Synthesis and crystal structure of a new dinuclear iron(III) complex: [Fe2O(PhCO2)2(2,2′-bpy) 2(N3)2]?H2O

Article abstract of DOI:10.1002/zaac.201000081

By using a precursor complex [Fe₃O(PhCO₂) ₆(H₂O)₃]NO₃ as starting material and 2,2′-bpy (= 2,2′-bipyridine) as rigid chelating ligand, the new dinuclear iron-oxido complex [Fe₂O(PhCO₂) ₂(2,2′-bpy)₂(N₃)₂]?H ₂O (1) was synthesized and structurally characterized. The reaction of [Fe₃O(PhCO₂)₆(H₂O) ₃]NO₃ with 2,2′-bpy and sodium azide in 1:3:3 ratio gave the dinuclear complex 1, whereas a 1:6:3 ratio reaction system only gave the complex [Fe(2,2′-bpy)₃]³⁺, which indicated that 2,2′-bipyridine plays a crucial function in the nuclear forming procedure. Meanwhile, the N₃^- ligands take up the chelating domain of oxygen and reduce the nucleation. Different π-π interactions exist in 1, which extend its structure to a three dimensional supramolecular framework.

Full text of DOI:10.1002/zaac.201000081

ARTICLE
DOI: 10.1002/zaac.201000081
Synthesis and Crystal Structure of a New Dinuclear Iron(III) Complex:
[Fe2O(PhCO2)2(2,2'-bpy)2(N3)2]·H2O
Qing-Ran Wu,[a] Chuan-Qin Du,[a] Huai-Ming Hu,*[a] and Bing Xu[a]
Keywords: 2,2'-Bipyridine; Oxido complexes; X-ray diffraction; Iron; Bioinorganic chemistry
Abstract. By using a precursor complex [Fe3O(PhCO2)6(H2O)3]NO3 ratio reaction system only gave the complex [Fe(2,2'-bpy)3]3+, which
as starting material and 2,2'-bpy (= 2,2'-bipyridine) as rigid chelating indicated that 2,2'-bipyridine plays a crucial function in the nuclear
–
ligand, the new dinuclear iron-oxido complex [Fe2O(PhCO2)2(2,2'- forming procedure. Meanwhile, the N3 ligands take up the chelating
bpy)2(N3)2]·H2O (1) was synthesized and structurally characterized. domain of oxygen and reduce the nucleation. Different π–π interactions
The reaction of [Fe3O(PhCO2)6(H2O)3]NO3 with 2,2'-bpy and sodium exist in 1, which extend its structure to a three dimensional supramo-
azide in 1:3:3 ratio gave the dinuclear complex 1, whereas a 1:6:3 lecular framework.
in the presence of carboxylic groups, with or without other
Introduction
Significant developments in the chemistry of oxygen-bridged
chelating ligands, proved to be a very useful method for ob-
taining both oxide and hydroxide containing clusters. This ap-
polynuclear iron complexes initially resulted from discovery
proach resulted in a number of complexes with diverse nucle-
of the biological role of oxygen-bridged poly-iron centers [1].
uses and Fex topological arrangements [23–24].
Proteins containing carboxylate-bridged diiron active sites per-
In the last several years we have been very interested in de-
form a variety of biochemical functions [2, 3]. The active sites
veloping 3d metal coordination cluster chemistry with oxide
in some metalloprotein systems such as hemerythrin [4, 5],
bridges and predominant carboxyl peripheral ligation. The
methane monooxygenase [6, 7], and ribonucleotide reductase
presence of chelating ligands was found to have profound ef-
[8] may contain diiron cores, where the iron site can transfer
fects on the nucleuses and metal topology of the resultant pro-
II
from Fe2 to Fe2III. It is very surprising that the remarkably
ducts. Many synthetic procedures of polynuclear iron clusters
similar structures can exhibit various functions of these pro-
rely on the reaction of [Fe3O(O2CR)6L]+ species with poten-
teins. Studies on the synthesis of these model complexes to
tially chelating ligands [25–29], and we thus also explored this
model the iron proteins were carried out and suggested how
starting material for reactions with 2,2'-bpy, which acts as a
important they play a role in biological systems. As a result of
rigid chelation ligand for the synthesis of the Fe2O complex,
these and other stimuli, a wide variety of such complexes with
[Fe2O(PhCO2)2(2,2'-bpy)2(N3)2]·H2O (1). We have also ex-
aesthetically pleasing structures and interesting magnetic prop-
plored the use of sodium azide in such reactions. Herein we
erties were prepared and studied over the last 15 years [9–18].
report the synthesis and structure of complex 1.
The azide ligand showed a good ability to act as bridging sev-
eral metals and to induce ferromagnetic exchange interactions
between the paramagnetic metal atoms [19, 20]. Several poly-
Results and Discussion
Synthesis
nuclear clusters with large-spin ground state were prepared in
a variety of coordination modes by substituting alkoxido or
hydroxido bridges with azido bridges [21, 22].
The use of 2,2'-bpy in iron(III) chemistry yielded a variety
The continuing development of the above areas promotes the
of new dinuclear and hexanuclear iron complexes [30]. There
discovery of new synthetic procedures to obtain new structural
was one reason to believe that stable Fe2O2/PhCO2/bpy com-
types. One approach is to use selected chelates to encourage
plexes should be synthetically feasible if the correct procedures
aggregation, while ensuring discrete products that are soluble
could be discovered. Herein we described one method to ob-
–
and can be purified and crystallized. Hydrolysis of iron salts
tain stable Fe2O2/PhCO2/bpy complexes by introducing N3 to
the system.
* Prof. Dr. H.-M. Hu
The reaction of [Fe3O(PhCO2)6(H2O)3]NO3 with 2,2'-bpy
and sodium azide in a 1:3:3 ratio in MeCN gave red crystals
of the new dinuclear complex 1. The use of 2,2'-bpy drastically
destroys the Fe3O structure of the starting material for its bi-
dentate chelating function. It indicates that 2,2'-bpy plays a
determining function in the nuclear forming procedure. Mean-
Fax: +86-29-88303331
E-Mail: ChemHu1@nwu.edu.cn
[a] Key Laboratory of Synthetic and Natural Functional Molecule
Chemistry of Ministry of Education
College of Chemistry and Materials Science
Northwest University
Xi'an 710069, P. R. China
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Q.-R. Wu, C.-Q. Du, H.-M. Hu, B. Xu
ARTICLE
while, the N3 anions take up the chelating domain of oxygen the bridged atom O3 with FeIII is the shortest. The Fe···Fe dis-
and reduce the nucleation. The reaction is shown in Scheme 1. tance (3.120 Å) is similar to those of the typical distances of
However, a 1:6:3 ratio of [Fe3O(PhCO2)6(H2O)3]NO3/2,2'-bpy/ dinuclear species with one oxido and two carboxylic bridges
NaN3 in the reaction system gave the complex [Fe(2,2'- [31]. In the crystal structure of 1 there are three types of π···π
bpy)3]3+, which indicates that the ratio of reactants is very im- stacking interactions: (1) π(2,2'-bpy)···π(2,2'-bpy)i (i = 1/2–x, 1/
–
portant.
2–y, 1–z), centroid–centroid distance = 3.814 Å, dihedral an-
gle = 3.45°; (2) π(2,2'-bpy)ii···π(2,2'-bpy)iii (ii = –x, y, 1/2–z;
iii = x–1/2, 1/2–y, z–1/2), plane–plane distance = 3.54 Å; (3)
π(C12–17)···π(C12-C17)iv, π(C12–17)v···π(C12-C17)vi, (iv = –
x, –y, 2–z; v = –x, y, 3/2–z; vi = x, –y, z–1/2), plane–plane
distance = 3.152 Å and one type of C–H···π interaction: C9–
H9···π(C12–17)vii (vii = –x, y, 2.5–z), H···π distance = 2.882 Å,
C–H···π angle = 151.96°. The molecules are packed together
through the first type of π···π stacking interactions to form 1D
infinite chains (Figure 2). The adjacent chains are parallel to
each other and further linked by the second type of π···π stack-
ing interactions and the C–H···π interactions to form a sheet
along the b axis (Figure 3a). The sheet shows butterfly-shaped
chains along the a axis (Figure 3b) and bowl-shaped chains
Scheme 1. Formation of 1.
Crystal Structure
Single-crystal X-ray analysis reveals that complex 1 crystalli-
zes in monoclinic system, space group C2/c, with one Fe3+ cat-
ion, one O2– anion, one PhCO2 anion, one azide anion, one
–
2,2'-bpy molecule, and one lattice water molecule in the asym-
metric unit. As shown in Figure 1, the neutral molecule con-
tains a [Fe2O]4+ core bridged by two PhCO2– groups. Each FeIII
atom coordinates to three nitrogen atoms from one bidentate
chelating 2,2'-bpy ligand and one azide anion and three oxygen
atoms from two benzoate and one central O2– anion with dis-
torted octahedral arrangement. The Fe–O bond lengths range
from 1.785 to 2.123 Å. It is noteworthy that the bond length of
Figure 3. Perspective view of the 2D sheet formed by π–π stacking
Figure 1. ORTEP drawing of 1 with thermal ellipsoids at 30 % proba- interactions and the C–H···π interactions along the b axis (a), the a
bility level, hydrogen atoms are omitted for clarity.
axis (b) and the c axis (c).
Figure 2. The 1D infinite chain forming through the π–π stacking interactions.
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Z. Anorg. Allg. Chem. 2010, 2471–2474

A New Dinuclear Iron(III) Oxido Complex
along the c axis (Figure 3c). These sheets are parallel to each carboxyl groups in 1 [34]. The strong absorption band at
other and further linked by the third type of π···π stacking inter- 834 cm–1 may be assigned to the νas (Fe–O–Fe) stretching vi-
actions along the a axis to form a 3D supramolecular structure brations of the oxido-bridged dinuclear iron complexes [35,
(Figure 4a). Another interesting feature of the structure of 1 is 36].
that the bowls of the adjacent sheets are arrange top to top
along the c axis to produce a grid pore with a size of
Conclusions
5.732 × 17.202 Å and bottom to bottom to produce a grid pore
with a size of 3.558 × 7.938 Å (Figure 4b). There are some
intermolecular interactions in the crystal structure of 1: C1–
H1···O3, 3.060 Å, 115.4°; C10–H10A···O2, 3.120 Å, 118.1°;
O4W···N3, 2.941 Å; C7–H7···N4i, 3.477 Å, 151.9°; C4–
H4···N3i, 3.536 Å, 148.0° (i = 1/2–x, 1/2–y, 1–z). These hydro-
gen bonds are helpful to stabilize the crystal packing in 1.
In summary, the appropriate ratios of the ligands 2,2'-bpy
–
and N3 proved to be a very useful route to form a Fe2O com-
plex from a Fe3O complex. The results presented in this work
–
further illustrate the values of 2,2'-bpy and N3 in reactions
with FeIII reagents as tools to induce the nucleation. The use
of the ligand 2,2'-bpy and sodium azide in iron(III) carboxyl
chemistry continues to provide access to interesting supramo-
lecular assemblies of dinuclear units. Both the present and pre-
vious results thus suggest that the well-defined polynuclear
iron carboxyl complexes may serve as models for lower nucle-
ation species in both synthetic and biological systems.
Experimental Section
Materials and General Methods
[Fe3O(PhCO2)6(H2O)3]NO3 was synthesized according to the literature
[37]. Sodium azide and solvents were commercially available and used
as received without further purification. 2,2'-bpy was purchased from
Alfa Aesar and used without further purification. Elemental analyses
(C, H, N) were determined with a Vario EL III elemental analyzer.
The FT-IR spectra were recorded from KBr pellets in the range 4000–
400 cm–1 with a Bruker EQUINOX-55 spectrometer.
Synthesis
[Fe2O(PhCO2)2(2,2'-bpy)2(N3)2]·H2O (1): To a stirred solution of
2,2'-bpy (0.0519 g, 0.33 mmol) in MeCN (5 mL) was added
[Fe3O(PhCO2)6(H2O)3]NO3 (0.103 g, 0.1 mmol) and sodium azide
(0.0215 g, 0.33 mmol). After being stirred under aerobic conditions at
ambient temperature for 8 hours, the reaction mixture was left over-
night at room temperature and afterwards filtered. The filtrate was left
undisturbed by slowly evaporation. The block red crystals of 1 formed
after one week, they were collected by filtration and air dried. Yield
0.0392 g, ca. 50 % (based on Fe). Anal. C34H28Fe2N10O6: calcd. C
52.06; H 3.60; N 17.86 %; found: C 52.01; H 3.63; N 17.88 %. FT-
Figure 4. Perspective view of the 3D supramolecular structure through
the π–π interactions between the phenyl rings along the a axis (a) and
the c axis with two kinds of pores (b).
IR (KBr): ν = 3447 (w), 2053 (s), 1597 (s), 1547 (s),1492 (s), 1443
˜
(m), 834 (s) cm–1.
X-ray Crystallography
IR Spectrum
The band at 3447 cm–1 in the IR spectrum of 1 may be as-
signed to the O–H stretching vibrations of the lattice water
molecules. The band at 2053 cm–1 may be assigned to the
stretching vibrations of the azide anions. The bands at 1597
and 1492 cm–1 belong to the azide anions [32, 33]. The νas
(COO) vibration is identified by the strong band at 1547 cm–1,
the band at 1443 cm–1 is assigned to the νs (COO) vibration.
The separation between the νas (COO) and νs (COO) band in
Intensity data for complex 1 were collected with a Bruker Smart APEX
II CCD diffractometer with graphite-monochromated Mo-Kα radiation
(λ = 0.71073 Å) at room temperature. Empirical absorption corrections
were applied by the SADABS program. The structure was solved by
direct methods and refined by the full-matrix least-squares based on F2
using the SHELXTL-97 program [38]. All non-hydrogen atoms were
refined anisotropically and the hydrogen atoms of organic ligands were
generated geometrically. Crystallographic data and other details on the
refinements are summarized in Table 1. Selected bond lengths and an-
1 amounts 104 cm–1, which confirms the bridging mode of the gles are listed in Table 2.
Z. Anorg. Allg. Chem. 2010, 2471–2474
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Q.-R. Wu, C.-Q. Du, H.-M. Hu, B. Xu
ARTICLE
Table 1. Crystal data and structural refinement parameters for 1.
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C34H28Fe2N10O6
784.36
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D /Mg·m–3
1.270
μ /mm–1
0.759
F(000)
1608
λ (Mo-Kα) /Å
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0.71073
10203
3626
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S on F2
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Fe(1)–N(3)
Fe(1)–N(1)
1.785(2)
2.039(5)
2.149(4)
Fe(1)–O(2)#1
Fe(1)–O(1)
Fe(1)–N(2)
2.034(3)
2.123(4)
2.211(4)
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96.46(18)
95.70(13)
167.83(18)
O(2)#1–Fe(1)–N(3) 92.90(18)
O(2)#1–Fe(1)–O(1) 84.36(15)
O(3)–Fe(1)–N(1)
N(3)–Fe(1)–N(1)
O(3)–Fe(1)–N(2)
N(3)–Fe(1)–N(2)
N(1)–Fe(1)–N(2)
O(3)–Fe(1)–O(1)
N(3)–Fe(1)–O(1)
94.03(15)
92.95(19)
O(2)#1–Fe(1)–N(1) 162.37(15)
O(1)–Fe(1)–N(1)
86.43(15)
167.96(15) O(2)#1–Fe(1)–N(2) 89.99(15)
85.19(18)
73.96(16)
O(1)–Fe(1)–N(2)
Fe(1)–O(3)–Fe(1)#1 121.9(3)
82.96(14)
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Acknowledgement
This work was supported by the National Natural Science Foundation
of China (Grant Nos. 20573083 and 20873098).
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Received: February 9, 2010
Published Online: May 26, 2010
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Z. Anorg. Allg. Chem. 2010, 2471–2474