Inorganic Chemistry Communications 7 (2004) 584–587
www.elsevier.com/locate/inoche
Synthesis and characterization of a new iron(III) oxide
cluster containing two different discrete [Fe3O] units:
[Fe3O(O2CCH@CHACH3)6(H2O)3][Fe3O(O2CCH@CHAH3)7
(H2O)2](HO2CCH@CHACH3)4(OH)(H2O) q
Kou-Lin Zhang
a
a,*
, Yu-Jun Shi b, Song Gao c, Yao-Dong Dai d,
Kai-Bei Yu e, Xiao-Zeng You d,*
Chemistry and Chemical Engineering College, Yangzhou University, Ximen Street, Yangzhou, 225002, P.R. China
b
Department of Chemistry, Nantong Teachers University, Nantong, 226007, P.R. China
c
College of Chemistry and Molecular Engineering, Peking University, Peking, 100871, P.R. China
d
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, 210093, P.R. China
e
Chengdu Branch of Chinese Academy of Science, Analysis Center, Chengdu, 610041, P.R. China
Received 3 February 2004; accepted 19 February 2004
Published online: 12 March 2004
Abstract
A new complex containing two different discrete trinuclear oxo-centered [Fe3 O] units has been synthesized and characterized by
single crystal X-ray diffraction analysis and M€
ossbauer spectra. The M€
ossbauer spectra of the complex are typical of high spin
iron(III) complexes.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Synthesis; New iron(III) oxide cluster; Crystal structure; M€
ossbauer spectra
Researchers have made efforts to design and synthesize the new molecule-based magnets because they exhibit polyfunctional solid-state properties [1–8]. Among
these, the polynuclear iron-oxo complexes are receiving
much attention. One of the fascinating aspects of the
investigation of large iron clusters is that of providing
models for the biomineralization of iron, which leads to
such diverse compounds as magnetite and ferritin [9–13].
The recent discovery that iron-oxo clusters offer the
potential of acting as precursors to molecule-based
magnetic materials and even of functioning as nanoscale magnetic particles that they may display novel
properties intermediate between those of simple paraq
Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.inoche.2004.02.024.
*
Corresponding authors. Tel.: +8605147869171; fax: +860514797
5520.
E-mail address: [email protected] (K.-L. Zhang).
1387-7003/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2004.02.024
magnets and bulk magnets has added more interest in
this area [14–16]. Over the past few years, a great
number of such clusters with aesthetically pleasing
structures and interesting magnetic properties have been
synthesized and studied. Among them, oxo-centered
carboxylate-bridged trinuclear iron(III) complexes of
general formula [Fe3 (l3 -O)(O2 CR)6 L3 ]z (z ¼ 0, +1) have
been synthesized and structurally characterized for a
long time [17,18]. Attention has been focused almost
exclusively on various properties of these complexes in
the solid state. The highly symmetrical structure and the
relatively large metal–metal distances, which exclude the
possibility of direct metal–metal bonding make these
attractive systems with which to examine magnetic and
electronic interactions [18]. The mono cationic complexes which contain three high-spin iron(III) centers
were some of the first polynuclear systems to which
ideas of magnetic exchange were applied [19]. As an
extension to the above areas, we have been investigating
K.-L. Zhang et al. / Inorganic Chemistry Communications 7 (2004) 584–587
new synthetic procedures capable of allowing access to
new structural types. Our interests are mainly focused
on the molecular-based magnets [20,21]. In this paper,
we report the preparation, crystal structure and
M€
ossbauer spectra of the title complex. As far as we
know, this is the first case that contains two different
discrete Fe3 O units in the same complex.
The reaction [22] of excess trans-2-butenoic acid with
FeSO4 7H2 O in the presence of NaOH gives the new
complex [Fe3 O(O2 CCH@CHACH3 )6 (H2 O)3 ][Fe3 O(O2 CCH@CHACH3 )7 (H2 O)2 ](HO2 CCH@CHACH3 )4 (OH)
(H2 O). The X-ray analysis reveals [23] that the complex
contains two different discrete Fe3 O units, one OH anion, one water molecule and four free trans-2-butenoic
acid molecules. The formulae of the two trinuclear oxocentered units are [Fe3 O(O2 CC@CHACH3 )6 (H2 O)3 ]þ
(unit 1, Fig. 1) and [Fe3 O(O2 CC@CHACH3 )7 (H2 O)2 ]
(unit 2, Fig. 2), respectively.
The unit 1 is a Fe3 O description. It carries a positive
charge. The Fe(4)–O(18) and Fe(6)–O(18) distances are
almost the same, but the Fe(5)–O(18) distance is slightly
Again comparing the Fe–O (H2 O)
shorter [1.886(3) A].
distances, we can see that the bond lengths of Fe(4)–
while
O(27) and Fe(6)–O(33) are the same (2.053(4) A),
the Fe(5)–O(32) distance of 2.093(4) A is obviously
longer than the former two. The triangle composed of
the Fe(4), Fe(5) and Fe(6) atoms is very close to an
equilateral triangle, with Fe(4)–Fe(5), Fe(5)–Fe(6) and
Fe(4)–Fe(6) distances of 3.29(6), 3.27(2) and 3.30(6) A,
respectively. The Fe(5)–Fe(6)–Fe(4), Fe(4)–Fe(5)–Fe(6)
and Fe(5)–Fe(4)–Fe(6) angles are 60.1°, 60.4° and 59.4°,
respectively. The central oxygen atom O(18) lies slightly
and angles
Fig. 1. The structure of the unit 1. Chief bond lengths (A)
(°): Fe(4)–O(18) 1.914(3), Fe(5)–O(18) 1.886(3), Fe(6)–O(18) 1.901(3);
O(27)–Fe(4)–O(18) 178.68(17), O(25)–Fe(4)–O(21) 171.18(15), O(19)–
Fe(4)–O(23) 170.02(17), O(18)–Fe(5)–O(32) 177.55(17), O(28)–Fe(5)–
O(20) 169.11(16), O(30)–Fe(5)–O(22) 167.17(15), O(29)–Fe(6)–O(26)
168.16(16), O(24)–Fe(6)–O(31) 170.93(18), O(18)–Fe(6)–O(33)
175.69(16).
585
and angles
Fig. 2. The structure of the unit 2. Chief bond lengths (A)
(°): Fe(1)–O(1) 1.872(3), Fe(2)–O(1) 1.951(3), Fe(3)–O(1) 1.904(3);
O(1)–Fe(1)–O(10) 178.30(15), O(2)–Fe(1)–O(6) 167.46(16), O(8)–
Fe(1)–O(4) 166.03(16), O(1)–Fe(2)–O(15) 178.87(15), O(11)–Fe(2)–
O(3) 172.44(16), O(13)–Fe(2)–O(5) 176.03(16), O(1)–Fe(3)–O(17)
178.09(17),
O(12)–Fe(3)–O(9)
169.21(16),
O(14)–Fe(3)–O(7)
170.02(16).
The Fe(III)
above the Fe(4)Fe(5)Fe(6) plane (0.0094 A).
coordination geometry is slightly distorted octahedron
with a terminal water oxygen atom, an oxygen atom in
the center of the triangle and any other four oxygen
atoms from the bridging carboxylate groups completing
the coordination to each metal atom.
In unit 2, the Fe(1)Fe(2)Fe(3) triangle is also very
close to an equilateral triangle, with Fe(1)–Fe(3), Fe(2)–
Fe(3) and Fe(1)–Fe(2) distances of 3.26(2), 3.33(8) and
respectively. The Fe(1)–Fe(2)–Fe(3), Fe(2)–
3.31(9) A,
Fe(1)–Fe(3) and Fe(1)–Fe(3)–Fe(2) angles are 58.7°,
61.0° and 60.4°, respectively. The central oxygen O(1)
atom lies slightly below the Fe(1)Fe(2)Fe(3) plane
The Fe(1) and Fe(3) coordination geometry
0.0087 A.
can be described as slightly distorted octahedron with
four oxygen atoms from the bridging carboxylate
groups, one terminal water oxygen atom and an oxygen
atom in the center of the triangle completing the coordination to each metal atom. The Fe(2) coordination
geometry is also a slightly distorted octahedron with
four oxygen atoms from the bridging carboxylate
groups, one oxygen atom from the unidentate carboxylate group and an oxygen atom in the center of the
triangle completing the coordination to the atom. The
whole unit (2) carries no charge.
To our knowledge, although there are many oxocentered carboxylate-bridged triiron complexes that
have been prepared and structurally characterized
[17,18], this is the first case that contains two different
discrete Fe3 O units in the same compound. The distance
between O(1) and O(18) is 8.48(8) A.
The measurements of M€
ossbauer Spectra taken
without an external magnetic field consist of two
586
K.-L. Zhang et al. / Inorganic Chemistry Communications 7 (2004) 584–587
Fig. 3. 57 Fe Mossbauer spectra for the complex at 298 K (a) and
77 K (b).
Table 1
M€
ossbauer parameters for the complex
Temperature
(K)
Subspectrum
I.S.
(mm/s)
Q.S.
(mm/s)
Rel.
Int.(%)
298
The first doublet
The second doublet
0.25
0.23
0.70
0.46
49.2
50.8
77
The first doublet
The second doublet
0.38
0.37
0.85
0.49
49.5
50.5
measurements at 77 and 298 K (Fig. 3) [24]. Presumably
the rapid motion of the magnetic iron electronic moments causes the quenching of the magnetic hyperfine
structure, and both the spectra are doublets. It shows
that iron in this compound has two different chemical
environments. The observed values (Table 1) for the
isomer shift, I.S., range from 0.38 mm/s (a-Fe) at 77 K
to 0.25 mm/s at 298 K. The quadrupole splitting decreases with increasing temperature from 0.85 mm/s at
77 K to 0.70 mm/s at 298 K, values which are characteristic of high-spin iron(III) ions [25].
Acknowledgements
We gratefully acknowledge the National Natural
Science Foundation of China and the Nature Science
Foundation of Yangzhou University for the financial
support.
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[22] To a solution of trans-2-butenoic acid (2.724 g, 31.6 mmol) in
water (50 ml) was added a solution of NaOH (0.210 g, 5.2 mmol)
in water (5 ml). Then FeSO4 7H2 O (0.733 g, 2.6 mmol) was added
to the above solution and refluxed for 24 h. The brown crystals
were formed after several days (yield: 0.545 g). Anal. Calc. for
C68 H102 Fe6 O3 : C, 42.04; H, 5.29. Found: C, 42.42; H, 5.11.
[23] A
brown
crystal
having
approximate
dimensions
0.46 0.24 0.12 mm3 was used for data collection. Diffraction
data were collected with a Siemens P4 diffractometer using
graphite-monochromated (Mo KaÞ radiation (k ¼ 0:71073 A),
2h–h scan mode. The structure was solved by direct methods and
refined by a full-matrix least-squares on F2 method using the
SHELXL 97 program package. Complete listings of bond
distances and angles, hydrogen atoms coordinates and isotropic
displacement parameters, anisotropic displacement parameters
and least-squares plans are available quoting the deposition
number CCDC-203970 (12 Union Road, Cambridge, CB2 1EZ,
UK;
E-mail:
[email protected]).
Crystal
data:
C68 H102 Fe6 O43 , 1942.60 g mol1 , triclinic, P-1, a ¼ 14:724ð3Þ A,
b ¼ 17:818ð3Þ
A,
c ¼ 18:764ð5Þ
A,
a ¼ 103:200ð10Þ°,
3 , Z ¼ 2,
b ¼ 107:95ð2Þ°, c ¼ 92:010ð10Þ°, V ¼ 4529:8ð17Þ A
Dcalc ¼ 1:424 g cm3 , l(Mo KaÞ ¼ 1.024 mm1 , F ð0 0 0Þ ¼ 2020.
15,457 independent reflections were measured (Rint ¼ 0:0393). The
K.-L. Zhang et al. / Inorganic Chemistry Communications 7 (2004) 584–587
structure was refined to R1 ¼ 0:0516 (wR2 ¼ 0:1049) for the
reflections with I > 2rðIÞ (all data) and largest difference peak and
3 .
hole were 0.623 and )0.416 e A
[24] The M€
ossbauer experiments were carried out in zero applied
magnetic fields using a 57Co/Pd source and a constant acceleration spectrometer to collect the transmission spectra at 298 and
587
77 K (Fig. 3). The spectrometer was calibrated using a standard aFe foil. The isomer shifts are determined relative to the center of
the a-Fe spectrum. The MOSWIN program was used to determine
the M€
ossbauer parameters.
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