A unique 2D framework containing linear trimeric cobalt(ii) of mixed T d-Oh-Td geometries linked by two different single-carboxylate-aromatic amine ligands: Structure and magnetic properties

Article abstract of DOI:10.1039/b718928a

A new 2D coordination polymer Co₃(OH)₂(pa) ₂(ina)₂ (1, pa = 3-(1H-benzimidazol-2-yl) propanoic carboxylate, ina = isonicotinate) contained uncommon, linear Co(ii) trimers of mixed T_d-O_h-T_d geometries, exhibits spin canting below 20 K. Such magnetic behavior mainly arises from the Dzyaloshinski-Moriya interaction from the anisotropic, mixed geometries trimeric Co(ii) ions to the crimpled 2D network based on the nature of the binding modes of Co(ii)-carboxylate trimer and the effect of the intertrimers arrangement of 1. The mixed single-carboxylate-aromatic amine ligands bridged metal systems display a new structurally authenticated example of a thick 2D layer, and also indicate homometallic Co(ii) clusters with T_d-O_h-T _d mixed-geometries can result in relatively obvious noncompensation moments, according to different efficient spins of Co(ii) at very low temperature, in spite of antiferromagnetic intracluster interactions. The Royal Society of Chemistry.

Full text of DOI:10.1039/b718928a

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A unique 2D framework containing linear trimeric cobalt(II) of mixed
T –O –T geometries linked by two different single-carboxylate-aromatic
d
h
d
amine ligands: structure and magnetic properties†
a
a,b
a
a
a
Min-Xia Yao, Ming-Hua Zeng,* Hua-Hong Zou, Yan-Ling Zhou and Hong Liang*
Received 7th December 2007, Accepted 21st February 2008
First published as an Advance Article on the web 20th March 2008
DOI: 10.1039/b718928a
A new 2D coordination polymer Co
carboxylate, ina = isonicotinate) contained uncommon, linear Co(II) trimers of mixed T
geometries, exhibits spin canting below 20 K. Such magnetic behavior mainly arises from the
3
(OH)
2
(pa)
2
(ina)
2
(1, pa = 3-(1H-benzimidazol-2-yl) propanoic
d
–O –T
h
d
Dzyaloshinski–Moriya interaction from the anisotropic, mixed geometries trimeric Co(II) ions to the
crimpled 2D network based on the nature of the binding modes of Co(II)-carboxylate trimer and the
effect of the intertrimers arrangement of 1. The mixed single-carboxylate-aromatic amine ligands
bridged metal systems display a new structurally authenticated example of a thick 2D layer, and also
indicate homometallic Co(II) clusters with T
d
–O
h
–T mixed-geometries can result in relatively obvious
d
noncompensation moments, according to different efficient spins of Co(II) at very low temperature, in
spite of antiferromagnetic intracluster interactions.
Introduction
lattices, which is beneficial both in single molecule magnets and
model compounds for the study of low-dimensional magnetism.
7
The carboxylate unit is widely used in the synthesis of coordination
In our course of ongoing studies on transitional metal com-
1
polymers; for the dicarboxylate entity in particular, and a plethora
5a,b
plexes of carboxylate-aromatic amine ligands,
we introduced
of studies has detailed the synthesis of metal dicarboxylates that
exhibit useful properties such as high porosity and magnetism.
Research has also been extended to include other ligands into
the metal dicarboxylate system, and a commonly used ligand
rigid ina and flexible pa ligands in the preparation of the new mag-
netic molecular construction. The different coordination modes
adopted by the different carboxylate groups perform the trans-
mission of the magnetic coupling to different degrees and through
the heteroatomic coordination of the linkers may result in the
extension of frameworks. Herein, we report the synthesis, structure
2
,3
4
5
is the pyridyl-type of spacer heterocycles. The research of
metal monocarboxylate systems are few in comparison with the
1
above studies. Commonly, it is difficult for two different kinds
and magnetic properties of a 2D complex Co
constructed from two different kinds of monocarboxylate ligands
pa and ina) featuring mixed hydroxyl/carboxylate-bridged linear
3
(OH)
2
(pa)
2
(ina)
2
(1)
of negative monocarboxylate ligands to coexist in the same
molecule because of their competition in the process of self-
(
1
assembly. The carboxylates are capable of not only transmitting
trinuclear Co(II) clusters as subunits.
magnetic exchanges and binding to metal clusters or chains,
but also can stretch the metal building units into aesthetically
pleasing frameworks.
1–3
Experimental
Accordingly, many antiferromagnetic,
ferromagnetic and metamagnetic materials have been prepared
Materials and measurements
1,3a,5
using carboxylates as functional groups.
Magnetic metal
complexes constructed by monocarboxylate ligands may favor
low-dimensional structures exhibiting distinctive properties, such
as slow relaxation, and spin glasses are important in the fields of
quantum mechanics and experimental and theoretical solid-state
science. The formation of new magnetic materials with the pres-
ence of high-anisotropy magnetic clusters isolated within extended
All the starting chemicals were of AR grade and used as received
while Hpa was synthesized according to a literature procedure (see
ESI†).
6
Co
reaction mixture of Co(NO
HL (0.5 mmol), NaOH (1 mmol), triethylamine (0.1 mL) and
O (10 mL) in a Teflon-lined autoclave under autogenous
3
(OH)
2
(pa)
2
(ina)
2
(1). This complex was synthesized from a
3
)
2
·6H O (0.75 mmol), Hpa (0.5 mmol),
2
H
2
pressure at 423 K for 105 h. Then dark-purple block crystals
were obtained and picked out, washed with distilled water and
dried in air. Yield: 32% (based on Co(II)). Anal. Calc. (%) for
C H Co N O : C, 46.12; H, 3.39; N, 10.08. Found C, 45.89; H,
a
Key Laboratory of Medicinal Chemical Resources and Molecular Engineer-
ing, GuangXi Normal University, Guilin, 541004, P. R. China
b
State Key Laboratory of Optoelectronic Materials and Technologies, Sun
Yat-Sen University, Guangzhou, 510275, P. R. China. E-mail: zmh@
mailbox.gxnu.edu.cn; Fax: +86 773 5812-383
3
2
28
3
6
10
−1
3
1
.30; N, 10.15%. IR data for 1 (KBr, cm ): 3428w, 3160m, 1673s,
579m, 1523s, 1495s, 1461s, 1298m. Elemental analyses (C, H, N)
†
Electronic supplementary information (ESI) available: Additional figures
and an X-ray crystallographic file for the structure determination of 1.
CCDC reference number 669902. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b718928a
were performed on an Elementar Vario EL analyzer. IR spectra
were recorded on a Nicolet Magna-IR 750 spectrometer equipped
2
428 | Dalton Trans., 2008, 2428–2432
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with a Nic-Plan Microscope. Temperature- and field-dependent
magnetic measurements were carried out on a SQUID-MPMS-XL
magnetometer. Diamagnetic corrections were made with Pascal’s
constants. X-Ray powder diffraction data were collected on a
Rigaku D/max-IIIA powder X-ray diffractometer.
Results and discussion
Crystal structures
Single-crystal X-ray diffraction shows that 1 consists of a two-
dimensionalcovalent networkconstructedbylinear trimericCo(II)
ions subunits (Fig. 1). The central Co(1) atom, being located at a
crystallographic inversion centre, is coordinated by two l-hydroxyl
X-Ray crystallography
˚
(
Co(1)–O(1) 2.003(2) A), two trans-related nitrogen atoms (Co(1)–
˚
N(3b) 2.202(3) A) from ina groups and two carboxyl oxygen
Diffraction data were collected on a Bruker Smart Apex CCD
diffractometer with graphite monochromated Mo-Ka radiation
˚
atoms (Co(1)–O(2) 2.141(2) A) from pa groups, with a distorted
octahedral geometry. Each of the two terminal Co(II) atoms has a
tetrahedral coordination environment, by a l-hydroxyl (Co(2)–
˚
(
k = 0.71073 A) at room temperature, and absorption corrections
8
were applied by SADABS. The structures were solved by direct
methods and refined using full-matrix least-squares technique
with SHELXL-97. All non-hydrogen atoms were refined with
˚
O(1) 1.888(2) A), a nitrogen and oxygen atom (Co(2)–N(1d)
8
2.042(2) A˚ ) from two pa ligands, and an oxygen atom (Co(2)–
˚
O(4) 1.977(2) A) from an ina ligand. The central Co(II) atom is
anisotropic displacement parameters, while all hydrogen atoms of
the ligands were placed at idealized positions and refined as riding
atoms. Experimental details of the X-ray analyses are provided
in Table 1 while selected bond distances and angles are listed in
Table 2.
CCDC reference number 669902.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b718928a
linked to each terminal Co(II) atom by l-hydroxyl and a syn-syn
˚
l-1,3-carboxylate mixed bridge (Co · · · Co 3.375(1) A, Co–O–Co
◦
1
20.2(1) ) to form linear trimeric Co(II). In contrast, the metal cen-
ters usually have the same octahedral geometries in documented
II
linear trinuclear M , and containing mixed azide and carboxylate
9
bridges complex. Further, such reported cobalt complexes have a
linear trinuclear mode with O
h
–T
d
–O
h
or O
h
–O
h
–O geometry, and
h
are always interlinked with each other through corner-sharing or
edge-sharing exhibiting chain or layer structures within the metal
10
Table 1 Crystallographic data and structure refinement for 1
organic frameworks, and in compound Co(H O) (C H O ), the
2
2
4
4
4
metal centers formed isolated linear trinuclear clusters within a
Formula
C
833.41
Triclinic
P1
8.209(4)
10.023(4)
10.459(5)
89.260(8)
87.753(8)
68.912(7)
802.3(6)
1
32
H
28Co
3
N
6
O
10
10e
chain structure showing O
kind of tridentate-N,O,O mode (Fig. 2), utilising two carboxy
h
geometry. The pa ligands act in a
M
r
ꢀ
Crystal system
¯
oxygen atoms (syn-syn) to bridge one O and one T cobalt atoms
Space group
h
d
a/A˚
and the imidazole nitrogen atom to link a same side T cobalt atom
d
b/A˚
c/A˚
in adjacent trinuclear units to form 1D molecular ladders with
˚
the thickness of ca. 11 A (C · · · N distance). The more important
◦
a/
b/
◦
feature is that infinite molecular ladders are formed in which the
metal trimeric entities are linked to each other along a flexible
linear ligands and these ladders involve large 18-membered-ring
structures in their backbones and further interlinked on each other
◦
c /
V/A˚
3
Z
−
3
D
c
/g cm
1.725
1.603
273(2)
−
1
l/cm
T/K
Independent reflections
No. observations
R (I > 2r(I))
3455 (Rint = 0.074)
6823
0.0371
0.085
wR (all data)
◦
Table 2 Selected bond lengths ( A˚ ) and angles ( ) for 1
Co(1)–O(1)
Co(1)–O(2)
Co(1)–N(3b)
Co(2)–O(1)
Co(2)–N(1d)
2.005(2)
2.141(2)
2.202(3)
1.890(2)
2.043(2)
Co(1)–O(1a)
Co(1)–O(2a)
Co(1)–N(3c)
Co(2)–O(4)
Co(2)-O(3)
2.005(2)
2.141(2)
2.202(3)
1.977(2)
2.057(2)
O(1)–Co(1)–O(2)
O(1a)–Co(1)–O(2)
O(1a)–Co(1)–N(3b)
O(2a)–Co(1)–N(3b)
N(3b)–Co(1)–N(3c)
O(4)–Co(2)–N(1d)
O(4)–Co(2)–O(3)
92.75(8)
87.25(8)
90.44(9)
91.22(9)
180.00
118.34(1)
93.92(1)
O(1)–Co(1)–O(2a)
O(1a)–Co(1)–O(2a)
O(1)–Co(1)–N(3b)
O(2)–Co(1)–N(3b)
O(1)–Co(2)–O(4)
O(1)–Co(2)–O(3)
87.25(8)
92.75(8)
89.56(9)
88.78(9)
123.99(1)
103.90(1)
Symmetry transformations used to generate equivalent atoms: (a) −x + 1,
y, −z; (b) −x + 2, −y − 1, −z; (c) x − 1, y + 1, z; (d) x + 1, y, z.
−
Fig. 1 The Co(II) coordination environments in the trinuclear unit of 1.
Dalton Trans., 2008, 2428–2432 | 2429
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Fig. 2 Perspective view of infinite ladder in 1 made up of trimeric Co(II)
subunits linked by pa ligands along the b axis (top) and infinite chain
of trimeric Co(II) subunits linked by l-ina-N,O ligands along the c axis
(
bottom).
by two l-ina-N,O ligands with opposite directions into a 2D layer
(
9
Fig. 3 and Fig. S1, ESI†) with an interladder separation of ca.
˚
.1 A (Co · · · Co distance). The hydroxyl ligands in the ladder
˚
show a interlayer hydrogen bonding (O(1) · · · O(5) 3.084(2) A)
Fig. 4 Perspective views of the 3D packing of 1 along the a axis.
to uncoordinated carboxylate oxygens of ina linkers. The strong
˚
−1
hydrogen bonds (N(2) · · · O(3) 2.770(2) A) between the nitrogen
temperature v
temperature, v
m
T value of 7.45 emu K mol . Upon lowering the
atoms of benzimidazole and coordinated carboxylate oxygens
of the pa linkers in the adjacent lamellar tightly hold together
m
T decreases, reaches a small shoulder at 20–15 K,
−1
and then rapidly decreases to a minimum of 2.39 emu K mol
at 2 K (Fig. 5). The molar magnetic susceptibility per Co
in the temperature range 70–300 K obeys the Curie–Weiss law
Co
3
(OH)
2
(pa)
2
(ina)
2
layers, leading to a 3D structure, where the
˚
3
unit
shortest Co · · · Co interlayer separation is 7.75 A (Fig. 4).
3
−1
[
v
m
= C/(T − h)], i.e., C = 8.78 cm mol K and h = −48.5(1)
K, consistent with the presence of three Co(II) ions. Furthermore,
the large negative h value suggests a dominant antiferromagnetic
coupling between Co(II) ions within the trimeric entity; and the
single-ion behavior of octahedral Co(II) contributes somewhat to
the h value. The field-dependence of v T vs. T shows that the
m
maximum at low temperatures decreases with increasing applied
field at 20 K (Fig. 5 inset), which is an indication of the source
5c,d
of an obvious spontaneous moment is probably spin canting.
Indeed, the AC magnetic susceptibility data confirm the presence
ꢀꢀ
of net magnetization as the data show a peak in the v
m
(out-
of-phase) signals below 20 K (Fig. S2, ESI†). The position of
the maxima shows very slight frequency dependence within the
Fig. 3 The 2D framework of 1 viewed along the b-axis. The aromatic
rings of pa and hydrogen atoms are omitted for clarity.
So far few mixed hydroxyl/carboxylate-bridged linear trinuclear
9
Co(II) complex of mixed geometries have been documented; in
contrast, carboxylate-bridged ‘paddlewheel’ dinuclear and ‘basic
triangular’ trinuclear metal complexes have been widely inves-
1–3
tigated and often show antiferromagnetic interactions. These
species, which are analogous to complex 1, are crucial for in-
creasing our understanding of bonding and magnetic interactions
between proximate metal centers. Meanwhile, open-framework
metal complexes containing linear trinuclear metal subunits could
lead to new magnetic behavior induced by the intrinsic properties
of these noncompensated magnetic units arising from ferromag-
netic coupling or antiferromagnetic coupling, and further may
lead to the generation of more interesting magnetic properties as
well as to a better understanding of cooperative effects of magnetic
5
,6
clusters within the framework motif.
Fig. 5 Temperature dependence of the magnetic susceptibility of 1
measured at 10 kOe. The solid line represents the best fit given in the
text. Inset the plot of vT vs. T under different field at low temperature.
Magnetic susceptibility measurements carried out on crushed
single crystals of 1 with an applied field of 10 kOe revealed a room-
2
430 | Dalton Trans., 2008, 2428–2432
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1
1
range 1–997 Hz that is indicative of a spin canting behavior.
magnitude of the coupling constants in the 2D networks of 1
5a,d
this is also consistent with the presence of the bifurcation point
cannot be calculated by conventional methods.
To evaluate
between the field-cooled/zero-field-cooled magnetization curves
the interactions, with the molecular field approximation, and
an admittedly simple model, a least-squares fit of the observed
magnetic data based on the theoretical expression of a trimer with
antiferromagnetic interactions was made (eqn (1), Fig. 5 inset).
The Hamiltonian for the linear trimer in 1 is given by eqn (1):
ꢀ
below 20 K (Fig. 6). At very low temperatures v
m
and FC/ZFC
curves undergo a slight increase which could be because of the
presence of a paramagnetic contribution arising from defects in
10b
the crystal structure. Plots of M vs. H at temperatures above
and below the transition temperature are shown in the inset of
Fig. 6. The shapes of the M/H plots are quite like those of a
ˆ
H
ˆ ˆ
ex = −2J(S
ˆ ˆ
+ S
1
S
2
2
S
3
)
(1)
12
recently reported canted-spin antiferromagnet, in which the M
values increase approximately linearly with H, do not saturate. At
ꢀ
ꢀ
ꢀ
Then, E(S ,S13) = −J(S (S + 1) −S13(S13 + 1) −S
2
(S
2
+ 1)) where
;Sꢀ
S
13 = S
1
+ S
3
3
= S13 + S
2
:
2
K, the saturation magnetization in a field of 70 kOe is 3.89 l
B
per Co formula unit. For octahedral Co(II), the effect of spin–
3
(
(
2)
3)
orbit coupling is usually to yield a Kramers S = 1/2 state at low
temperature with an anisotropic g-tensor and a moment of 2.2
11,13
l
B
per Co(II).
As such, the observed saturation moments for
the Co unit are nearly equivalent to the resultant moment of one
3
CoOct [assuming an effective S = 1/2, and two CoTd, assuming
an effective S = 3/2 at low temperatures]. The ferrimagnetic-
like cluster configurations necessary to give this total moment is
one octahedral site (↓) that is antiferromagnetically coupled to
two tetrahedral sites (↑↑↑). However, isothermal magnetization
measurements show no detectable hysteresis loop (Fig, S3, ESI†).
where, J is the intra-trimer exchange interaction through mixed
ꢀ
ꢀ
l-hydroxyl and l-carboxylate-O,O groups, J is the inter-trimer
exchange interaction and z is the number of nearest neighbors of
ꢀ
the trimer. By varying g, J, J and minimizing the residual R =
ꢀ
ꢀ
ꢀ
ꢀ
2
2
2
2
[
(vobsT − vcalcT) / (vobsT) ] or R = [ (vobs − vcalc) / (vobs) ],
the best non-linear least-squares fittings of the theoretical and
expression to the experimental data can be made. The model
provides a proper fit of v /T variation over the temperature
m
range 50–300 K, with a discrepancy that does not exceed the
experimental uncertainty. The closest agreement between theory
and experiment, comes from use of the following parameter values:
−
1
ꢀ
−1
g = 2.37, J
1
= −5.09 cm , and zJ = −0.009 cm R = 2.7 ×
−
4
−1
ꢀ
10
for plot of v
m
vs. T, and g = 2.41, J
1
= −5.73 cm , zJ =
−
1
−4
−
0.006 cm , R = 1.7 × 10 for plot of v
m
T vs. T. The J value
1
is comparable to those previously reported for Co(II) complexes
5c,12,14
ꢀ
with similar bridges,
and the J value confirms very weak
mediators of r-bonding ditopic linkers among the trimers within
the layer.
Why does the Co(II) system show a canting phenomenon?
Usually, there are two mechanisms by which weak ferromagnetism
11
(
canting) may occur. One is single-ion anisotropy, which results
in a zero-field splitting, and the other is antisymmetric spin–spin
coupling, an extra-term in the spin Hamiltonian that usually
is taken as isotropic. The antisymmetric exchange is termed as
the Dzyaloshinski–Moriya interaction (D–M interaction) and
cants the spins. From the structural point of view, there are
two crystallographically independent Co(II) ions, with mixed
geometry trimers bridged by mixed l-hydroxyl and l-carboxylate-
Fig. 6 Field-cooled and zero-field-cooled magnetization curves. Inset
magnetization isotherms for 1 measured at 2, 5, 10, 15 and 30 K.
The structure of 1 is complex, a fact that leads to questions
about the exact dimensionality of the magnetic interactions in this
system. The above data do not allow for a precise understanding
of the nature of the magnetic ordering. The dipolar coupling
between the clusters mediated by ina and pa ligands may be
ꢀ
ꢀ
O,O groups, which are linked by l-ina-N,O and l
3
-pa-N,O,O
ligands into a nonplanar 2D network (Scheme 1) in 1, and D–M
12
5a,d
antiferromagnetic and weak. Superexchange within the trimers
is expected to be stronger than the dipolar coupling between
these features so that long-range ordering will be diminished.
The interlayer interaction is also a dipolar one across a relatively
interaction may be the first key to the canting behavior.
On
the other hand, there is the consequence of the strong magnetic
anisotropy of the Co(II) ions, with moderate spin–orbit coupling
4
[from its T1g ground state], in conjunction with spin canting within
˚
large gap of approximately 8 A; it is small and only becomes
the layers. Although the ina and pa bridges do not likely have any
12
significant at very low temperatures, the bulk magnetic behavior
of 1 is consistent with the cooperation of the trimers in the 2D
importance in terms of the long-range order, the interactions are
also probably modulated by the flexible/rigid organic bridges that
enhance the magnetic inter-cluster interactions in 2D framework
and lead to cooperative magnetic behavior, since the through-space
separation of the trimers is very different from that of discrete
5a,b
framework.
Zero-field splitting, and the more common complications aris-
ing from spin–orbital interactions, is a frequent source of difficulty
in the interpretation of magnetic data for Co(II) complexes. The
13
5,15
molecular trimer systems.
This journal is © The Royal Society of Chemistry 2008
Dalton Trans., 2008, 2428–2432 | 2431

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4
5
B. H. Ye, M. L. Tong and X. M. Chen, Coord. Chem. Rev., 2005, 249,
5
45.
(a) M. H. Zeng, M. C. Wu, H. Liang, Y. L. Zhou, X. M. Chen and
S. W. Ng, Inorg. Chem., 2007, 46, 7241; (b) H. J. Chen, Z. W. Mao, S.
Gao and X. M. Chen, Chem. Commun., 2001, 2320; (c) M. H. Zeng,
X. L. Feng, W. X. Zhang and X. M. Chen, Dalton Trans., 2006, 5294;
(
d) M. H. Zeng, B. Wang, X. Y. Wang, W. X. Zhang, X. M. Chen and S.
Gao, Inorg. Chem., 2006, 45, 7069; (e) M. H. Zeng, W. X. Zhang, X. Z.
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6
7
(a) L. Lecren, O. Roubeau, C. Coulon, Y. G. Li, X. L. Goff, W.
Wernsdorfer, H. Miyasaka and R. Cl e´ rac, J. Am. Chem. Soc., 2005,
Scheme 1 Chart of the superexchange-mediated 2D lattice in 1. Red
lines: two alkoxo bridges; pink lines: triple bridge through pa; blue lines:
ina bridge.
1
27, 17353; (b) H. Miyasaka, K. Nakata, L. Lecren, C. Coulon, Y.
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(
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Conclusions
8
9
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In summary, this work presents a new synthetic strategy for
building magnetic coordination polymers by using differently
flexible and rigid single-carboxylate-aromatic amine ligands. The
(a) F. P. W. Agterberg, H. A. J. P. Kluit, W. L. Driessen, H. Oevering,
W. Buijs, M. T. Lakin, A. L. Spek and J. Reedijk, Inorg. Chem., 1997,
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Ed., 2007, 46, 6076; (c) P. K. Chen, Y. X. Che, J. M. Zheng and S. R.
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antisymmetrical, antiferromagnetic correlation of anisotropic Co
3
clusters leads to a weak ferromagnetic behavior below 20 K, this
is essentially due to increasing of structural dimensionality from
isolated clusters to a 2D layer, from the nature of the different
11
binding modes of short and long bridges. Our results also
support, in spite of showing antiferromagnetic interaction within
1
0 (a) C. Rodolphe, F. A. Cotton, R. D. Kim, T. B. Lu, A. M. Carlos
and X. P. Wang, J. Am. Chem. Soc., 2000, 122, 2272; (b) J. R. Gal a´ n-
Mascar o´ s and K. R. Dunbar, Angew. Chem., Int. Ed., 2003, 42, 2289;
(c) S. O. H. Gutschke, D. J. Price, A. K. Powell and P. T. Wood, Angew.
Chem., Int. Ed., 2001, 40, 1920; (d) A. Rujiwatra, C. J. Kepert, J. B.
Claridge, M. J. Rosseinsky, H. Kumagai and M. Kurmoo, J. Am. Chem.
Soc., 2001, 123, 10584; (e) P. M. Forster, A. R. Burbank, C. Livage, G.
F e´ rey and A. K. Cheetham, Chem. Commun., 2004, 368.
the cluster, the T
d
–O
h
–T mixed-geometries-based Co(II) cluster
d
can result in relatively effective noncompensation moments at very
low temperature. Increasing of structural dimensionality from the
isolated cluster to a 2D framework provides a unique opportunity
to investigate new and cooperative magnetic behaviors and also
15
the frontier between magnetic cluster and classical bulk magnets.
1
1
1 (a) O. Kahn, Molecular Magnetism, VCH Publishers, New York, 1993,
3
22; (b) From the Molecular to the Nanoscale: Synthesis, Structure,
Acknowledgements
and Properties, ed. M. Fujita, A. Powell and C. Creutz, Elsevier-Ltd.,
Oxford, 2004, vol. 7.
This work was supported by NSFC (No. 20561001), the Program
for New Century Excellent Talents in University of the Ministry
of Education China (NCET-07-0217), GKN (Grant 0630006-
2 (a) F. C. Liu, Y. F. Zeng, J. Jiao, X. H. Bu, H. J. Zhang, J. Ribas and
S. R. Batten, Inorg. Chem., 2006, 45, 2776; (b) J. R. Li, Q. Yu, Y. Tao,
X. H. Bu, J. Ribas and S. R. Batten, Chem. Commun., 2007, 2290;
(
c) Y. F. Zeng, F. C. Liu, J. P. Zhao, S. Cai, X. H. Bu and J. Ribas,
5
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D), and GJY (Grant 2006-26) as well as IPGGE (Grant
006106020703M34).
Chem. Commun., 2006, 2227.
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Angew. Chem., Int. Ed., 2007, 46, 1832; (b) W. E. Hatfield, in Magneto-
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D. Gatteschi and O. Kahn, Reidel, Dordrecht, The Netherlands, 1984.
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432 | Dalton Trans., 2008, 2428–2432
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