Tetracarboxylate-based Co(II), Ni(II) and Cu(II) three-dimensional coordination polymers: Syntheses, structures and magnetic properties

Article abstract of DOI:10.1039/c001655a

Methylenediisophthalic acid (H₄MDIP), as semi-rigid 'V'-shaped carboxylate ligands, react with CoO, NiO and Cu(NO₃) ₂·3H₂O to give three novel coordination polymers [H₃O]₂[Co₃(MDIP)₂]·2DMF (1), [Ni₂(HMDIP)(μ₂-OH)(H₂O)₃(DMF)] ·4H₂O·DMF (2) and [Cu₃(MDIP) (μ₂-OH)₂(H₂O)₄]·6.5H ₂O (3) (DMF = N,N′-dimethylformamide). All compounds have been characterized by thermogravimetric analysis, IR spectroscopy, elemental and single-crystal X-ray diffraction analyses. Complex 1 is an unusual open anionic framework that is defined as the metal-organic replica of fluorite. Both 2 and 3 features a 3D open framework with one-dimensional elliptical channels and R- and L-helical chains, and their resulting frameworks can be rationalized as crb and pts topology respectively. An interesting feature of complex 3 is the presence of the linear Cu₃ units that is formed by carboxylate and μ₂-hydroxyl groups linking three Cu(II) metal centers. Magnetic investigations indicate that ferromagnetic couplings are dominant in the three compounds. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c001655a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Tetracarboxylate-based Co(II), Ni(II) and Cu(II) three-dimensional
coordination polymers: syntheses, structures and magnetic properties†
Shengqun Su,a,b Zhiyong Guo,a,b Guanghua Li,c Ruiping Deng,a Shuyan Song,a,b Chao Qin,a Chengling Pan,a
Huadong Guo,a Feng Cao,a,b Song Wanga,b and Hongjie Zhang*a
Received 25th January 2010, Accepted 6th July 2010
DOI: 10.1039/c001655a
Methylenediisophthalic acid (H4MDIP), as semi-rigid ‘V’-shaped carboxylate ligands, react with CoO,
NiO and Cu(NO3)2·3H2O to give three novel coordination polymers [H3O]2[Co3(MDIP)2]·2DMF (1),
[Ni2(HMDIP)(m2-OH)(H2O)3(DMF)]·4H2O·DMF (2) and [Cu3(MDIP)(m2-OH)2(H2O)4]·6.5H2O (3)
(DMF = N,N¢-dimethylformamide). All compounds have been characterized by thermogravimetric
analysis, IR spectroscopy, elemental and single-crystal X-ray diffraction analyses. Complex 1 is an
unusual open anionic framework that is defined as the metal–organic replica of fluorite. Both 2 and 3
features a 3D open framework with one-dimensional elliptical channels and R- and L-helical chains,
and their resulting frameworks can be rationalized as crb and pts topology respectively. An interesting
feature of complex 3 is the presence of the linear Cu3 units that is formed by carboxylate and
m2-hydroxyl groups linking three Cu(II) metal centers. Magnetic investigations indicate that
ferromagnetic couplings are dominant in the three compounds.
formed. As far as we know, coordination polymers constructed
Introduction
from the H4MDIP ligand have rarely been reported.1
In recent years, research on coordination polymers (CPs) has been
On the other hand, the first row transition metals (Co, Ni and
rapidly expanding, not only for their potential applications in gas
Cu) complexes have attracted extensive interest in recent years
storage, ion exchange, catalysis, magnetism and luminescence1–5
but also for their unique characteristics, such as structural regu-
because their different oxidation states allow two important
parameters to be varied, i.e. spin quantum number and magnetic
larity, flexibility, and functionalized high surface area.6 Among the
reported studies about the construction of complexes, carboxylate
ligands have been extensively used due to their versatile coordina-
tion conformations and strong coordination ability.7 Until now,
much research has been devoted to the use of rigid carboxylate
ligands, such as 1,4-benzenedicarboxylic acid (p-H2BDC), 1,3-
benzenedicarboxylic acid (m-H2BDC), 1,3,5-benzenetricarboxylic
acids (H3BTC) and so on.8–10 Meanwhile, many interesting metal–
organic frameworks based on flexible carboxylate ligands have also
been reported widely.11 But, in contrast, the investigation into the
semi-rigid ‘V’-shaped carboxylate ligands is still in its infancy.12
anisotropy.14 These potential variable parameters would bring
about a great challenge in the field of magnetic coordination
polymers. So far the majority of magnetic frameworks are those
containing the above paramagnetic metal centers.
With the above idea in mind, herein we report three
unprecedented compounds, namely [H3O]2[Co3(MDIP)2]·2DMF
(1),
[Ni2(HMDIP)(m2-OH)(H2O)3(DMF)]·8H2O
(2)
and
[Cu3(MDIP)(m2-OH)2(H2O)4]·6.5H2O (3) based on the assembly
of H4MDIP with cobalt(II), nickel(II) or copper(II) metal ions.
The thermal and magnetic properties of these compounds are
discussed.
Methylenediisophthalic acid (H4MDIP) is
a ‘V’-shaped
tetracarboxylate ligand which can afford metal centers a variety of
connection modes, thereby generating abundant structural motifs.
At the same time, this ligand is relatively flexible, since the phenyl
rings can freely rotate around the methylene (–CH2–) groups
according to the small change in the coordination environment
with the result that various coordination conformations are
Experimental
Materials and measurements
Methylenediisophthalic acid (H4MDIP) was synthesized as re-
ported in the literature,15 and the other reagents were purchased
from commercial sources and used as received. IR spectra
were obtained from KBr pellets on a Perkin–Elmer 580B IR
spectrometer in the 400–4000 cm-1 region (SI). Elemental analyses
(C, H, N) were performed with a VarioEL analyzer. Thermo-
gravimetric analysis (TGA) was performed on a Perkin–Elmer
TG-7 analyzer heated from 40 to 700 ◦C under nitrogen. Powder
X-Ray diffraction data were collected on a Bruker D8-ADVANCE
diffractometer equipped with Cu-Ka at a scan speed of 2◦ min-1.
Temperature-dependent magnetic measurements were carried out
on a Quantum Design SQUID MPMS-7 magnetometer with
an applied field of 1000 Oe. The diamagnetic corrections for
aState Key Laboratory of Rare Earth Resource Utilizations, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun,
130022, P. R. China. E-mail: hongjie@ciac.jl.cn; Fax: +86 431 85698041;
Tel: +86 431 85262127
bGraduate School of the Chinese Academy of Sciences, Beijing, 100039,
P. R. China
cState Key Laboratory of Inorganic Synthesis and Preparative Chemistry,
College of Chemistry, Jilin University, Changchun, 130012, P. R. China
† Electronic supplementary information (ESI) available: Experimental
details. CCDC reference numbers 763322–763324. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c001655a
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the compounds were estimated using Pascal’s constants,16 and
magnetic data were corrected for diamagnetic contributions of
the sample holder.
Table 1 Crystal data and structure refinements for complexes 1–3
1
2
3
Formula
Formula weight 1041.50
C40H36Co3N2O20
C20H39Ni2NO21 C17H31Cu3O20.50
Synthesis
746.94
Monoclinic
P21/c
200(2)
10.247(2)
15.250(3)
20.946(4)
99.91(3)
3224.4(11)
4
754.04
Orthorhombic
Pccn
Crystal system
Space group
T/K
Orthorhombic
Pbca
Synthesis of [H3O]2[Co3(MDIP)2]·2DMF (1). A mixture of
CoO (0.0150 g, 0.2 mmol), H4MDIP (0.0344 g, 0.1 mmol), DMF
(1.5 mL), and H2O (1.5 mL) was placed in a Teflon reactor
(20 mL) and heated at 105 C for 3 days. After the mixture was
gradually cooled to room temperature at a rate of 10 C h-1,
purple block crystals of 1 were obtained with 72% yield based
on H4MDIP. Anal. Calcd for C40H36Co3N2O20 (Mr = 1041.50): C,
46.12; H, 3.48; N, 2.69. Found: C, 46.23; H, 3.46; N, 2.78%. IR
(cm-1): 3419(m), 3012(m), 2806(m), 2508(w), 1407(m), 1623(s),
1588(s), 1540(s), 1464(s), 1429(s), 1377(s), 1252(m), 1141(w),
1103(m), 1018(w), 925(w), 881(w), 811(m), 775(m), 725(s), 710(m),
676(w), 610(w), 587(w), 522(w), 501(w), 450(m).
200(2)
16.223(3)
10.633(2)
25.188(5)
90.00
4345.0(15)
4
1.592
2124
22619
4263
0.0314
1.084
200(2)
˚
a/A
18.4609(10)
18.6553(10)
8.1387(4)
90.00
2802.9(3)
4
˚
b/A
◦
˚
c/A
◦
b (◦)
3
˚
V/A
Z
Dc/g cm-3
F(000)
1.539
1560
1.787
1536
Data collected
Unique data
R(int)
17162
6279
14433
2754
0.0337
1.110
0.0818
0.2023
0.0326
1.058
0.0446
0.1354
GOF on F2
a
R1 [I > 2s(I)]
0.0232
0.0600
wR2b(all data)
Synthesis of [Ni2(HMDIP)(l2-OH)(H2O)3(DMF)]·8H2O (2).
A mixture of NiO (0.0150 g, 0.2 mmol), H4MDIP (0.0344 g,
0.1 mmol), DMF (1.5 mL), and H2O (1.5 mL) was placed in a
Teflon reactor (20 mL) and heated at 105 ◦C for 3 days. After
the mixtur◦e was gradually cooled to room temperature at a
rate of 10 C h-1, green block crystals of 2 were obtained with
69% yield based on H4MDIP. Anal. Calcd for C20H39Ni2NO21
(Mr = 746.94): C, 32.16; H, 5.26; N, 1.88. Found: C, 31.87; H,
5.16; N, 1.93%. IR (cm-1): 3391(s), 2083(w),1631(s), 1592(m),
1547(m), 1446(s), 1376(s), 1242(w), 1108(w), 1064(w), 917(w),
873(w), 784(m), 776(m), 717(s), 668(m), 620(m), 549(m), 464(m).
1
a R1 = RꢀFo| - |Fcꢀ/R|Fo|. b wR2 = {R[w(Fo - Fc2)2]/R[w(Fo ) ]}
2
2 2
2
Descriptions of crystal structures
Structure of [H3O]2[Co3(MDIP)2]·2DMF (1). Single-crystal
X-ray diffraction reveals that compound 1 consists of carboxylate-
bridged tri-nuclear cobalt clusters. The Co1 atom, located on
the end of the Co3 unit, adopts a distorted octahedral geometry
coordinated by six oxygen atoms from four different MDIP4-
˚
ligands (Co–O 2.0276(11)–2.2432(12) A). The Co2 atom, situated
at an inversion center in the space group, also exhibits a distorted
octahedral geometry coordinated by six oxygen atoms from four
Synthesis of [Cu3(MDIP)(l2-OH)2(H2O)4]·6.5H2O (3). A mix-
ture of Cu(NO3)2·3H2O (0.0482 g, 0.2 mmol), H4MDIP (0.0344 g,
0.1 mmol), and H2O (15 ml) was placed in a beaker, and several
drops of aqueous ammonia was added under stirring until the
mixture became clear. The blue solution was filtered and allowed
to slowly evaporate at room temperature to isolate a blue rod-like
crystalline solid 3 with 52% yield based on H4MDIP. Anal. Calcd
for C17H31Cu3O20.50 (Mr = 754.04): C, 27.08; H, 4.41. Found: C,
27.13; H, 4.56%. IR (cm-1): 3401(m), 1610(m), 1568(s), 1449(m),
1411(m), 1359(m), 1239(m), 1119(w), 970(w), 907(w), 883(w),
800(m), 783(m), 733(m), 653(m), 564(m), 480(m).
different [MDIP]4- ligands (Co–O 2.0515(11)–2.1650(11) A). The
˚
Co2 atom is linked to two neighboring Co1 by four –O–C–O–
bridges and a pair of m2-Ocarboxyl atoms (O1 and O1A) to afford a
˚
Co3 core with a Co ◊ ◊ ◊ Co distance of 3.569 A. (Fig. 1a). Each tri-
nuclear unit is further connected to neighboring others through
eight [MDIP]4- ions to generate an anionic 3D open framework
(Fig. 1b). The bond-valence calculations suggest all Co atoms are
in the +2 oxidation state.19 This result is also supported by an XPS
measurement of the compound in the energy region of Co2p1/2 and
Co2p3/2. The XPS spectrum (shown in Fig. S1†) gives one peak at
780.9 eV, attributable to Co2+.20 A negatively charged framework,
X-ray crystallography
2-
Co3(C8H4O4)4 and hydroxonium ion H3O+ occupy the voids
The X-ray intensity data for the three compounds were collected
on a Bruker SMART APEX CCD diffractometer with graphite
monochromatized Mo-Ka radiation (l = 0.71073 A). The crystal
based on the consideration of the charge balance. The effective
free volume calculated with PLATON for the inclusion is 1724.2
A per unit cell (after free molecules have been hypothetically
removed) corresponding to 39.68% of the cell volume.
3
˚
˚
structure was solved by means of Direct Methods and refined
employing full-matrix least squares on F2 (SHELXTL-97).17 All
the hydrogen atoms except for those of guest water molecules
were generated geometrically and refined isotropically using
the riding model. All non-hydrogen atoms were refined with
anisotropic displacement parameters except for some disordered
guest molecules. It should be noted that the guest molecules in the
channels of 1 and 2 are highly disordered and could not be modeled
properly so the diffused electron densities resulting from them
were removed by the SQUEEZE routine in PLATON.18 Crystal
data and details of the structure determination for complexes 1–3
are listed in Table 1. Selected bond lengths and angles are given in
Table S1.†
A better insight into the nature of the intricate framework can
be achieved by the application of a topological approach, which
is necessary to simplify the building blocks from which the 3D
net of 1 is built. As illustrated in Fig. 2, each [MDIP]4- ligand
can be considered as a four-connecting node since it links four
Co3 linear units and each Co3 unit in turn links eight [MDIP]4-
ligands, which can be regarded as an eight-connecting node. The
resulting (4,8)-connected net resembles the fluorite structure with
the Schla¨fli symbol of (410·614·84)(45·6)2.21 It is well-known that
fluorite is one of the most important and frequently encountered
structure types in minerals. Although it has been successfully
replicated in several neutral metal–organic nets, what we describe
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Fig. 2 (a) Ball-and-stick and schematic representations of 4-connected
and 8-connected nodes, respectively. (b) Structure showing the complete
connectivity between the 8-connected Co3 clusters and the 4-connected
[MDIP]4- anions (gray and blue balls represent four- and eight-connected
nodes, respectively; the purple lines represent a unit cell).
O7A), two coordinated aqua molecules (O12 and O13) and one m2-
hydroxyl group (O9). The Ni1 and Ni2 centers are bridged through
two carboxylate groups and one m2-hydroxyl group to form a
˚
binuclear unit with a Ni ◊ ◊ ◊ Ni distance of 3.507 A. Interestingly,
the Ni2 units are linked into R- and L- helical chains along
the b-axis through the isophthalate and [HMDIP]3- respectively
(Fig. 3b). There are four carboxylate groups associated with
each Ni2 unit, and each [HMDIP]3- ligand links four Ni2 units
using its four carboxylate groups to allow the formation of a 3D
open framework with elliptical channels viewed along the a-axis
directions. Because the Ni2 units and [HMDIP]3- serve as four-
connected nodes, the resultant framework can be rationalized as
having crb topology with the Schla¨fli symbol of (4·65) (Fig. 3c).22
PLATON analysis showed that the effective free volume of 2 is
30.98% of the crystal volume.
Fig. 1 (a) Coordination environment of the Co(II) ion in 1. Hydrogen
atoms are omitted for clarity. Symmetry codes: A, -x,-y+1,-z+1; B,
x-1/2,-y+1/2,-z+1; C, x-1/2,-y+3/2,-z+1; D, -x+1/2,-y+1,z-1/2.
(b) View of the tri-nuclear cobalt(II) unit surrounded by eight MDIP4-
ligands in 1.
here represents the first example where the structure of fluorite is
perfectly imitated in a magnetic anionic framework.
Structure of [Ni2(HMDIP)(l2-OH)(H2O)3(DMF)]·8H2O (2).
When CoO was replaced by NiO, a fascinating 3D structure of 2
was obtained. As illustrated in Fig. 3a, compound 2 contains two
distinctive nickel atoms, one m2 hydroxyl group, one coordinated
DMF molecule, three coordinated aqua molecules, and one
monoprotonated [HMDIP]3- ligand (Fig. 3a). The Ni1 atom
with a slightly distorted octahedral geometry is coordinated by
six oxygen atoms from three [HMDIP]3- anions (O2, O5C, and
O8A), one coordinated aqua molecule (O11), one m2-hydroxyl
group (O9), and one DMF molecule (O10). Ni2 also adopts a
distorted octahedral coordination geometry, surrounded by six
oxygen atoms from three different [HMDIP]3- (O1, O4B, and
Structure of [Cu3(MDIP)(l2-OH)2(H2O)4]·6.5H2O (3). Com-
pound 3 was obtained under different reaction conditions to
that of 1 and 2. As shown in Fig. 4a, the basic unit contains
three Cu(II) metal centres arranged in linear that are bridged by
one carboxylate group and one m2-hydroxyl group. In the unit,
the Cu1 is five-coordinated with a distorted square-pyramidal
geometry (t ª 0.14),23 where one m2-hydroxyl oxygen atom (O5),
two carboxyl oxygen atoms (O2 and O4c) and one coordinated
water molecule (O6) lie in the basic plane, while the other aqua
ligand (O7) occupies the apical position. The Cu2 is ligated by
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is calculated by PLATON analysis to be 26.14% of the crystal
volume. R- and L-helical chains along the x-axis are formed by the
isophathalic carboxylates between tri-nuclear copper units (Fig.
S2†). If the tri-nuclear units and [MDIP]4- are considered as four-
connected nodes, the resulting network is of the pts topology with
the Schla¨fli symbol of (42·84) (Fig. S3†).24
For 3, one of the most prominent structural characteristics is the
one dimensional channels constituted by Cu3 units and [MDIP]4-
ions (Fig. 4d). Along the c-axis, the Cu3 units with the same
orientation are merely arranged linearly rather than connect with
each other, whereas those with different orientations are joined
together by [MDIP]4- ions to form an open framework. To the
best of our knowledge, such 3D open frameworks constructed by
linear Cu3 units and carboxylate ligands with the above structure
have never been observed prior to this work.25
In a comparison of the structures of 1–3, it is found that the
coordination geometry of the central metal ions has significant
effects on the structures of the resulting complexes. In addition,
different coordination modes of the carboxylate ligand also have
a significant effect on the structures, as evidenced by the fact that
the structure of 1 is significantly different from that of 2 and 3.
In complex 1, H4MDIP carboxylate groups adopt three kinds
of coordination modes, that is, the bis-mono, bis-chelating, and
chelating-mono coordination modes. The mono and bis-mono
coordination modes exist in complexes 2 and 3 (Fig. 5). In 1–
3, the dihedral angles between two aryl rings of H4MDIP are
89.03, 86.95 and 115.01◦ respectively, which are also related to
their coordination mode. In complex 3, the [MDIP]4- with a
higher symmetrical configuration leads to a higher symmetrical
3D framework.
Magnetic properties
The magnetic susceptibilities of complexes 1–3 were measured at
0.1 T field in the temperature rang 2–300 K. Phase purity of the
powder sample of three complexes was confirmed by comparison
of its powder diffraction (XRPD) pattern with that calculated from
the single-crystal study (Fig. S4–S6†). The magnetic susceptibility
of 1 versus temperature is shown in Fig. 6, the cMT value is
9.17 cm3 mol-1 K at 300 K, which is significantly larger than the
spin-only value of 5.63 cm3 mol-1 K calculated for three high-spin
Co(II) ions (S = 3/2, g = 2) due to the unquenched orbital-moment
as a consequence of spin–orbit coupling from single octahedral
Co(II) ions. Upon lowering the temperature, cMT decreases slowly
to a minimum value of 6.42 cm3 mol-1 K at 9 K resulting from the
depopulation of the higher energy Kramers doublets associated
with the high-spin Co(II) single ions.26 When the temperature
continues to decrease from 9 K, the cMT value abruptly increases
abruptly to 7.11 cm3 mol-1 K at 2 K, indicating the presence of
intramolecular ferromagnetic interactions between the Co(II) ions
mediated by the carboxylate bridges. The magnetic susceptibility
above 30 K obeys the Curie–Weiss law with the Weiss constant, q =
-12.53 K, and Curie constant, C = 9.59 cm3 mol-1 K per Co3 unit.
To quantitatively evaluate the magnetic interactions in 1, the
data above 50 K were fitted to the expression of susceptibility
for linear tri-nuclear systems based on the Hamiltonian H =
-2J(S1S2+S2S3). We have assumed that the exchange constant
between the terminal Co(II) ions was zero. And the inter-
trimer interaction (zJ¢) was dealt with by the molecular-field
Fig. 3 (a) Coordination environment of the Ni(II) ion in complex
2. Hydrogen atoms are omitted for clarity. Symmetry codes: A,
-x+1,y+1/2,-z+1/2; B, x-1,-y+1/2,z-1/2; C, x-1,y,z. (b) Schematic
representation of the L- and R- helical chains along y-axis. (c) Topological
view showing the equivalent 3D framework for 2 along x-axis (green balls,
Ni2 dimers; pink balls, 4-connected H4MDIP ligands).
four oxygen atoms (O3B, O3C, O5, and O5A), exhibiting a planar
square geometry. Each tri-nuclear unit is connected to twelve
others through four [MDIP]4- ions to generate a 3D framework
with one-dimensional elliptical channels along the c-axis (Fig. 4b
and Fig. 4c). Without guest molecules, the effective free volume
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Fig. 4 (a) Coordination environment of the Cu(II) ion in 3. Hydrogen atoms are omitted for clarity. Symmetry codes: A, -x,-y+1,-z+1; B, -x+1/2,y,z+1/2;
C, x-1/2,-y+1,-z+1/2. (b) View of the tri-nuclear copper(II) unit and the tri-nuclear unit surrounded by four MDIP4- ligands in 3. (c) The network of 1
with 1D elliptical channels viewed along the z-axis. (d) Connectivity of tri-nuclear units in the z-axis in 3.
approximation.27 The best fit was obtained with values of J =
2.71 cm-1, zJ¢ = 0.35 cm-1, g = 2.59 and R2 = 0.97744. This
result indicates that ferromagnetic coupling interactions exist both
between the adjacent Co(II) sites and between the adjacent trimers,
although the latter is much weaker.
As shown in Fig. 7, for complex 2, at room temperature the
value of cMT is 2.55 cm3 mol-1 K, which is larger than the
expected value of 2.00 cm3 mol-1 K for two magnetically uncoupled
NiII (S = 1) centers. The cMT values gradually increase with
decreasing temperature attesting to the presence of a ferromagnetic
exchange interaction. The cMT versus T plot presents a maximum
(2.71 cm3 mol-1 K) at 9 K and then decreases until a value of
2.21 cm3 mol-1 K at 2 K. The decrease of the cMT values at
Fig. 5 The coordination modes of MDIP ligands in complexes 1–3.
This journal is The Royal Society of Chemistry 2010
low temperature can be due to a zero-field splitting of the S = 2
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Fig. 6 Temperature dependence of the cMT and cM-1 curve for 1. The red
line represents the best fit to the equation in the text. The blue line shows
the Curie–Weiss fitting.
Fig. 8 Temperature dependence of the cMT and cM-1 curve for 3. The red
line represents the best fit to the equation in the text. The blue line shows
the Curie–Weiss fitting.
a value of 2.04 cm3 mol-1 K at 20 K. This behavior is indicative
of strong ferromagnetic coupling between the adjacent Cu(II) in
the tri-nuclear units. Below 20 K, cMT decreases rapidly down to
1.26 cm3 mol-1 K, which is most likely due to zero-field splitting
within the quartet ground state. The occurrence of inter-trimer
antiferromagnetic interactions may also be operative at very low
temperatures. A fitting of the data above 30 K using the Curie–
Weiss law gives the Weiss constant, q = 33.36 K, and Curie
constant, C = 6.64 cm3 mol-1 K per Cu3 unit.
The magnetic analysis was carried out using the susceptibility
equation based on the spin Hamiltonian, H = -2J(S1S2+S2S3)
- 2jS1S3, assuming that the exchange integrals between the
neighbouring copper ions are identical (J12 = J23 = J) and j
describes the integral between the terminal copper ions within
the tri-nuclear unit. The magnetic susceptibility for the linear
tri-nuclear copper(II) system may be expressed by eqn (3).30 To
take into account the inter-trimer super-exchange coupling, the
magnetic susceptibility can be corrected by the molecular field
approximation eqn (4).
Fig. 7 Temperature dependence of the cMT and cM-1 curve for 2. The red
line represents the best fit to the equation in the text. The blue line shows
the Curie–Weiss fitting.
ground spin state. The data above 30 K follows the Curie–Weiss
law with the Weiss constant, q = 2.72 K, and Curie constant, C =
2.54 cm3 mol-1 K per Ni2 dimer.
It is possible to represent the intradimer magnetic exchange
interaction (J) by two equivalent S = 1 ions using eqn (1) by
means of the Hamiltonian H = -2JS1S2.28
Ng2b exp(−2J /kT)+10exp(J /kT)+exp(−2 j/kT)
2
ctrimer
=
×
4kT
exp(−2J /kT)+2exp(J /kT)+exp(−2 j/kT)
(3)
ctrimer
cm =
(4)
2
2Ng2b
exp(J /kT)+5exp(3J /kT)
1+3exp(J /kT)+5exp(3J /kT)
2
2
′
1− ctrimer 2zJ /Ng b
(1)
cdimer
=
×
kT
A good fit with the experimental data was obtained for J =
20.94 cm-1, j = -7.22 cm-1, zJ¢ = -0.41 cm-1, g = 2.38 and R2 =
0.96181. The results show that the predominant ferromagnetic
coupling is due to the interaction between neighbouring copper
ions. A smaller antiferromagnetic contribution results from inter-
action between the terminal copper ions. The negative zJ¢ value
suggests weak antiferromagnetic coupling between the trimers.
cdimer
cm =
(2)
2
2
′
1− cdimer 2zJ /Ng b
Considering the molecular field approach with zJ¢ as the
exchange coupling between Ni2 dimers, we can fit our experimental
data with eqn (2). The best fit gives J = 1.98 cm-1, zJ¢ = -0.26 cm-1,
g = 2.27 with R2 = 0.95699. The positive sign of the J factor verifies
the ferromagnetic nature of the exchange.
Thermal analysis
The variable-temperature magnetic susceptibility of 3 is shown
in Fig. 8, the cMT value at 300 K is 1.65 cm3 mol-1 K, which
lies in the usual range expected for trimeric Cu(II) ions with g
> 2.29 Upon cooling of the sample, cMT increases and reaches
To characterize the thermal stabilities of compounds 1–3, their
thermal behaviors were investigated by TGA under a nitrogen
◦
atmosphere with a heating rate of 10 C min-1 (Fig. S7†). For
compound 1, the weight loss corresponding to the release of two
9128 | Dalton Trans., 2010, 39, 9123–9130
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water molecules and one DMF molecule is observed from 105
to 390 ◦C (obsd 10.32%, calcd 10.37%). The destruction of the
frameworks occurs from 420 to 480 ◦C, leading to the formation
of CoO as the residue (obsd 22.22◦%, calcd 21.58%). For 2, the
weight loss in the range of 40–105 C is attributed to the release
of eight guest water molecules (obsd 21.03%, calcd 19.28%). The
destruction of the frameworks occurs at ca. 385 ◦C with a residue
of NiO (obsd 20.12%, calcd 20.00%). Compound 3 lost its guest
water molecules from 40 to 150 ◦C (obsd 15.34%, calcd 15.52%).
The compound was stable up to 260 ◦C, and the removal of
organic components occurs from 260 to 430 ◦C. The remaining
weight corresponds to the formation of CuO (obsd 33.78%, calcd
31.67%).
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Fe´rey, Angew. Chem., Int. Ed., 2005, 44, 6488; (b) P.-K. Chen, Y.-X. Che,
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Conclusions
We have successfully synthesized three new Co(II), Ni(II) and
Cu(II) coordination polymers using the semi-rigid ‘V’-shaped
H4MDIP ligand. The results reveal that the distinct structures
of the final products are caused by different coordination envi-
ronments around central metal ions and the coordination modes
of the carboxylate ligand (H4MDIP). Magnetic susceptibility
measurements reveal dominant ferromagnetic interactions for the
three complexes. The three compounds not only show an aesthetic
diversity of coordinative chemistry, but also, for example, can be
used for the design of magnetic materials. Our future work will
focus on the synthesis of new functional coordination polymers
by using other paramagnetic metals and the H4MDIP ligand.
Acknowledgements
10 (a) Q.-R. Fang, G.-S. Zhu, M. Xue, J.-Y. Sun, F.-X. Sun and S.-L.
Qiu, Inorg. Chem., 2006, 45, 3582; (b) A. Banerjee, P. Mahata and S.
Natarajan, Eur. J. Inorg. Chem., 2008, 3501.
11 (a) X.-M. Chen and G.-F. Liu, Chem.–Eur. J., 2002, 8, 4811; (b) P.
Vishweshwar, A. Nangia and V. M. Lynch, Cryst. Growth Des., 2003, 3,
783; (c) S. L. Childs, L. J. Chyall, J. T. Dunlap, V. N. Smolenskaya, B. C.
Stahly and G. P. Stahly, J. Am. Chem. Soc., 2004, 126, 13335; (d) B. F.
Abrahams, T. A. Hudson and R. Robson, J. Am. Chem. Soc., 2004,
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Des., 2005, 5, 1825.
The authors are grateful for financial aid from the National
Natural Science Foundation of China (Grant No. 20631040, and
20771099) and the MOST of China (Grant No. 2006CB601103,
2006DFA42610).
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