Two cobalt(II) 5-aminoisophthalate complexes and their stable supramolecular microporous frameworks

Article abstract of DOI:10.1021/ic0602244

Two stable supramolecular microporous cobalt(II) polymers, namely [Co(HAIP)₂]_n?3nH₂O (1) and [Co(AIP)(H ₂O)]_n (2), AIP = 5-aminoisophthalate, were hydrothermally synthesized and characterized by single-crystal X-ray diffraction, IR spectra, thermogravimetric analyses, and variable-temperature magnetic susceptibility measurements. The two complexes are constructed from the same Co ₂(CO₂)₂ SBU, which is extended into a 1D chain in 1 and a 2D layer in 2. As a result, 1 and 2 are 2D and 3D coordination polymers, respectively. The 3D supramolecular network of complex 1 is held up by strong hydrogen bonds formed between carboxylate groups and shows very high stability when the free H₂O molecules are removed, indicating an extraordinarily stable H-bonding system. Upon water ligands being liberated, complex 2 becomes a stable microporous solid with coordination-unsaturated Co centers. The behavior of the susceptibility curve of 1 suggests the occurrence of an interesting intrachain antiferromagnetic coupling between the Co(II) ions and the presence of a significant orbital contribution, whereas the features of 2 indicate an antiferromagnetic coupling with T_N = 3.5 K and a long-range antiferromagnetic order with a field-induced magnetic transition.

Full text of DOI:10.1021/ic0602244

Inorg. Chem. 2006, 45, 6276−6281
Two Cobalt(II) 5-Aminoisophthalate Complexes and Their Stable
Supramolecular Microporous Frameworks
En Tang,† Yu-Mei Dai,†,‡ Jian Zhang,† Zhao-Ji Li,† Yuan-Gen Yao,*,† Jie Zhang,*,† and Xu-Dong Huang§
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of
Matter, The Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China, College of
Chemistry & Material Science, Fujian Normal UniVersity, Fuzhou, Fujian 350007, P. R. China,
and Genetics & Aging Research Unit, Massachusetts Institute of NeurodegeneratiVe Diseases and
Department of Psychiatry, Massachusetts General Hospital and HarVard Medical School,
Charlestown, Massachusetts 02129
Received February 9, 2006
Two stable supramolecular microporous cobalt(II) polymers, namely [Co(HAIP)
2), AIP 5-aminoisophthalate, were hydrothermally synthesized and characterized by single-crystal X-ray diffraction,
IR spectra, thermogravimetric analyses, and variable-temperature magnetic susceptibility measurements. The two
complexes are constructed from the same Co (CO SBU, which is extended into a 1D chain in 1 and a 2D layer
2 n 2 2 n
] ‚3nH O (1) and [Co(AIP)(H O)]
(
)
2
2 2
)
in 2. As a result, 1 and 2 are 2D and 3D coordination polymers, respectively. The 3D supramolecular network of
complex 1 is held up by strong hydrogen bonds formed between carboxylate groups and shows very high stability
when the free H O molecules are removed, indicating an extraordinarily stable H-bonding system. Upon water
2
ligands being liberated, complex 2 becomes a stable microporous solid with coordination-unsaturated Co centers.
The behavior of the susceptibility curve of 1 suggests the occurrence of an interesting intrachain antiferromagnetic
coupling between the Co(II) ions and the presence of a significant orbital contribution, whereas the features of 2
indicate an antiferromagnetic coupling with T
induced magnetic transition.
N
)
3.5 K and a long-range antiferromagnetic order with a field-
Introduction
frameworks is hydro(solvo)thermal assembly by incorporat-
ing appropriate metal ions (connectors) with multifunctional
bridging ligands (linkers). However, the hydro(solvo)thermal
The current interest focused on the crystal engineering of
coordination polymeric frameworks stems not only from their
potential application as new functional solid materials but
also from their intriguing architectures and topologies. One
of the most effective approaches to obtain polymeric
5
reaction is highly influenced by many factors, such as the
oxidation state and coordination geometry of the metal center,
temperature, pH value, metal-to-ligand ratio, ligands, sol-
vents, and counterions. In many cases, a subtle alteration in
any of these factors can lead to totally different products. A
great deal of work on hydro(solvo)thermal synthesis with
N-donor rigid heteroaromatic ligands, such as pyridinecar-
1
,2
3,4
*
To whom correspondence should be addressed. E-mail: yyg@fjirsm.ac.cn
(
Y.-G.Y.). Fax: (86)-591-83714946.
†
Fujian Institute of Research on the Structure of Matter, The Chinese
Academy of Sciences.
‡
6,7
Fujian Normal University.
Massachusetts General Hospital and Harvard Medical School.
boxylate or 4,4′-bipyridine, has already been reported.
§
However, there has been relatively little effort on the
transition metal amino benzoate polymers, mainly because
(
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6276 Inorganic Chemistry, Vol. 45, No. 16, 2006
10.1021/ic0602244 CCC: $33.50
© 2006 American Chemical Society
Published on Web 07/11/2006

Stable Supramolecular Microporous Co(II) Complexes
of the more flexible coordination manner of the amino group
under hydro(solvo)thermal conditions.
Table 1. Collected Crystallographic Data and Parameters for 1 and 2
1
2
Meanwhile, one of the challenges in microporous coor-
dination polymeric frameworks is their fragility. Unlike their
inorganic analogues, which are held together with rugged
covalent bonds, coordination polymeric molecules are always
glued with relatively weak coordination or supramolecular
interactions. Although numerous coordination networks with
interesting structural aspects have been reported,8,9 the porous
metal-organic coordination networks extended via hydrogen
bonds often show poor thermal stability. Stable networks
sustained by hydrogen-bond interactions are still rare or
formula
Mr
cryst syst
space group
a (Å)
C16H18CoN2O11
473.25
monoclinic
C2/c
28.4110(9)
4.4718(2)
15.3333(6)
116.852(2)
1738.02(12)
4
1.809
1.059
2537
1538
0.0432, 0.1202
0.0475, 0.1266
C8H7CoNO5
256.08
monoclinic
P2(1)/c
8.835(4)
12.519(5)
7.908(3)
97.532(4)
867.1(6)
4
1.962
1.978
6571
1991
0.0343, 0.0844
0.0373, 0.0865
b (Å)
c (Å)
â (deg)
3
V (Å )
Z
Dcalcd (mg cm-3)
-
1
µ (mm
)
range for data collection
no. of independent reflns
final R1, wR2 [I > 2σ(I)]
R1, wR2 indices (all data)
lacking.1 To explore new microporous and magnetic
0
materials,11-15
our current research has focused on the
synthesis of highly stable microporous open frameworks,
especially those held up by hydrogen-bond interactions.
Herein, we report the crystal structures and magnetic
properties of two highly stable 3D cobalt(II) supramolecular
(
15 mL) was sealed in a Teflon-lined stainless steel vessel and
heated at 433 K for 3 days under autogenous pressure. Deep red
crystals were produced when the mixture was slowly cooled to room
temperature (yield: 60%, on the basis of Co). Anal. Calcd for
C H18CoN O11: C, 40.61; H, 3.83; N, 5.92. Found: C, 40.58; H,
16 2
3
polymers, [Co(HAIP)
AIP ) 5-aminoisophthalate, which were prepared by the
hydrothermal reaction of CoSO ‚7H O with H AIP under
2 n 2 2 n
] ‚3nH O (1) and [Co(AIP)H O] (2),
-
1
.77; N, 5.90. IR (KBr pellet, cm ): 3312 (vs), 3272 (vs), 1683
4
2
2
(
7
s), 1605 (s), 1475 (vs), 1396 (s), 1331 (s), 1256 (vs), 963 (vs),
69 (vs), 513 (w).
different pH conditions. The strong hydrogen-bond interac-
tions extend complex 1 into a 3D open supramolecular
architecture, and it exhibits extraordinarily high stability. In
Synthesis of [Co(C
8
NH
O (0.50 mmol), AIP (1.00 mmol), C
2
O (5 mL) was adjusted to 7.5 by 10% KOH under
5
O
4
)(H
2
O)]
n
(2). The pH value of a
mixture of CoSO
5 mL), and H
4
‚7H
2
2 5
H OH
2, Co(II) cations link AIP ligands to yield a 3D network
(
containing microporous channels viewed along the c axis,
which are filled by coordinated water molecules. Thermo-
gravimetric studies show the microporous channels could
contain open metal sites when coordination water molecules
are eliminated.
vigorous stirring. The mixture was sealed in a Teflon-lined stainless
steel vessel and heated at 433 K for 3 days under autogenous
pressure. Deep red crystals were produced when the mixture was
slowly cooled to room temperature (yield: 48%, on the basis of
Co). Anal. Calcd for C
8 7 5
H CoNO : C, 37.52; H, 2.76; N, 5.47.
-
1
Found: C, 37.48; H, 2.70; N, 5.42. IR (KBr pellet, cm ): 3354
(
s), 3173 (s), 1682 (vs), 1539 (vs), 1466 (vs), 1162 (w), 720 (w).
Crystallographic Measurements. All of the diffraction data
Experimental Section
General. All chemicals and reagents are commercially available
were collected on a Siemens SMART CCD diffractometer with
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) at a
temperature of 293(2) K, using the ω-2θ scan technique (1.61° <
θ < 25.02°). The intensity data were corrected by Lp factors and
empirical absorption. The structure was solved by direct methods
and were used as received without further purification. Infrared
-1
spectra (KBr pellets) were recorded in the range of 400-4000 cm
on a Nicolet Magna 750 FT-IR spectrometer. The C, H, and N
microanalyses were recorded on an Elemental Vario EL III
elemental analyzer. Thermogravimetric analyses (TGA) were
performed on a Mettler Toledo TGA 851e analyzer under nitrogen
2
and refined by full-matrix least-squares techniques on F using
SHELXTL-97.16 The non-hydrogen atoms were refined anisotro-
pically, and the hydrogen atoms on carbon atoms and those of amido
as well as carboxyl were added according to theoretical models;
the hydrogen atoms of O1W and O2W were positioned geo-
metrically. Crystal data and details of the structure determination
are summarized in Table 1, and the selected bond lengths and angles
for the two complexes are given in Table 2.
-1
with a heating rate of 10 °C min . Powder X-ray diffraction (XRD)
data were obtained using a Philips X’Pert-MPD diffractometer with
Cu KR radiation (λ ) 1.54056 Å). Variable-temperature magnetic
susceptibility and magnetization measurements were performed on
a Maglab System 2000 magnetometer. The experimental suscep-
tibilities were corrected for the diamagnetism of constituent atoms.
Synthesis of [Co(C
8
NH
6
O
4
)
2
]
n
‚3nH
2
O (1). A mixture of CoSO
OH (2 mL), and H
4
‚
O
7
H
2
O (1.0 mmol), H AIP (1.00 mmol), C
2
2
H
5
2
Results and Discussion
Crystal Structures of [Co(C
8
NH
6
O
4
)
2
]
n
2
‚3nH O (1).
(
8) Li, H.; Eddaoudi, M.; O’Keeffe, M.; Yaghi, O. M. Nature 1999, 402,
76.
Single-crystal X-ray diffraction study reveals that 1 has a
porous 3D supramolecular network linked by both coordinat-
ing and hydrogen bonds. As illustrated in Figure 1, the Co-
(II) atom is located in the elongated octahedral environ-
ment: four oxygen atoms from four different AIP ligands
in the equatorial plane and two N atoms from two different
AIP ligands in the apical positions. The AIP ligand in 1 uses
one of its two carboxylate groups to bidentate two cobalt-
2
(
9) (a) Gutschke, S. O. H.; Molinier, M.; Powell, A. K.; Wood, P. T.
Angew. Chem., Int., Ed. 1997, 38, 991. (b) Brunet, P.; Simard, M.;
Wuest, J. D. J. Am. Chem. Soc. 1997, 119, 2737.
(
10) (a) Cheng, D.; Khan, M. A.; Houser, R. P. Inorg. Chem. 2001, 40,
6858. (b) Choi, H. J.; Suh, M. P. Inorg. Chem. 1999, 38, 6309.
(
(
(
11) Beauvais, L. G.; Long, J. R. J. Am. Chem. Soc. 2002, 124, 12096.
12) Pan, L.; Ching, N.; Huang, X.-Y.; Li, J. Inorg. Chem. 2000, 39, 5333.
13) Huang, Z.-L.; Drillon, M.; Masciocchi, N.; Sironi, A.; Zhao, J.-T.;
Rabu, P.; Panissod, P. Chem. Mater. 2000, 12, 2805.
(
14) Fujita, M.; Kwon, Y. J.; Washizu, S.; Ogura, K. J. Am. Chem. Soc.
1994, 116, 1151.
(
15) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe;
(16) Sheldrick, G. M. SHELXTL-97, Program for Crystal Structure
Refinement; University of G o¨ ttingen: G o¨ ttingen, Germanny, 1997.
M.; Yaghi, O. M. Science 2002, 295, 469.
Inorganic Chemistry, Vol. 45, No. 16, 2006 6277

Tang et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1 and 2a
Complex 1
Co(1)-O(3)#1
Co(1)-O(3)#2
Co(1)-O(4)#3
Co(1)-O(4)#4
Co-N(1)
2.088(2)
2.088(2)
2.097(2)
2.097(2)
2.215(3)
2.215(3)
O(3)#1-Co(1)-O(3)#2
O(3)#1-Co(1)-O(4)#3
O(3)#1-Co(1)-O(4)#4
O(3)#1-Co(1)-N(1)
O(4)#3-Co(1)-N(1)
180.00(1)
92.44(9)
87.56(9)
87.31(10)
90.57(9)
Co(1)-N(1)#5
Complex 2
Co(1)-O(1)#1
Co(1)-O(2)
Co(1)-O(1W)
Co(1)-O(4)#2
Co(1)-N(1)#3
Co(1)-O(3)#2
1.9928(2)
2.0180(2)
2.0980(2)
2.1228(2)
2.220(2)
O(1)#1-Co(1)-O(2)
O(1)#1-Co(1)-O(1W)
O(2)-Co(1)-O(1W)
O(1)#1-Co(1)-O(4)#2
O(2)-Co(1)-O(4)#2
O(1W)-Co(1)-O(4)#2
108.67(8)
88.43(7)
90.58(7)
155.86(7)
95.45(7)
90.20(7)
Figure 2. (a) One-dimensional Co2(CO2)2 chain in 1, Co‚‚‚Co separated
by 4.472 Å. (b) Three-dimensional open supramolecular architecture pillared
by strong hydrogen bonds. The pores are occupied by free water molecules
represented by magnified red balls for clarity.
2.2485(2)
a
Symmetry transformations used to generate equivalent atoms: For 1:
1
1
1
1
1
1
#
1 x, -y + 1, z + /2 #2 -x + /2, y - /2, -z + /2 #3 -x + /2, y + /2,
1 1 1 1
-
+
-
z + /2 #4 x, -y, z + /2 #5 -x + /2, -y + /2, -z + 1. For 2: #1 -x
1 1 3 1
1, -y + 1, -z #2 -x + 2, y - /2, -z + /2 #3 x, -y + /2, z + /2 #4
1
1
x + 2, y + /2, -z + /2.
Figure 3. View of the coordination environment of Co in 2 (a: 2 - x,
Figure 1. View of the coordination environment of Co in 1 (a: 1/2 - x,
1
1
3
1
-
/2 + y, /2 - z; b: x, /2 - y, /2 + z; C: 1 - x, 1 - y, -z).
1
1
1
1
1
1
/
2 + y, /2 - z; b: /2 - x, - /2 + y, /2 - z; c: x, -y, /2 + z, d: x, 1 -
1 1 1
y, /2 + z, e: /2 - x, /2 - y, 1 - z).
the coordination model in 1, the coordination modes of AIP
ligands in 2 can be described as follows: one of its two
carboxylate groups, acting as a bidentate ligand, bridges two
Co(II) centers and the other one coordinates to a third Co-
(II) center as bidentate, whereas the amino group bonds to
the fourth Co(II) center. The secondary building unit (SBU)
(
II) atoms, whereas the other carboxylate group does not
participate in coordination to the Co(II) center. The amino
group of AIP coordinates to the third cobalt(II) atom.
The secondary building unit (SBU) of 1 is a dicobalt
dicarboxylate Co
separated by 4.472 Å, are bridged by two µ
carboxylate groups. The Co (CO SUBs are lined up into
a 1D chain along the b axis by sharing the Co(II) atom. This
D chain is further linked by two N atoms from two adjacent
2
2 2
(CO ) , in which the two Co atoms,
2
-bridging
2 2 2
of 2 is also a dicobalt dicarboxylate SBU Co (CO ) , with a
2
2
)
2
Co‚‚‚Co distance 4.3 Å. If we omit Co-N bonds, the
binuclear subunits are interconnected through Co-O bonds
into a 2D layer (Figure 4a). The 2D layers are assembled
into an unprecedented 3D framework via Co-N bonds. As
1
chains into a 2D layer propagating along the bc plane. It is
noteworthy that one of the two carboxylate groups of each
AIP ligand does not participate in the coordination, but acts
as a hydrogen-bond acceptor and donor. As shown in Figure
a contrast to complex 1, the H
but coordinated to a Co(II) center. If we omit H
2
O molecule in 2 is not free
O molecules
2
2
in 2, a pore with the dimensions of ca. 7 × 6 Å is observed
along the c axis. Two water molecules, acting as the disguise
guests, are filled inside the void of the pore. Because the
metal-AIP coordination bonds are much stronger than the
metal-water bonds, it is expected that water liberation by
heating will facilitate complex 2 into a coordination-
unsaturated microporous complex. The coordination-unsatur-
ated metal site can consequently serve as the binding site to
2
b, there exist strong hydrogen bonds between two carboxy-
late groups from two different AIP ligands (O‚‚‚O ) 2.598-
(
4) Å, O-H‚‚‚O ) 162(10)°). The hydrogen bonds pillar
the layers into a 3D supramolecular open framework with a
2
pore along the a axis (approximate dimensions 7.9 × 13 Å ),
which is occupied by free and removable water molecules.
Crystal Structures of [Co(C
X-ray diffraction analysis reveals that complex 2 exhibits a
D metal-organic framework. As shown in Figure 3, the
8 5 4 2 n
NH O )(H O)] (2). The
1
7,18
other inclusions.
3
If we take the binuclear SBU to be a single node, such a
SBU becomes a 6-connected node, and each AIP2 ligand
can be regarded as a three-connected vertex that links three
-
asymmetric unit contains one Co atom, one AIP ligand, and
one coordinated water molecule. All the equivalent Co(II)
atoms are coordinated by four oxygen atoms and one N atom
from four different AIP ligands, as well as one H O. Each
2
AIP ligand employs its carboxylate groups and amino group
in turn to coordinate to four Co(II) centers. Different from
(
17) (a) Yaghi, O. M.; Li, H. L.; Groy, T. L. J. Am. Chem. Soc. 1996, 118,
9096-9101.
(18) Copp, S. B.; Subramanian, S.; Zaworotko, M. J. Angew. Chem., Int.
Ed. 1993, 32, 706-709.
6278 Inorganic Chemistry, Vol. 45, No. 16, 2006

Stable Supramolecular Microporous Co(II) Complexes
Figure 4. (a) Two-dimensional layer generated from the binuclear SBU via Co-O bonds. (b) Three-dimensional stacking structure of 2 where the H2O
ligands are represented by magnified red balls for clarity. (c) Topological representation of 2.
SBUs. The linkage of three- and six-connected vertexes is
illustrated in Figure 4c. This framework is a distorted (3,
2
6
(
(
)-connected net with the Schl a¨ fli symbol being (4.6 )
2
-
2
10
3
4 .6 .8 ), but it is obviously different from the other reported
3, 6)-connected net of the same Schl a¨ fli symbol (such as
rutile (rtl) or sit net). An interesting feature of this net is
the presence of parallel single helices running through the
structure, as highlighted in Figure 4c. The six-connected
19
nodes act as hinges of four 2
whereas the three-connected nodes act as hinges of two edge-
sharing 2 helices with different handedness. As an overall
1
helices with equal handedness,
1
effect, these connections make the net racemic.
IR Spectra. The IR spectra of 1 and 2 show the
characteristic bands of the AIP ligand between 1630 and
Figure 5. TGA plots of complexes 1 and 2.
-
1
1
460 cm for the asymmetric vibration and between 1441
-
1
and 1367 cm for the symmetric vibration, and the broad
bands of water between 3215 and 3442 cm . The charac-
teristic bands at 1684 cm in 1 are attributed to the
protonated carboxylate groups of AIP. In 2, the absence of
-
1
-
1
-1
the expected characteristic bands at 1730-1680 cm , which
are attributed to the protonated carboxylate group, indicate
the complete deprotonation of AIP in 2.20 The respective
values of [νasym(CO
ence of a bridging mode (162 cm ) in complex 1 and both
2
2
)-νsym(CO )] clearly indicate the pres-
-
1
-1
-1
the chelating mode (79 cm ) and bridging mode (130 cm )
2
1
in complex 2. These results are consistent with that of the
X-ray analysis.
Figure 6. XPRD patterns for 1: (A) the simulated pattern, (B) taken at
room temperature, (C) after heating at 130 °C for 2 h, and (D) after heating
at 350 °C for 2 h.
Thermogravimetric Studies and X-ray Powder Dif-
fraction. The thermogravimetric analysis (TGA) of complex
To examine the porous properties of the materials, we
heated the synthesized crystal samples of 1 at 130 and 350
1
reveals that there are three stages of weight loss in the
temperature range of 30-600 °C (Figure 5). The first stage,
occurring between 30 and 90 °C, is attributed to the loss of
three uncoordinated water molecules per formula (observed
weight loss, 10.6%; calcd, 11.4%). The weight is almost
unchanged in the second stage in a very long temperature
range (90-375 °C). Above 375 °C, the product begins to
decompose. The TGA curve of the free AIP ligand shows
that it decomposes at 303 °C. This means that complex 1 is
more stable than the free AIP ligand, and the H bonds
between these two carboxylic groups are strong enough to
withstand the high temperature of 375 °C.
°
C for 2 h; the position of the most intensive line remain
unchanged relative to that of the single crystal (Figure 6),
which shows us the extraordinary thermal stability relies on
the hydrogen-bonding interactions. 1 also exhibits the ability
to absorb water expediently in this process when exposed
in atmosphere, indicating a reversible process; thus, 1 can
be envisaged as a good candidate for a new molecular sieve.22
The TGA analysis for 2 showed the following two
strikingly clean and well-separated weight-loss steps. In the
first region (30-260 °C), it lost coordinated water molecules
(8% observed, 7% calcd). On further heating, 2 lost weight
(
(
(
19) Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. CrystEng-
continuously, corresponding to preliminary decomposition
at 370 °C and fast decomposition around 480 °C. The
synthesized crystal samples of 2 were heated at 350 °C for
Comm 2004, 6(65), 377-395.
20) Bellamy, L. J. The Infrared Spectra of Complex Molecules; Wiley:
New York, 1958.
21) (a) Deacon, G. B.; Phillips, R. J.Coord. Chem. ReV. 1980, 33, 227.
(b) Nakamoto, K. Infrared Spectra and Raman Spectra of Inorganic
(22) Breck, D. W. Zeolite Molecular SieVes, Structure, Chemistry, and Use;
and Coordination Compounds; John Wiley & Sons: New York, 1986.
John Wiley & Sons: New York, 1974.
Inorganic Chemistry, Vol. 45, No. 16, 2006 6279

Tang et al.
Weiss constant is consistent with the antiferromagnetic
interactions between Co(II) centers.
According to the structure of 1, it could be presumed that
the main magnetic interactions between the metal centers
might happen between two carboxylate-bridged 1D chains,
whereas the superexchange interactions between Co(II) ions
through the AIP bridge can be ignored because of the length
of the AIP ligands. Because of the spin-orbit coupling
contribution of Co(II) ions, it is difficult to find an accurate
analytical expression to describe the temperature dependence
of the magnetic susceptibility for chains of Co(II) ions. To
obtain an estimate of the strength of the antiferromagnetic
coupling, we used a simple phenomenological equation
Figure 7. XPRD patterns for 2: (A) the simulated pattern, (B) taken at
room temperature, and (C) after heating at 350 °C for 2 h.
2
3
proposed by Masciocchi and Rabu, øT ) A exp(-E
B exp(-E /kT), to fit the magnetic data of 1. Here, A +
B equals the Curie constant, E and E represent the
1
/kT)
+
2
1
2
“
activation energy” corresponding to the spin-orbital cou-
pling and the antiferromagnetic exchange interaction, re-
spectively. The least-squares fit (the agreement factor R )
2
2
-4
∑
[(ø
M
T)obs - (ø
M
T)calcd] /∑(ø
M
T)obs ) 8.2 × 10 ) of the
experimental data to the above expression led to A + B )
.87 emu K mol and E
those given in the literature for the Curie constant and the
effect of spin-orbit coupling. The value of -E /k ) -9.1
-
1
2
1
/k ) 45.7 K, in agreement with
2
4
2
Figure 8. Plots of the temperature dependence (from 300 to 2 K) of øMT
and øM (solid) in 1 at a field of 1000 G. The magnetic susceptibility was
measured using two consecutive cycles, each from 2 to 300 K and back.
As no variation was observed, a representative cycle (2-300 K) is shown.
K, obtained for the antiferromagnetic coupling, is more
negative than the values found in coordination polymer
chains of the Co(II) ions bridged by the carboxylate in the
anti-anti conformations, indicating that a stronger antifer-
romagnetic exchange interaction is mediated by the double
carboxylate bridge in syn-syn conformations.
The molar magnetization data for 1 in the form of M versus
H in the field range 0-5 T at 2 K is shown in the inset of
Figure 9. The magnetization under 5 T at 2 K is only 0.32
Nâ per Co(II) ion, far from the saturation value of 2.1-2.5
Nâ expected for a Co(II) ions with S )1/2, and g ) 4.1-5
2
5
at low temperature, strongly suggesting antiferromagnetic
coupling between Co(II) ions in 1.
The magnetic properties of 2 in the form of plots of both
Figure 9. Plot of temperature dependence (from 300 to 2 K) of øM-1 at
a field of 1000 G. The insert is the magnetization curve of 1 at 2 K.
-
1
ø
M
T and ø
M
M
versus T are shown in Figure 10. The ø T
-
1
value per Co(II) at 300 K is 3.1 emu K mol , higher than
2
h; the position of the most intensive line remain unchanged
the expected spin-only value for a magnetically isolated Co-
II) ion because of the orbit contribution. The ø T value
M
relative to the simulated diffraction patterns (Figure 7). This
experiment also indicates the high thermal stability of 2.
Magnetic Properties. The magnetic properties of 1 in the
(
decreases slightly from room temperature to 120 K and then
-1
rapidly decreases to 0.45 emu K mol at 2 K. The magnetic
form of ø
M
T and ø
M
M
versus T (ø being the molar magnetic
susceptibility versus T plot exhibits a maximum at 3.5 K
under an applied magnetic field of 2000 Oe. All these
susceptibility) plots are shown in Figure 8. Data were
collected between 2 and 300 K in an applied field of 1000
features indicate an antiferromagnetic coupling in 2 with T
3.5 K and a long-range antiferromagnetic order. The 10-
N
-1
Oe. The ø
higher than the spin-only value of 1.875 emu K mol
expected for a magnetically isolated Co(II) system with S
3/2. Upon cooling, the ø T values continuously decrease,
M
T value at room temperature is 2.60 emu K mol ,
)
3
-
1
-1
00 K temperature dependence of ø
M
was fit by the Curie-
-1
-1
Weiss expression with C values of 3.18 emu K mol and
θ values of -10.8 K. The negative θ values also indicate
)
M
with a value very close to zero at 2 K. The susceptibility
curve shows a broad maximum at 15 K. This behavior
suggests the occurrence of a relatively important intrachain
antiferromagnetic coupling between the Co(II) ions and the
presence of a significant orbital contribution. The temperature
(
23) Rueff, J.-M.; Masciocchi, N.; Rabu, P.; Sironi, A.; Skoulios, A. Eur.
J. Inorg. Chem. 2001, 2843-2848.
24) (a) Rueff, J. M.; Masciocchi, N.; Rabu, P.; Sironi, A.; Skoulios, A.
Chem.sEur. J. 2002, 8, 1813. (b) Carlin, R. L. Magnetochemistry;
Springer-Verlag: Berlin, 1986.
(25) (a) Drillon, M.; Coronado, E.; Belaiche, M.; Carlin, R. L. J. Appl.
Phys. 1988, 63, 3551. (b) Konar, S.; Mukherjee, P. S.; Zangrando,
E.; Floret, F.; Chaudhuri, N. R. Angew. Chem., Int. Ed. 2002, 41, 1561.
(c) Robinson, W. K.; Friedberg, S. A. Phys. ReV. 1960, 117, 402.
(
-
1
dependence of ø
M
between 300 and 25 K (Figure 9)
approximates Curie-Weiss behavior with C ) 2.96 emu K
-
1
mol and θ ) -41.2 K. The negative sign of the Curie-
6280 Inorganic Chemistry, Vol. 45, No. 16, 2006

Stable Supramolecular Microporous Co(II) Complexes
Figure 10. Plots of the temperature dependence (from 300 to 2 K) of
øMT and øM of 2 in a field of 2000 G; the solid line represents the best
theoretical fit. The insert is the magnetization curve of 2 at 2 K.
Figure 12. Plots of the field-dependent magnetization of 2 at 2 K with
the critical field being ca. 2 T.
-
1
an extended 3D framework. As the Co‚‚‚Co distance over
the carboxylate bridge (4.3 Å) is much shorter than those
over the AIP spacers (6.05-8.86 Å), the exchange coupling
through the carboxylate bridge should be dominant. The
field-induced magnetic transition in 2 is similar to some
observations in metal phosphonates containing dimer units
in ladderlike chain structures; the critical field is slightly less
than those found in Co(II) phosphonates despite a larger M‚
‚M distance (4.3 Å) relative to the M-O-M bond angle.2
7,29
‚
As a comparison, the magnetic behavior of the dehydrated
product of 2 has been performed and the value of T
N
remained, together with the same S-shaped curve, in field-
dependent magnetization of 2 at 2 K. (See Figures S1 and
S2 in the Supporting Information.)
Figure 11. Evolution of the magnetic susceptibility of 2 as a function of
the temperature, measured on cooling under an external magnetic field (2,
1
.5, 1T, 0.2, and 0.1 T, from top to bottom in the plot) as noted on the
graph.
Conclusion
antiferromagnetic coupling between the metal sites. Consid-
Two novel, highly stable supramolecular complexes have
been synthesized. The structural and thermal characterization
of both display stable microporous 3D open frameworks. The
water molecules, acting as the guest molecules in 1 and as
the disguise guest molecules (which occupied the pore in
the architecture by coordinating to the metal and could be
removed easily like the guest molecules) in 2, are distinct
in these two complexes. The behavior of both polymers 1
and 2 corresponds to an antiferromagnetically coupled
system, and field-induced magnetic transition is observed
2 2 2
ering that the Co‚‚‚Co distance (4.3 Å) within the Co (CO )
SUB is much shorter than those for interdimer distances (6.05
and 8.86 Å), the observed antiferromagnetic interaction
should mainly arise from the exchange between the magnetic
centers within Co2 dimers. The susceptibility data were thus
approximately analyzed by an isotropic dimer mode of spin
2
6
S ) 3/2; fitting the experimental data above 30 K gave J
-
1
-5
)
-1.33 cm , g ) 2.77, and R ) 8.04 × 10 . It is
interesting to note that the susceptibility maximum of 2
depends on the magnitude of the applied magnetic field (H).
A broadening of this maximum is observed as long as the
field is increased, and it disappears when the applied field
is greater than 2 T (Figure 11), suggesting the occurrence
of a field-induced magnetic transition.
2
in 2. Upon liberating coordinated H O molecules, complex
2 has interesting coordination-unsaturated Co sites. These
works reveal that the solvents and the pH value play very
important roles in the formation of different coordination
frameworks, and this offers the possibility of controlling the
formation of such network structures by varying those
factors.
The field-dependent magnetization of 2 at 2 K has an
S-shaped curve, indicating the occurrence of a magnetic
transition from the antiferromagnetic ground state to a spin-
polarized state.27 The critical field, determined by the dM/
dH curve, is ca. 2 T at 2 K, consistent with the observations
of temperature-dependent magnetic susceptibilities under
different applied fields (Figure 12). The magnetization at 5
T is 2.27 Nâ, close to the saturation value of ca. 2.3 Nâ
Acknowledgment. This work was supported by the
National Natural Science Foundation of China under Project
2
0173063, the State Key Basic Research and Development
Plan of China (001CB108906), and the NSF of Fujian
Province (E0020001).
2
8
expected for a Co(II) ion with S ) 1/2 and g ) 4.6.
Supporting Information Available: Plots of the magnetic
behavior of dehydrated 2 (pdf) and crystallographic information
data for 1 and 2 (cif). This material is available free of charge via
the Internet at http://pubs.acs.org.
In the structure of 2, the double-carboxylate-bridged
dinuclear Co(II) units are connected by AIP spacers to form
(
(
(
26) Liu, Y. H.; Tsai, H. L.; Lu, Y. L.; Wen, Y. S.; Wang, J. C.; Lu, K. L.
Inorg. Chem. 2001, 40, 6426.
27) Zheng, L.-M.; Gao, S.; Yin, P.; Xin, X.-Q. Inorg. Chem. 2004, 43,
IC0602244
2
151.
28) Caneschi, A.; Dei, A.; Gatteschi, D.; Tangoulis, V. Inorg. Chem. 2002,
1, 3508.
(29) Yin, P.; Gao, S.; Wang, Zh.-M.; Yan, Ch.-H.; Zheng, L.-M.; Xin,
4
X.-Q. Inorg. Chem. 2005, 44, 2761.
Inorganic Chemistry, Vol. 45, No. 16, 2006 6281