(1)ꢁN(1)
1.8539(14)
1.9737(13)
2.1683(16)
Fe(1)ꢁO(1)
1.8595(14)
1.9813(14)
Fe(1)ꢁO(3)#
O(2)ꢁFe(1)ꢁO(1)
O(1)ꢁFe(1)ꢁO(3)
O(1)ꢁFe(1)ꢁO(3)#1
Fe(1)–O(3)–Fe(1)#1
119.48(6)
119.64(6)
101.82(6)
104.20(6)
O(2)–Fe(1)–O(3)
O(2)–Fe(1)–O(3)#1
O(3)–Fe(1)–O(3)#1
120.42(6)
98.96(6)
75.80(6)
Symmetry transformations used to generate equivalent atoms: #1 ꢁx + 1, ꢁy + 1, ꢁz + 1.
ꢃ
˚
Table 3. Selected bond distances (A) and angles ( ) for 2.
Fe(1)ꢁO(1)
Fe(1)ꢁO(3)
Fe(1)ꢁN(1)
1.849(3)
1.957(3)
2.196(4)
Fe(1)ꢁO(2)
1.870(3)
2.024(3)
Fe(1)ꢁO(3)#1
O(1)ꢁFe(1)ꢁO(2)
O(2)ꢁFe(1)ꢁO(3)
O(2)ꢁFe(1)ꢁO(3)#1
Fe(1)ꢁO(3)ꢁFe(1)#1
112.47(14)
132.31(13)
97.01(13)
104.79(13)
O(1)ꢁFe(1)ꢁO(3)
O(1)ꢁFe(1)ꢁO(3)#1
O(3)ꢁFe(1)ꢁO(3)#1
115.17(14)
97.19(13)
75.21(13)
Symmetry transformations used to generate equivalent atoms: #1 ꢁx + 1, ꢁy + 1, ꢁz.
3. Results and discussion
3.1. Synthesis and characterization
The reaction of 2-t-butyl-4-methylphenol, formaldehyde, and 2-aminoethanol provided
1
H3L0 in 17% yield (Supplementary material, figure S1. H NMR spectrum of H3L0).

2610
J.-Y. Chen et al.
t Bu
t Bu
O
Et
Et
t Bu
t Bu
HO
OH
O
Fe
O
O
O
Et3N
N
N
Fe
1
N
FeCl3 6H2O
Et
O
Et
OH
t Bu
t Bu
Et
Et
CH2O
NH2(CH2)2OH
t Bu
OH
2
Et
NH2(CH2)3OH
t Bu
t Bu
O
Et
Et
CH2O
t Bu
t Bu
HO
OH
O
Fe
O
O
O
Et3N
N
N
Fe
2
N
FeCl3 6H2O
O
Et
Et
t Bu
t Bu
Et
Et
OH
Scheme 2. Schematic representation of the synthesis of ligands and complexes 1 and 2.
The reaction of 2-t-butyl-4-methylphenol, formaldehyde, and 3-amino-1-propanol
1
gave H3L00 in 26% yield (Supplementary material, figure S2. H NMR spectrum of
H3L00). Both H3L0 and H3L00 contain a potential [O3N] donor set, and can afford L03ꢁ or
3ꢁ
L00 anionic ligands when deprotonated.
In the presence of triethylamine, the reaction of FeCl3 ꢀ 6H2O and H3L0 or H3L00 gave
two dinuclear Fe(III) complexes, 1 and 2, respectively (scheme 2).
3.2. Electronic spectra
The electronic spectra of H3L0, H3L00, 1, and 2 were recorded in CH3CN at room
temperature (table 4). As shown in figures S3–S4, H3L0 exhibited bands at 230 and
283 nm, and H3L00 showed bands at 240 and 283 nm. Compared with those of H3L0
and H3L00, two new absorption bands of 1 appeared at 326 and 431 nm. The lower
energy band can be assigned to a phenolate pꢉ to FeIII dꢉ* charge transfer (CT)
transition, and the higher energy band is attributed to a phenolate p to FeIII dꢈ*
CT [20, 21].
Similar to 1, complex 2 also showed bands at 328 and 437 nm, which can be
attributed to phenolate to FeIII CT.

Binuclear Fe(III) complexes
2611
Table 4. Photo-physical and electrochemical data for H3L0, H3L00, 1, and 2 in CH3CN.
CH3CNa
CH3CN ꢃabs (nm)
Eox1
Ered1
Ered2
H3L0
H3L00
1
230, 283
240, 283
230, 280, 326, 431
242, 281, 328, 437
–
–
–
–
–
–
ꢁ0.72
ꢁ0.88
ꢁ1.43b
ꢁ1.56b
2
ꢁ0.72
ꢁ0.91
aPotential in V vs. Ag/AgCl at 40 mV sꢁ1
.
bPeak potential for irreversible wave.
Figure 1. Molecular structure of 1.
3.3. Crystal structures
3.3.1. Crystal structure of 1. As shown in figure 1, the molecular structure of 1 is
3ꢁ
formed by two L0 and two irons. The irons are linked by two hydroxy oxygens. The
coordination environment around iron is a distorted trigonal bipyramid. Iron is bonded
to two phenolate oxygens (O(2), O(3)), two hydroxy oxygens (O(1), O(10)), and one
amine nitrogen (N(1)). The Fe–O bond distances fall in the range 1.8539(14)–
˚
˚
˚
1.9813(14) A. The Fe–N distance (2.1683 A) is slightly longer (0.0183 A) than that
˚
reported for octahedral Fe–N distance of 2.15 A [22]. Two iron centers are separated by
˚
3.121 A, a value that is similar to those found in other oxygen-bridged dinuclear iron

2612
J.-Y. Chen et al.
Figure 2. Molecular structure of 2.
˚
complexes [23, 24]. The Fe–Oalkoxo bond distances (1.9737(13) and 1.9813(14) A) of 1
are inequivalent, as observed in other bis(m-alkoxo) complexes [7, 25–30]. The bridging
plane containing Fe(1), O(3), Fe(10), O(30) is planar with the torsion angle O(30)–Fe(1)–
O(3)–Fe(10) of 0o. The Fe(1)–O(3)–Fe(10) angle is 104.20ꢃ.
3.3.2. Crystal structure of 2. Similar to 1, 2 is also formed by two L003ꢁ and two irons.
Iron is bonded to two phenolate oxygens (O(1), O(2)), two hydroxy oxygens (O(3),
O(30)), and one amine nitrogen (N(1)) (figure 2). Irons are linked by two hydroxy
oxygens. The Fe(1)–O(1), Fe(1)–O(2), Fe(1)–O(3), and Fe(1)–O(30) bond distances are
˚
1.849(3), 1.870(3), 1.957(3), and 2.024(3) A, respectively. The amine nitrogen Fe–N
˚
distance (2.196(4) A) is slightly shorter (0.0277 A) than that of 1. Iron centers are
˚
˚
separated by 3.154 A, slightly longer (0.033 A) than that of 1. The average Fe–Oalkoxo
˚
˚
˚
distance (1.9905 A) is longer than that (1.9775 A) of 1. The bridging plane containing
Fe(1), O(3), Fe(10), O(30) is planar with torsion angle O(30)–Fe(1)–O(3)–Fe(10) of 0ꢃ. The
Fe(1)–O(3)–Fe(10) angle is 104.79ꢃ, slightly larger (0.59ꢃ) than that (104.20ꢃ) of 1. Some
important structural data of related complexes are listed in table 5 for comparison.
3.4. Magnetic properties of 1 and 2
The magnetic properties of 1 and 2 were examined from 2 to 300 K. As shown in
figure 3, the value of ꢀeff at room temperature (7.35 mB) is less than the expected spin-
P
only value (8.37 mB) of two high spin (hs) Fe3þ (S ¼ 5/2) ions [ꢀ ¼ g[ ZS(S þ 1)]1/2],

Binuclear Fe(III) complexes
2613
Table 5. Structural and magnetic data for some bis(m-alkoxo)diiron(III) complexes.
Fe–O–Fe (ꢃ)
Pa (A)
J (cmꢁ1
)
Ref.
˚
Fe–Fe (A)
˚
Complex
[Fe2(bbpnol)2]
[Fe2(L)2]b
3.125
3.14
101.1
102.8
103.0
103.6
104.3
104.6
104.54
105.51
104.20
104.8
2.024
2.0345
1.995
1.982
1.991
2.002
1.987
1.977
1.978
1.991
ꢁ2.2
ꢁ15.4
ꢁ16.3
ꢁ11.0
ꢁ15.4
ꢁ10.9
ꢁ13.35
ꢁ13.58
ꢁ12.35
ꢁ16.26
[25]
[26]
[27]
[28]
[28]
[29]
[30]
[7]
[Fe2L(OMe)Cl2]c
[Fe2(acac)4(OEt)2]d
[Fe2L(OEt)Cl2]c
[Fe2(L)2(OMe)2]e
[Fe2L2]
3.106
3.116
3.144
3.168
3.143
3.142
3.121
3.154
[Fe2L02
[Fe2L02]
[Fe2L020]
]
This work
This work
aHalf of the shortest super-exchange pathway between two iron(III) ions. H3bbpnol ¼ N,N0-bis(2-
hydroxybenzyl)-2-hydroxypropane-1,3-diamine.
bH2L ¼ [2-(((2-(3,5-di-tert-butyl-2-hydroxybenzylamino)ethyl)
(2-hydroxyethyl)amino)methyl)-4,6-di-tert-
butylphenol].
cH3L ¼ 1,4-Piperazinediyl-bis(N-ethylenesalicylaldimine).
dacac ¼ Pentane-2,4-dionate.
eH2L ¼ pimelyl-bis(N-isopropylhydroxamicacid). H3L2 ¼ N-(1-propanol)-N,N-bis-((3-tert-butyl-5-methyl-2-
hydroxybenxyl)amine. H3L02 ¼ N-(1-ethanol)-N,N-bis(3-tert-butyl-5-methyl-2-hydroxybenxyl)amine.
0.05
0.04
0.03
0.02
0.01
0.00
0
100
200
300
T/K
Figure 3. Plot of the temperature dependence of the ꢁM for 1.
indicating that there are strong interactions between Fe3þ ions. The effective magnetic
moment (ꢀeff) decreases abruptly with cooling to a minimum value of 0.19 mB at 2 K.
Assuming isotropic exchange, the experimental magnetic data are simulated for the
dimeric Fe(III) system based on the spin Hamiltonian H ¼ ꢁ2JS1S2 with the following
equation (S1 ¼ S2 ¼ 5/2) [31]:
ꢁM ¼ ð2Nꢅ2g2=kT Þ½ð55 þ 30 expðꢁ10J=kT Þ þ 14 expðꢁ18J=kT Þ þ 5 expðꢁ24J=kT Þ
þ expðꢁ28J=kT ÞÞ=ð11 þ 9 expðꢁ10J=kT Þ þ 7 expðꢁ18J=kT Þ þ 5 expðꢁ24J=kT Þ
þ 3 expðꢁ28J=kT Þ þ expðꢁ30J=kT ÞÞꢄ
Very good agreement between the theoretical and experimental data is obtained
ð1Þ
by using the following parameters: g ¼ 2.0, J ¼ ꢁ12.35 cmꢁ1
,
normal for

2614
J.-Y. Chen et al.
0.028
0.026
0.024
0.022
0.020
0.018
0.016
0.014
0.012
0.010
0.008
0
100
T/K
200
300
Figure 4. Plot of the temperature dependence of the ꢁM for 2.
antiferromagnetic interaction of (m-alkoxo)diiron(III) complexes. The coupling con-
stant J has been reported to be ꢁ11 to ꢁ26 cmꢁ1 for mono- and bis(m-alkoxo)diiron(III)
complexes [32–35].
The magnetic behavior of 2 is shown in figure 4 in the form of ꢁM versus T.
The value of ꢀeff at room temperature (6.86 mB) is less than the expected spin-only
value (8.37 mB) of two high-spin (hs) Fe3þ (S ¼ 5/2) ions. The effective magnetic
moment (ꢀeff) decreases abruptly with cooling to a minimum value of 0.50 mB
at 2 K.
The experimental magnetic data can also be reproduced by equation 1. Very good
agreement between the theoretical and experimental data is obtained by using the
following parameters: g ¼ 2.0, J ¼ ꢁ16.26 cmꢁ1
.
As shown in table 5, the value of J is influenced by the Fe–O–Fe angle and the
˚
˚
shortest super-exchange pathway (P/A) between two iron(III) ions (P/A). The value of
ꢁJ increases with an increased Fe–O–Fe angle and a decreased pathway between two
˚
iron(III) ions (P/A) [23, 25]. There is stronger magnetic coupling between iron(III) ions
in 2 than 1, because of larger Fe–O–Fe angle in 2.
3.5. Electrochemical properties
The electrochemical properties of 1 and 2 were measured by cyclic voltammetry (CV)
in CH3CN (table 4 and figures 5–6).
Complexes 1 and 2 exhibit one or two redox waves and followed the order 1 (ꢁ1.43
and ꢁ0.80 V) ! 2 (ꢁ1.56 and ꢁ0.82 V). These are also in accord with the trend of the
lowest-energy absorption spectra of 1 (431 nm) and 2 (437 nm).
Complex 1 shows two redox couples, at ꢁ1.43 and ꢁ0.80 V versus AgCl/Ag, which
can be ascribed to successive redox coupling of FeIIFeII/FeIIIFeII and FeIIIFeII/
FeIIIFeIII, respectively. Complex 2 shows two redox couples, at ꢁ1.56 and ꢁ0.82 V
versus AgCl/Ag, which is also ascribed to successive redox coupling of FeIIFeII/FeIIIFeII
and FeIIIFeII/FeIIIFeIII.

Binuclear Fe(III) complexes
2615
20
10
III II
III
Fe Fe
2Fe
0
–10
–20
–30
–2.0 –1.5 –1.0 –0.5 0.0
E/V
0.5
1.0
1.5
2.0
Figure 5. CV of 1 in CH3CN/0.1 mol Lꢁ1 [Bu4N]ClO4 at 40 mV sꢁ1 scan rate.
10
III II
III
Fe Fe
2Fe
0
–10
–20
–30
–40
–2.0 –1.5 –1.0 –0.5 0.0
E/V
0.5
1.0
1.5
2.0
Figure 6. CV of 2 in CH3CN/0.1 mol Lꢁ1 [Bu4N]ClO4 at 40 mV sꢁ1 scan rate.
4. Conclusions
Two high-spin binuclear Fe(III) complexes have been synthesized and characterized by
X-ray crystallography and magnetic measurements. Similar high-spin iron(III)
complexes with chlorokojic acid or kojic acid have been reported [36, 37]. The present
studies show that the Fe–O–Fe bridge and the shortest super-exchange pathway
between two iron(III) ions have great impact on determining structural parameters with
small changes in the bridging unit leading to good results for a multitude of structural
variations. Therefore, we can use different numbers of phenolate groups to design
multidentate ligands. We have built two high-spin dinuclear iron(III) complexes in
which the structure can be controlled by the design of bridged ligands. Currently, we are
exploring this line for other metals.

2616
J.-Y. Chen et al.
Supplementary material
CCDC 802131 and 802132 contain the supplementary crystallographic data for this
article. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; Fax: (þ44) 1223-336-033; or E-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgments
This work was supported by the Research Foundation for Returned Chinese Scholars
Overseas of Chinese Education Ministry (No. B7050170), the National Science
Foundation of China (No. 20971045), the Student Research Program (SRP) of South
China University of Technology and Analytical and Testing Center of South China
University of Technology.
References
[1] D.M. Kurtz. Chem. Rev., 90, 585 (1990).
[2] B.J. Wallar, J.D. Lipscomb. Chem. Rev., 96, 2625 (1996).
[3] E.I. Solomon, T.C. Brunold, M.I. Davis, J.N. Kemsley, S.K. Lee, N. Lehnert, F. Neese, A.J. Skulan,
Y.-S. Yang, J. Zhou. Chem. Rev., 100, 235 (2000).
[4] J. Du Bois, T.J. Mizoguchi, S. Lippard. Coord. Chem. Rev., 200–202, 443 (2000).
[5] E.Y. Tshuva, S.J. Lippard. Chem. Rev., 104, 987 (2004).
[6] G.J.P. Britovsek, V.C. Gibson, D.F. Wass. Angew. Chem., Int. Ed., 38, 428 (1999).
[7] X.-W. Tan, B.-M. Wang, Y. Wang, S.-Z. Zhan. Inorg. Chem. Commun., 13, 1061 (2010).
[8] S.M. Gorun, S.J. Lippard. Inorg. Chem., 30, 1625 (1991).
[9] J. Jullien, G. Juhasz, P. Mialane, E. Dumas, C.R. Mayer, J. Marrot, E. Riviere, E.L. Bominaar,
E. Munck, F. Secheresse. Inorg. Chem., 45, 6922 (2006).
[10] E. Labisbal, L. Rodriguez, O. Souto, A. Sousa-Pedrares, J. Garcia-Vazquez, J. Romero, A. Sousa,
M. Yanez, F. Orallob, J. Real. Dalton Trans., 8644 (2009).
[11] L.K. Thompson, S.K. Mandal, S.S. Tandon, J.N. Bridson, M.K. Park. Inorg. Chem., 35, 3117 (1996).
[12] E.Y. Tshuva, M. Versano, I. Goldberg, M. Kol, H. Weitman, Z. Goldschmidt. Inorg. Chem. Commun., 2,
371 (1999).
[13] L.P. Rothwell. Acc. Chem. Res., 21, 153 (1988).
[14] S.W. Schweiger, D.L. Tillison, M.G. Thorn, P.E. Fanwick, I.P. Rothwell. Dalton Trans., 2401 (2001).
[15] M.J. Caulfield, T. Russo, D.H. Solomon. Aust. J. Chem., 53, 545 (2000).
[16] B. Castellano, E. Solari, C. Florian, N. Re, A. Chiesi-Villa, C. Rizzoli. Chem. Eur. J., 5, 722 (1999).
[17] H. Nie, S.M.J. Aubin, M.S. Mashuta, C.-H. Wu, J.F. Richardson, D.N. Hendrickson, R.M. Buchanan.
Inorg. Chem., 34, 2382 (1995).
[18] G.M. Sheldrick. SADABS, Program for Empirical Absorption Correction of Area Detector Data,
University of Gottingen, Gottingen, Germany (1996).
¨
[19] G.M. Sheldrick. SHELXS 97, Program for Crystal Structure Refinement, University of Gottingen,
¨
¨
Gottingen, Germany (1997).
¨
[20] B.P. Gaber, V. Miskowski, T.G. Spiro. J. Am. Chem. Soc., 96, 6868 (1974).
[21] A. Neves, M.A. deBrito, I. Vencato, V. Drago, K. Griesar, W. Haase. Inorg. Chem., 35, 2360 (1996).
[22] R.E. Norman, R.C. Holz, S. Menage, L. Que Jr., J.H. Zhang, C.J. O’Connor. Inorg. Chem., 29, 4629
(1990).
[23] R. Werner, S. Ostrovsky, K. Griesar, W. Haase. Inorg. Chim. Acta, 326, 78 (2001).
[24] A. Horn Jr, I. Vencato, A.J. Bortoluzzi, R. Horner, R.A. Nome Silva, B. Spoganicz, V. Drago,
¨
H. Terenzi, M.C.B. de Oliveira, R. Werner, W. Haase, A. Neves. Inorg. Chim. Acta, 358, 339 (2005).
[25] A. Neves, L.M. Rossi, I. Vencato, W. Haase, R. Werner. Dalton Trans., 707 (2000).
ˇ ´
[26] E. Safaei, I. Saberikia, A. Wojtczak, Z. Jaglicic, A. Kozakiewicz. Polyhedron, 30, 1143 (2011).

Binuclear Fe(III) complexes
2617
[27] J.A. Bertrand, J.L. Breece, P.G. Eller. Inorg. Chem., 13, 125 (1974).
[28] B. Chiari, O. Piovesana, T. Tarantelli, P.F. Zanazzi. Inorg. Chem., 21, 1396 (1982).
[29] S. Menage, L. Que Jr. Inorg. Chem., 29, 4293 (1990).
[30] X. Tan, J. Chen, X. Xie, S. Zhan, Y. Deng. Transition Met. Chem., 35, 999 (2010).
[31] J.T. Wrobleski, D.B. Brown. Inorg. Chem., 17, 2959 (1978).
[32] J.D. Walker, R. Poli. Inorg. Chem., 29, 756 (1990).
[33] S. Menage, L. Que Jr. Inorg. Chem., 29, 4293 (1990).
[34] B. Krebs, K. Schepers, B. Bremer, G. Henkel, E. Althaus, W. Muller-Wannuth, K. Griesar, W. Haase.
Inorg. Chem., 33, 1907 (1994).
[35] L.-J. Ming, H.G. Jang, L. Que Jr. Inorg. Chem., 31, 359 (1992).
[36] K. Hryniewicz, K. Stadnicka, A. Adamski, A. Pattek-Janczyk. J. Coord. Chem., 63, 977 (2010).
[37] K. Zaremba, W. Lasocha, A. Adamski, J. Stanek, A. Pattek-Janczyk. J. Coord. Chem., 60, 1537 (2007).