Crystal structure of a μ-oxo-bridged dimeric iron(III) complex

Article abstract of DOI:10.1134/S0022476615080120

A dimeric [{Fe(5-ClL1)}₂(μ-O)], [H₂-5-ClL1 = N,N′-bis(5-chloro-2-hydroxybenzylidene)-2-methylpropane-1,2-diamine] tetradentate Schiff-base complex, 1, has been synthesized and its crystal structure has been determined by single crystal X-ray diffraction analysis. Structural analysis of complex 1 shows that the complex is a centrosymmetric dimer. Each of the Fe(III) ions has a five-coordinate geometry and one oxygen atom bridges two Fe(III) ions to form a μ-oxo structure. The geometry around iron atom can be described as a square based pyramid with the FeN₂O₂ coordination plane and oxo ligand.

Full text of DOI:10.1134/S0022476615080120

Journal of Structural Chemistry. Vol. 56, No. 8, pp. 1540-1544, 2015.
Original Russian Text © 2015 Y. Yahsi, E. Gungor, C. Kazak, H. Kara.
CRYSTAL STRUCTURE OF A µ-OXO-BRIDGED
DIMERIC IRON(III) COMPLEX
Y. Yahsi1, E. Gungor1, C. Kazak2, and H. Kara1,3
UDC 541.49:546.72:548.73
A
dimeric
[{Fe(5-ClL1)}2(μ-O)],
[H2-5-ClL1 = N,N′-bis(5-chloro-2-hydroxybenzylidene)-2-
methylpropane-1,2-diamine] tetradentate Schiff-base complex, 1, has been synthesized and its crystal
structure has been determined by single crystal X-ray diffraction analysis. Structural analysis of complex 1
shows that the complex is a centrosymmetric dimer. Each of the Fe(III) ions has a five-coordinate geometry
and one oxygen atom bridges two Fe(III) ions to form a μ-oxo structure. The geometry around iron atom
can be described as a square based pyramid with the FeN2O2 coordination plane and oxo ligand.
DOI: 10.1134/S0022476615080120
Keywords: synthesis, Schiff-base ligands, iron(III) complexes, X-ray crystal structure analysis, oxo
bridged structure.
INTRODUCTION
Oxygen-bridged binuclear iron complexes have been of considerable interest for several decades, due to their
various interesting structural, electronic, magnetic and spectroscopic properties [1-14]. In recent times, a great deal of
attention has been paid to studies on synthesis and characterization of diiron(III) complexes because of their role in the fields
of bioinorganic, organometallic, and catalytic chemistry due to their importance as synthetic models for the oxidation
catalysts [15-17], bistable molecular materials based on temperature-, pressure- or light-induced spin-crossover behavior
[18, 19] and iron-containing enzymes such as methane monooxygenase, ribonucleotide reductase and purple acid
phosphatases [20-24]. In addition, low-nuclearity complexes, such as Fe2 and Fe3, are likely to represent the “molecular
nanoscale bricks” for the formation of high-nuclearity molecular clusters and hence studies on their structural
characterization and various properties are essential steps for a correct approach to larger systems [25-28]. In general oxygen-
bridged diiron(III) complexes fall into four classes, oxo-bridged [29-36], hydroxo-bridged [30, 35-40], alkoxo-bridged
[41-44] and phenoxo bridged [8, 14, 45-47] species.
Recently our research group reported the structural and magnetic characterization of mononuclear and phenoxo-
bridged binuclear iron(III) complexes containing tetradentate Schiff base ligands with O, N, N, O, donor set [14, 45]. In view
of the importance of Fe(III) complexes and our interest in the characterization of transition metal complexes containing
Schiff base ligands, we report here the synthesis and single crystal X-ray structure of a μ-oxo-bridged binuclear iron(III)
complex, [{Fe(5-ClL1)}2(μ-O)], [H2-5-ClL1 = N,N’-bis(5-Chloro-2-hydroxybenzylidene)-2-methylpropane-1,2-diamine], 1.
The structure is dimeric in which two metal ions are connected by oxo-oxygen atoms.
1
Balikesir University, Faculty of Art and Science, Department of Physics, Balikesir, Turkey; yahsi@balikesir.edu.tr.
2 3
Ondokuz Mayis University, Faculty of Art and Science, Department of Physics, Samsun, Turkey. Department of Physics,
Faculty of Science, Mugla Sikti Koçman University, Mugla, Turkey. The text was submitted by the authors in English.
Zhurnal Strukturnoi Khimii, Vol. 56, No. 8, pp. 1601-1605, December, 2015. Original article submitted May 27, 2014.
1540
0022-4766/15/5608-1540 © 2015 by Pleiades Publishing, Ltd.

EXPERIMENTAL SECTION
Preparation of complex 1. The ligand H2-5-ClL1 (N,N’-bis(5-Chloro-2-hydroxybenzylidene)-2-methylpropane-
1,2-diamine) was prepared by reaction of 1,2-diamino-2-methylpropane (1 mmol, 0.088 g) with 5-chlorosalicylaldehyde
(2 mmol, 0.312 g) in hot ethanol (100 mL). The yellow product of the ligand was precipitated from solution on cooling. The
complex 1 was prepared by the addition of FeCl3 (1 mmol, 0.162 g) in 30 mL of hot methanol to the ligand (1 mmol, 0.369 g)
in 30 mL of hot methanol. This solution has been warmed to 60°C and stirred for 2 h. The resulting solution has been filtered
rapidly and then allowed to stand at room temperature. Several weeks of standing have led to the growth of red crystals of 1
suitable for X-ray analysis.
Scheme 1. Schematic diagram of complex 1.
X-ray structure determination. Diffraction measurement was made on a Stoe-IPDS-2 diffractometer (at 296 K
for 1) using graphite monochromated MoKα radiation (λ = 0.71073 Å). Data collection and cell refinement: Stoe X-AREA
[48] and data reduction: Stoe X-RED [48] for 1. The structure was solved by direct methods and refined using full-matrix
least-squares against F2 using SHELXL [49]. All non-hydrogen atoms were assigned anisotropic displacement parameters
and refined without positional constraints. Hydrogen atoms were included in idealized positions with isotropic displacement
parameters constrained to 1.5 times the Ueq of their attached carbon atoms for methyl hydrogens, and 1.2 times the Ueq of
their attached carbon atoms for all others. The crystal data and structure refinement details for complex 1 are listed in
Table 1. Selected bond lengths and angles are summarized in Table 2. Molecular structure of complex 1 is shown in Fig. 1,
while packing diagram is given in Fig. 2.
TABLE 1. Crystal Data and Structure Refinement of Complex 1
CCDC No.
Chemical formula
Mw
834942
C36H32Cl4Fe2N4O5
854.16
Crystal system
Triclinic
Space group
P-1
Unit cell dimensions a, b, c, Å
α, β, γ, deg
7.4543(10), 10.8357(15), 12.0391(17)
70.115(10), 84.819(11), 87.802(11)
3
V, Å
910.7(2)
293(2)
1
T, K
Z
3
1.557
ρcalc, g/cm
–1
1.138
μ, mm
Reflections collected / independent
R1 [I > 2σ(I)]
15569 / 4318
0.0559
0.1492
wR2 (all data)
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TABLE 2. Some Selected Bond Lengths (Å) and Angles (deg) for Complex 1
Bond lengths Bond angles
85.46(16)
Fe1—O1
Fe1—O2
Fe1—O3
Fe1—N1
Fe1—N2
1.933(4)
1.906(4)
1.7604(9)
2.095(4)
2.114(4)
1.7604(9)
O1—Fe1—N1
O1—Fe1—N2
O2—Fe1—N1
O2—Fe1—N2
O2—Fe1—O1
O3—Fe1—O1
O3—Fe1—O2
O3—Fe1—N1
O3—Fe1—N2
N1—Fe1—N2
103.84(13)
106.24(12)
103.61(13)
100.61(12)
75.81(17)
180.00(5)
152.08(17)
148.10(17)
87.83(16)
97.99(16)
*
*
Fe1 —O3—Fe1
O3—Fe1
RESULTS AND DISCUSSION
Structural Analysis of [{Fe(5-ClL2)}2(μ-O)], 1. Complex 1 is the μ-oxo-bridged dinuclear Fe(III) complex. The
asymmetric unit of 1 contains one [{Fe(5-ClL2)}2(μ-O)] molecule. It crystallizes in the triclinic space group P-1. The
bridging oxo group O3 lies on the crystallographic center of symmetry. The four coordinating atoms N1, N2, O1 and O2 are
nearly coplanar (Fig. 1). The metal center Fe1 deviates from the mean plane towards the apical oxo-bridge by 0.474 Å. The
structural distortion index of 1 were found τFe1 = 0.169, indicate that Fe1 and Fe1* polyhedron are all close to distorted
square-pyramidal. The basal plane of the square pyramid (Fe1) is formed by N2O2 donors from the 5-ClL2 ligand and the
axial position is occupied by a bridging oxygen atom. Also, the FeN2O2 coordination plane in each iron(III) is oriented trans
III
III
to the other relative to the oxo bridge in order to avoid interligand steric repulsions. The Fe ⋯Fe separation (3.521 Å)
compares favorably with the corresponding distances observed in related μ-oxo-monobridged dinuclear complexes of
iron(III) (3.39-3.62 Å) [26, 30, 50, 51]. The bond lengths between the metal and donor atoms in the base of the pyramid are
as follows: Fe–Nimine, 2.095(4)-2.114(4) Å; Fe–Ophenolic, 1.933(4)-1.906(4) Å. The Fe–(μ–O) bond distance is 1.7604 Å,
which is shorter than those reported for other μ-oxo complexes [52, 53]. These observed geometrical features of iron(III)
centers in 1 are quite comparable to those of the similar dinuclear complexes reported in the literature [52-73].
CONCLUSIONS
New dinuclear Fe(III) complex has been obtained with the tetradentate Schiff base ligand. We report here the
synthesis and structural determination of μ-oxo-bridged Fe(III) dimer complex, 1. The molecular structure of 1 has been
successfully determined by single crystal X-ray diffraction. In complex 1, each of the two Fe(III) ions has a five-coordinate
structure and one oxygen atom bridges two Fe(III) ions to form a μ-oxo structure.
Fig. 1. The molecular structure of 1.
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Fig. 2. Molecular packing diagram in the ac-plane of complex 1.
CIF file containing complete information on the studied structure was deposited with CCDC, deposition number
834942, and is freely available upon request from the following web site: www.ccdc.cam.ac.uk/data_request/cif.
The authors are grateful to the Research Funds of Balikesir University (BAP-2012/91) and TUBITAK (Grants No:
TBAG-108T431) for the financial support.
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