V-shaped Fe3III and linear FeII/Fe III/FeII complexes supported by phenyl-pyridine-2-yl- methanone oxime ligand: Solvothermal syntheses, structures and magnetic property

Article abstract of DOI:10.1016/j.inoche.2012.01.015

Under solvothermal conditions, one polynuclear Fe^III complex of formula [Fe₃{(py)C(ph)O}₄Cl₄][FeCl₄] (1) was synthesized from reaction of phenyl-pyridine-2-yl-methanone oxime (py)C(ph)NOH with FeCl₃, and one Fe^II/Fe ^III/Fe^II complex of composition [Fe₃{(py)C(ph) NO}₆][CH₃COO] (2) was prepared from treatment of (py)C(ph)NOH with Fe(OAc)₂. The most interesting synthetic feature of complex 1 is the in situ transformation of (py)C(ph)NOH into the (py)C(ph)O^- ligand. Complexes 1 and 2 were characterized by X-ray single crystal diffraction, IR spectroscopy, and elemental analysis. X-ray analysis revealed that complex 1 contains a V-shaped Fe^III core with two terminal Fe^III atoms displaying distorted square-pyramidal geometries and one central Fe^III ion exhibiting octahedron geometry. Complex 2 is a mixed-valence linear Fe^II/Fe^III/Fe ^II complex with all the three metal centers displaying distorted octahedron geometries. The low-temperature magnetic susceptibility measurement for the solid sample of 1 revealed the weak antiferromagnetic Fe ^III..Fe^III interactions. Theoretical calculations based on density functional theory were performed using the crystal structure of complex 1.

Full text of DOI:10.1016/j.inoche.2012.01.015

Inorganic Chemistry Communications 19 (2012) 4–9
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
V-shaped Fe3III and linear FeII/FeIII/FeII complexes supported by
phenyl-pyridine-2-yl-methanone oxime ligand: Solvothermal syntheses, structures
and magnetic property
a,c,
Wen-Qian Chen a, Yan-Mei Chen a, Tao Lei b, Wei Liu a, , Yahong Li
⁎
⁎
a
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, 215123, China
CAS Key Laboratory of Salt Lake Resources and Chemistry, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou, 730000, China
b
c
a r t i c l e i n f o
a b s t r a c t
Under solvothermal conditions, one polynuclear FeIII complex of formula [Fe3{(py)C(ph)O}4Cl4][FeCl4] (1)
was synthesized from reaction of phenyl-pyridine-2-yl-methanone oxime (py)C(ph)NOH with FeCl3, and
one FeII/FeIII/FeII complex of composition [Fe3{(py)C(ph)NO}6][CH3COO] (2) was prepared from treatment of
(py)C(ph)NOH with Fe(OAc)2. The most interesting synthetic feature of complex 1 is the in situ transformation
of (py)C(ph)NOH into the (py)C(ph)O− ligand. Complexes 1 and 2 were characterized by X-ray single
crystal diffraction, IR spectroscopy, and elemental analysis. X-ray analysis revealed that complex 1
contains a V-shaped FeIII core with two terminal FeIII atoms displaying distorted square-pyramidal
geometries and one central FeIII ion exhibiting octahedron geometry. Complex 2 is a mixed-valence linear
FeII/FeIII/FeII complex with all the three metal centers displaying distorted octahedron geometries. The
low-temperature magnetic susceptibility measurement for the solid sample of 1 revealed the weak anti-
ferromagnetic FeIII…FeIII interactions. Theoretical calculations based on density functional theory were
performed using the crystal structure of complex 1.
Article history:
Received 19 December 2011
Accepted 20 January 2012
Available online 28 January 2012
Keywords:
Crystal structures
Multinuclear iron complexes
Solvothermal synthesis
In situ reaction
Magnetic properties
© 2012 Elsevier B.V. All rights reserved.
Design and investigation of high-nuclearity paramagnetic transition
metal complexes with oxygen- and/or nitrogen based ligation continue
to attract intense attention [1], due to their potential applications as
functional materials, e.g., magnetic [2], optical [3], electronic [4] and cat-
alytic [5] etc., and their relevance to enzyme active centers in biological
systems [6]. The synthetic strategies for constructing these complexes
involve the continuous development of new synthetic methods, the
dexterous introduction of ancillary ligands, and the rational selection
of appropriate metal salts as the starting materials. Solvothermal tech-
nique has been proved as an effective synthetic method since past
decade, because solvothermal technique allows the application of high
temperatures to reactions in low or relatively low boiling solvents and
could directly generate pure, crystalline polynuclear products in good
yields. In situ metal/ligand reactions under solvothermal conditions
occur occasionally, which may result in the generation of novel coordi-
nation compounds exhibiting structural diversity and unique properties
[7]. The organic oximate compounds are fertile ligands for the prepara-
tion of 3d-metal clusters, since the oximate compounds possess the
bridging groups that can foster formation of polynuclear products. A
plenty of coordination compounds supported by the oximate ligands
with aesthetically pleasing structures and versatile magnetic properties
have been prepared [8].
We have been interested in synthesizing polynuclear complexes
by combining the above mentioned strategies. In the present work,
we have used (py)C(ph)NOH in combination with solvothermal
method for the synthesis of new multinuclear iron complexes. The
use of the anionic ligand (py)C(ph)NOˉ had previously given a pleth-
ora of MnIIMnIII [9], MnIIMnIV [10], CoIICoIII [11], CuII [12], NiII [13]
and ZnII [14] polynuclear compounds, but they were all synthesized
by “conventional” coordination chemistry techniques, i.e., solution
chemistry under atmospheric pressure and at temperatures limited
to the boiling points of common solvents. The coordination chemistry
of (py)C(ph)NOˉ with FeII and FeIII has been little explored, with only a
Fe2III complex [15] having been prepared by the conventional coordina-
tion chemistry techniques. We assume that there might be a number of
other high-nuclearity FeII or FeIII/(py)C(ph)NOˉ species available by
adopting solvothermal method, and we have now discovered a route
to the polynuclear [Fe3{(py)C(ph)O}4Cl4][FeCl4] (1) and [Fe3{(py)
C(ph)NO}6][CH3COO] (2) complexes. Herein, we report the syntheses,
structural characterizations of 1 and 2. The magnetic study of 1 was
also presented.
⁎
Corresponding authors at: Key Laboratory of Organic Synthesis of Jiangsu Province,
College of Chemistry, Chemical Engineering and Materials Science, Soochow Universi-
ty, Suzhou, 215123, China. Fax: +86 512 65880089.
Complexes 1 and 2 were prepared under solvothermal conditions
in EtOH. Treatment of FeCl3 with (py)C(ph)NOH in EtOH results in
E-mail address: liyahong@suda.edu.cn (Y. Li).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.01.015

W.-Q. Chen et al. / Inorganic Chemistry Communications 19 (2012) 4–9
5
Scheme 1. Synthesis of complex 1.
+
R
R
N
R
O
O
N
N
OH
N
N
N
-
O
N
EtOH,T,P
Fe
R
Fe
CH3COO
N
N
Fe
N
+
Fe(OAc)2
O
R
N
N
N
O
O
N
R
R
R = Ph
Scheme 2. Synthesis of complex 2.
the formation of 1 (Scheme 1). The most remarkable feature of this
reaction is the in situ formation of the (py)C(ph)O− ligand. The mech-
anism of the in situ formation of the (py)C(ph)O− ligand is unknown
now. It is proposed that the first step of this transformation involves
the hydrolysis of (py)C(ph)NOH to phenyl(pyridin-2-yl)methanone
((py)C(ph)=O) catalyzed by FeCl3 [16], which is a well-known
Lewis acid for accelerating the hydrolysis reaction, then the generated
phenyl(pyridin-2-yl)methanone was reduced to form the (py)C(ph)
O− ligand.
Treatment of Fe(OAc)2 with (py)C(ph)NOH in EtOH led to the
formation of 2 (Scheme 2). Apparently, reaction of the same li-
gand (py)C(ph)NOH with the different iron salts generated the
different complexes, demonstrating the synthetic novelty of this
work.
The molecular structures of complexes 1 and 2 are determined by
single crystal X-ray diffraction [17,18]. Complex 1 consists of a V-
–
shaped trinuclear cation [Fe3{(py)C(ph)O}4Cl4]+ and one [FeCl4] ion
for charge balance. Fig. 1 shows the cation structure of complex 1
with a labeling scheme. The coordination environments of the two ter-
minal FeIII atoms (Fe1 and Fe1′) are identical, and different from that of
the central FeIII atom (Fe2). The terminal Fe1(Fe1′) atom is coordinated
by two bridged deprotonated hydroxyl oxygen atoms originated from
two (py)C(ph)O− ligand, one nitrogen atom originated from one (py)
C(ph)O− ligand and two Cl− ions. The central FeIII atom is coordinated
by four bridged deprotonated hydroxide oxygen atoms originated from
four (py)C(ph)O− ligand, two nitrogen atoms originated from two (py)
C(ph)O− ligands.
The geometry around the central FeIII atom in the trimeric unit is best
described as a distorted octahedron having a N2O4 coordination environ-
ment, while the terminal two FeIII ions have square-pyramidal NO2Cl2
environments. The Fe3III cluster can be considered as an “inverted V
shape”, with Fe1 · · ·Fe2, Fe1′ · · · Fe2, and Fe1 · · · Fe1′ distances
being 3.15, 3.15, and 5.53 Å, respectively, and the metal–metal–metal
[Fe1-Fe2-Fe1′] bite angle being 122.59°. The {Fe1(μ-O)(μ-O)Fe2} motif
Fig. 1. (a) View of cation structure [Fe3{(py)C(ph)O}4Cl4] of 1, all H atoms are omitted
for clarity. (b) Coordination environments of the FeIII ions in 1.

6
W.-Q. Chen et al. / Inorganic Chemistry Communications 19 (2012) 4–9
Fig. 2. Crystal packing diagram of complex 1. Hydrogen contacts are represented by dotted lines.
Fig. 3. (a) View of cation structure [Fe3{(py)C(ph)NO}6]+ of 2, all H atoms are omitted for clarity. (b) Coordination environments of the metal ions in 2.

W.-Q. Chen et al. / Inorganic Chemistry Communications 19 (2012) 4–9
7
Fig. 4. Crystal packing in complex 2. The π…π stacking interaction is indicated by dotted lines.
is asymmetrical, with Fe1–O1, Fe2–O1, Fe1–O2, and Fe2–O2 bond dis-
tances being 1.967(3), 1.986(3), 1.992(3), and 1.969(3) Å, respectively.
As shown in Fig. 2, complex 1 features intramolecular C-H…Cl hydrogen
contacts between CH group of phenyl ring as hydrogen atom donor and
geometries, with the six sites on each Fe ion is occupied by the nitrogen
atoms of three (py)C(ph)NO− ligands.
Charge considerations indicate that two Fe ions of 2 are in 2+
valence states and the central Fe ion is in 3+ valence state [19]. The ter-
minal metal ions are clearly low-spin FeII ions based on their Fe–N bond
lengths (all b1.96 Å), which are similar to FeII–N bond lengths in other
structurally characterized FeII complexes with N-ligation. The central
iron atom has all six Fe–O distances of 2.018–2.036 Å indicating its 3+
valence state. Each ligand chelates one FeII ion through the 2-pyridyl
and the oximate nitrogen atoms forming a five-membered chelat-
ing ring, and bridges this metal center with the central FeIII ion
through the terminally ligated, deprotonated oxygen atom. Strong
π…π stacking interactions with a centroid-to-centroid distance be-
tween pyridyl-rings of 3.57 Å are observed in the crystal, forming
a “dimmer” structure (Fig. 4).
–
chloride atom from [FeCl4] anion as acceptor (C15-H15…Cl6, C to
Cl distance 3.449(7) Å, C15-H15…Cl6 angle 128°, symmetry operation
1−x, 1+y, 1/2−z). In addition, noticeable intermolecular C-H…Cl con-
tacts (C18-H18…Cl2, C to Cl distance 3.429(4) Å, C18-H18…Cl2 angle
127°, symmetry operation 1/2−x, −1/2+y, 1/2−z) are presented
from CH group of the pyridyl-ring (donor) to the coordinated chloride
atom (acceptor). These hydrogen contacts connect the molecules to
generate infinite 2D network.
The X-ray single crystal determination reveals that complex 2 con-
sists of a linear trinuclear cation, and one CH3COO− ion to compensate
the positive charge of the cation. As shown in Fig. 3, the central metal
ion, Fe3, which is located on a crystallographic inversion centre, is octa-
hedrally coordinated by six oxygen atoms which belong to six (py)
C(ph)NO− ligands. The two terminal FeIII ions also adopt octahedral
Magnetic property studies on polynuclear metal complexes are of
continuing interest for coordination chemists since they can provide
the understanding of fundamental factors governing their magnetic
13
12
11
10
30
9
25
8
20
7
15
10
6
5
5
0
0
50
100
150
T / K
200
250
300
4
0
50
100
150
200
250
300
T/ K
Fig. 5. Temperature dependence of magnetic susceptibilities in the form of χMT vs T for 1 at 1 kOe. Inset: Temperature dependence of magnetic susceptibilities in the form of χM−1 vs
T for 1 at 1 kOe. The solid line corresponds to the best fit from 150 K to 2 K.

8
W.-Q. Chen et al. / Inorganic Chemistry Communications 19 (2012) 4–9
Table 1
terminal Cl anions, which could be considered as reasonable in
a “V-shaped” environment. In addition, the magnetic exchange path-
way is primarily mediated by the bridging μ3-O atoms from (py)C(ph)
NOH ligands, and these mediators support an antiferromagnetic
interaction.
Selected experimental and calculated bond lengths/A˚ and angles/ for complex 1.
Exptl.
Calcd.
Fe1-O1
Fe1-O2
Fe2-O1
Fe2-O2
1.967(3)
1.992(3)
1.986(3)
1.969(3)
122.59
1.990
2.030
2.026
1.989
126.85
In summary, two polynuclear iron complexes of the compositions
[Fe3{(py)C(ph)O}4Cl4][FeCl4] (1) and {[Fe3{(py)C(ph)NO}6][CH3COO]
(2) have been synthesized by solvothermal reaction, and character-
ized by X-ray single crystal diffraction, IR spectroscopy, and elemental
analysis. The (py)C(ph)O− ligand of complex 1 was formed by the
FeCl3 catalyzed in situ metal ligand reaction. The work described
above also demonstrates the synthetic novelty that arises when sol-
vothermal techniques are used in FeII/2-pyridyl oxime chemistry.
Magnetic property measurement indicates that there exist weak anti-
ferromagnetic interactions between the magnetic centers in 1.
Magneto-structural correlation was investigated by theoretical calcu-
lations, which suggested the observed magnetic behaviors were due
to the μ3-O atoms from (py)C(ph)NOH ligands in the bridging path-
way. These results indicate that the phenyl-pyridine-2-yl-methanone
oxime ligand is a useful linkage for the synthesis and design of new
functional materials.
Fe1-Fe2-Fe1′
properties. The dc magnetic property for 1 was measured in the tem-
perature range of 2–300 K at the applied magnetic field of 1000 Oe.
The obtained data are shown in Fig. 5 in the χMT vs T and χM−1 v T
forms.
The χMT value is 11.94 cm3 mol−1 K at 300 K, slightly smaller than
the spin-only value (13.13 cm3 mol−1 K) expected for three magneti-
cally isolated high-spin FeIII ions (S=5/2, g=2.00), indicating the
presence of weak antiferromagnetic interactions. Upon cooling, χMT
value decreases gradually and reaches to 8.19 cm3 mol−1 K at 35 K,
and then decreases steeply to 4.68 cm3 mol−1 K at 2 K.
The magnetic properties were tried to be analyzed by the Hamiltonian
E(ST,S23)=−J[ST(ST+1)−S23(S23 +1)] [20], but no reasonable parame-
ters were obtained. The magnetic data of χM−1 v T from 2 to 150 K (linear
part) was then fitted by the Curie–Weiss law.
Acknowledgements
The Curie–Weiss fitting of the magnetic data yields
C=9.04 cm3 mol−1 K and θ=−2.57 K, indicating the presence
of weak antiferromagnetic exchange coupling interactions among
the metal centers.
To gain insight into the magnetic exchange mechanism, complex 1
was selected for representative DFT calculations [21]. The cation
geometry of the crystal structure was fully optimized (B3LYP func-
tional [22]; 6–31 G* basis set for C, H, N, O, and Cl atoms; effective
core potentials (LANL2DZ) for Fe atoms; gas phase). The DFT calculat-
ed bond lengths and angles of 1 agree sufficiently well with the
experimentally observed ones (Table 1).
The authors appreciate the financial supports of Hundreds of Talents
Program (2005012) of CAS, Natural Science Foundation of China
(20872105), “Qinglan Project” of Jiangsu Province (Bu109805) and A
Project Funded by the Priority Academic Program Development of Jiangsu
Higher Education Institutions.
Appendix A. Supplementary material
CCDC 841776 and 848421contain the supplementary crystallo-
graphic data for complexes 1 and 2. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
to this article can be found online at doi:10.1016/j.inoche.2012.01.
015.
The spin density distributions for the high-spin state (16-et, S=5/
2 for each FeIII ion) are illustrated in Fig. 6. It can be seen that, the spin
density is localized mainly on the three iron(III) centers and four
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=
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=
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