Synthesis, structures, and magnetism of copper(II) and manganese(II) coordination polymers with azide and pyridylbenzoates

Article abstract of DOI:10.1021/ic2008842

Three transition-metal coordination polymers with azide and/or carboxylate bridges have been synthesized from 4-(3-pyridyl)benzoic acid (4,3-Hpybz) and 4-(4-pyridyl)benzoic acid (4,4-Hpybz) and characterized by X-ray crystallography and magnetic measurements. Compound 1, [Cu(4,3-pybz)(N₃)] _n, consists of 2D coordination networks in which the uniform chains with (μ-EO-N₃)(μ-COO) double bridges are cross-linked by the 4,3-pybz ligands. Compound 2, [Cu₂(4,4-pybz)₃(N ₃)]_n?3nH₂O, consists of 2-fold interpenetrated 3D coordination networks with the α-Po topology, in which the six-connected dinuclear motifs with mixed (μ-EO-N₃)(μ-COO) ₂ (EO = end-on) triple bridges are linked by the 4,4-pybz spacers. Compound 3, [Mn(4,4-pybz)(N₃)(H₂O)₂] _n, contains 2D manganese(II) coordination networks in which the chains with single μ-EE-N₃ bridges (EE = end-to-end) are interlinked by the 4,4-pybz ligands, and the structure also features a 2D hydrogen-bonded network in which Mn^II ions are linked by double triatomic bridges, (μ-EE-N₃)(O-H???N) and (O-H???O)₂. Magnetic studies indicated that the mixed azide and carboxylate bridges in 1 and 2 induce ferromagnetic coupling between Cu^II ions and that 3 features antiferromagnetic coupling through the EE-azide bridge. In addition, compound 1 exhibits antiferromagnetic ordering below 6.2 K and behaves as a field-induced metamagnet. A magnetostructural survey indicates a general trend that the ferromagnetic coupling through the mixed bridges decreases as the Cu-N-Cu angle increases.

Full text of DOI:10.1021/ic2008842

ARTICLE
pubs.acs.org/IC
Synthesis, Structures, and Magnetism of Copper(II) and Manganese(II)
Coordination Polymers with Azide and Pyridylbenzoates
Xiu-Mei Zhang,†,‡ Yan-Qin Wang,† You Song,§ and En-Qing Gao*,†
†Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University,
Shanghai 200062, China
‡School of Chemistry and Materials Science, Huaibei Normal University, Huaibei, Anhui 235000, China
§State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University,
Nanjing 210093, China
S Supporting Information
b
ABSTRACT: Three transition-metal coordination polymers with
azide and/or carboxylate bridges have been synthesized from 4-(3-
pyridyl)benzoic acid (4,3-Hpybz) and 4-(4-pyridyl)benzoic acid (4,4-
Hpybz) and characterized by X-ray crystallography and magnetic
measurements. Compound 1, [Cu(4,3-pybz)(N3)]n, consists of 2D
coordination networks in which the uniform chains with (μ-EO-
N3)(μ-COO) double bridges are cross-linked by the 4,3-pybz ligands.
Compound 2, [Cu2(4,4-pybz)3(N3)]n 3nH2O, consists of 2-fold
3
interpenetrated 3D coordination networks with the R-Po topology,
in which the six-connected dinuclear motifs with mixed (μ-EO-
N3)(μ-COO)2 (EO = end-on) triple bridges are linked by the 4,4-
pybz spacers. Compound 3, [Mn(4,4-pybz)(N3)(H2O)2]n, contains 2D manganese(II) coordination networks in which the chains
with single μ-EE-N3 bridges (EE = end-to-end) are interlinked by the 4,4-pybz ligands, and the structure also features a 2D
hydrogen-bonded network in which MnII ions are linked by double triatomic bridges, (μ-EE-N3)(OꢀH N) and (OꢀH O)2.
3 3 3
3 3 3
Magnetic studies indicated that the mixed azide and carboxylate bridges in 1 and 2 induce ferromagnetic coupling between CuII ions
and that 3 features antiferromagnetic coupling through the EE-azide bridge. In addition, compound 1 exhibits antiferromagnetic
ordering below 6.2 K and behaves as a field-induced metamagnet. A magnetostructural survey indicates a general trend that the
ferromagnetic coupling through the mixed bridges decreases as the CuꢀNꢀCu angle increases.
’ INTRODUCTION
or coordination polymers with diverse topologies and magnetic
properties.3,6ꢀ13
The research of molecular magnetic systems has been of
considerable interest for decades, aimed at elucidating funda-
mental magnetic phenomena, unveiling magnetostructural cor-
relations, and constructing new magnetic materials with potential
applications.1,2 Coordination chemistry has been the most
powerful tool to access such systems, and the general approach
is to use short bridging groups to connect paramagnetic metal
centers and to transmit magnetic coupling. Among the most
frequently used bridging groups in this context, carboxylate and
azide have exceptionally rich coordination chemistry and mag-
netochemistry, capable of linking metal ions in various modes and
transmitting magneticexchangeofdifferent nature and magnitude.3
The rich chemistry challenges the designed assembly,4 which is
always pursued as an appealing approach to targeted and tunable
structures or properties, but has offered great opportunities for
serendipitous assembly, which is always an important approach
to new structures or new properties.5 To evoke the rich chemistry or
sometimes to gain some control, various auxiliary organic ligands
for azide and various backbones for carboxylate ligands have been
introduced, leading to a large number of polynuclear aggregates
Using azide and carboxylate as cobridges is an interesting
approach to magnetic systems, but the cobridging of the two
anionic groups may be impeded by the competition in coordina-
tion and charge balance. A limited number of cobridging systems
have been synthesized from mono/dicarboxylate ligands [RCOOꢀ/
R(COOꢀ)2] (R = H, methyl, ethyl, and phenylene).14ꢀ16 Recently,
we have demonstrated that the zwitterionic mono/dicarboxylate
ligands bearing self-compensated positive (pyridinium) and
negative (carboxylate) charges can readily collaborate with azide
to generate 1D, or sometimes 0D, 2D, or even 3D, magnetic motifs
with simultaneous azide and carboxylate bridges, with interesting
magnetic properties such as ferromagnetic coupling, solvent-
modulated metamagnetism, and single-chain magnetism.17,18
The pyridylcarboxylate bifunctional ligands such as pyridylcar-
boxylates and pyridylacrylates have also led to some cobridging
systems, with various structures and magnetic properties.19,20 As
Received: April 27, 2011
Published: July 06, 2011
r
2011 American Chemical Society
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|

Inorganic Chemistry
ARTICLE
an extension of the study, we report in this paper three co-
ordination polymers derived from 4-(3-pyridyl)benzoate (4,3-pybz)
and 4-(4-pyridyl)benzoate (4,4-pybz), [Cu(4,3-pybz)(N3)]n
Table 1. Crystal Data and Structure Refinement for Com-
pounds 1ꢀ3
1
2
3
(1), [Cu2(4,4-pybz)3(N3)]n 3nH2O (2), and [Mn(4,4-pybz)-
3
(N3)(H2O)2]n (3). All of these structures are different from
those with pyridylcarboxylates. In 1, the copper(II) chains with
(μ-EO-N3)(μ-COO) double bridges (EO = end-on) are con-
nected into 2D layers by the 4,3-pybz spacers. In 2, the novel
dicopper motifs with (μ-EO-N3)(μ-COO)2 triple bridges are
linked by 4,4-pybz to generate 3D frameworks with 2-fold
interpenetration. Compound 3 consists of 2D coordination
networks in which the manganese(II) chains with single μ-EE-
N3 bridges (EE = end-to-end) are linked by 4,4-pybz ligands, and
formula
Mr
CuC12H8N4O2 Cu2C36H30N6O9 MnC12H12N4O4
303.76
817.76
331.20
cryst syst
space group
a [Å]
monoclinic
P21
monoclinic
P21/c
monoclinic
P21/c
8.5221(6)
6.4754(4)
11.5083(8)
108.673(2)
601.64(7)
2
15.2793(12)
19.3066(16)
20.7718(16)
99.010(3)
6051.9(8)
4
11.3620(3)
15.3393(4)
7.5356(2)
90.0090(10)
1313.34(6)
4
b [Å]
c [Å]
β [deg]
V [Å3]
Z
the structure is reinforced by the OꢀH N and OꢀH
O
3 3 3
3 3 3
triatomic bridges between MnII ions. Magnetic studies indicated
that the mixed bridges in 1 and 2 induce ferromagnetic coupling
between CuII ions and that 3 features antiferromagnetic coupling
along the EE-azide-bridged chain. In addition, 1 behaves as a
metamagnet. A magnetostructural survey indicates a general
trend that the ferromagnetic coupling through the mixed bridges
decreases as the CuꢀNꢀCu angle increases.
F
calcd [g cmꢀ3
μ [mmꢀ1
]
1.677
0.897
1.675
]
1.817
0.740
1.028
no. of unique reflns 2744
13 054
3189
Rint
0.0383
0.0255
0.0254
R1 [I > 2σ(I)]
wR2 (all data)
0.0470
0.1126
0.0485
0.0264
0.1457
0.0732
’ EXPERIMENTAL SECTION
Materials and Physical Measurements. All of the solvents and
reagents including 4,3-Hpybz and 4,4-Hpybz were purchased commer-
cially (Sinopharm and Alfa Aesar) and were used as received. IR spectra
were recorded on a Nexus 670 FT-IR spectrometer using KBr pellets.
Elemental analysis was carried out on an Elementar Vario El III
elemental analyzer. Temperature- and field-dependent magnetic mea-
surements were carried out on a Quantum Design SQUID MPMS-5
magnetometer. Diamagnetic corrections were made with Pascal’s constants.
Caution! Although not encountered in our experiments, azide compounds
of metal ions are potentially explosive. Only a small amount of the materials
should be prepared, and it should be handled with care.
[Cu(4,3-pybz)(N3)]n (1). In a test tube, a solution of 4,3-Hpybz
(0.010 g, 0.05 mmol) and NaN3 (0.013 g, 0.2 mmol) in water (3 mL)
was layered carefully with water/ethanol (1:1, 4 mL) and then an ethanol
solution (3 mL) of Cu(Ac)2 H2O (0.013 g, 0.05 mmol). Slow diffusion
3
at room temperature yielded green crystals of 1 in 2 weeks. Yield: 55%
based on copper. Elem anal. Calcd for C12H8O2N4Cu: C, 47.45; H, 2.65;
N, 18.44. Found: C, 47.58; H, 2.93; N, 18.87. Main IR bands (KBr, cmꢀ1):
2056(s) [ν(N3)], 1597(m) [νas(COO)], 1544(m), 1376(s) [νs(COO)],
1266(w).
[Cu2(4,4-pybz)3(N3)]n 3nH2O (2). In a test tube, a dimethyl
3
sulfoxide (DMSO) solution (3 mL) of 4,4-Hpybz (0.010 g, 0.05 mmol)
and NaN3 (0.013 g, 0.2 mmol) was layered carefully with DMSO/methanol
(2:1, 3 mL) and then a methanol solution (3 mL) of Cu(ClO4)2 6H2O
3
(0.013 g, 0.05 mmol). Slow diffusion at room temperature yielded green
crystals of 2 in 1 week. Yield: 60% based on copper. Elem anal. Calcd for
C36H30O9N6Cu2: C, 52.88; H, 3.70; N, 10.28. Found: C, 52.89; H, 3.43; N,
9.99. Main IR bands (KBr, cmꢀ1): 2081(m) [ν(N3)], 1608(s)
[νas(COO)], 1564(m), 1400(s) [νs(COO)], 1373(m).
Figure 1. (a) Local coordination environments in compound 1. Hydrogen
atoms are omitted for clarity. (b) 2D network formed by the 4,3-pybz
ligands connecting the copperꢀazideꢀcarboxylate chains.
[Mn(4,4-pybz)(N3)(H2O)2]n (3). A mixture of MnCl2 4H2O
3
(0.020 g, 0.1 mmol), NaN3 (0.052 g, 0.8 mmol), and 4,4-Hpybz
(0.005 g, 0.025 mmol) in DMSO (1 mL), methanol (1 mL), and
distilled water (0.5 mL) was stirred for 30 min in air and then heated in a
23 mL Teflon-lined autoclave at 70 ꢀC for 5 days. After the mixture was
slowly cooled to room temperature, yellow block crystals of 3 were collected.
Yield: 22% based on manganese. Elem anal. Calcd for C12H12O4N4Mn: C,
43.52; H, 3.65; N, 16.92. Found: C, 43.85; H, 3.91; N, 16.93. Main IR bands
(KBr, cmꢀ1): 2089(m) [ν(N3)], 2063(s) [ν(N3)], 1607(s) [νas(COO)],
1558(m), 1381(s) [νs(COO)], 1009(w).
X-ray Crystallography. Diffraction data for 1ꢀ3 were collected at
296 K on a Bruker Apex II CCD area detector equipped with graphite-
monochromated Mo KR radiation (λ = 0.710 73 Å). Empirical absorp-
tion corrections were applied using the SADABS program.21 The struc-
tures were solved by direct methods and refined by a full-matrix least-
squares method on F2, with all non-hydrogen atoms refined with
anisotropic thermal parameters.22 All of hydrogen atoms attached to
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ARTICLE
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Compound 1a
Cu1ꢀO1
Cu1ꢀN2
Cu1ꢀN1B
1.962(2)
1.985(3)
2.320(3)
Cu1ꢀO2A
Cu1ꢀN2A
1.963(2)
1.994(3)
O1ꢀCu1ꢀO2A
O2AꢀCu1ꢀN2
O2AꢀCu1ꢀN2A
O1ꢀCu1ꢀN1B
N2ꢀCu1ꢀN1B
Cu1ꢀN2ꢀCu1D
166.55(11)
88.79(10)
89.61(11)
92.65(10)
93.93(10)
109.40(12)
O1ꢀCu1ꢀN2
90.85(11)
88.83(11)
171.75(10)
100.79(10)
94.31(11)
O1ꢀCu1ꢀN2A
N2ꢀCu1ꢀN2A
O2AꢀCu1ꢀN1B
N2AꢀCu1ꢀN1B
a Symmetry codes: A, ꢀx + 1, y ꢀ /2, ꢀz + 2; B, ꢀx + 1, y + 1/2, ꢀz + 1;
1
1
1
C, ꢀx + 1, y ꢀ /2, ꢀz + 1; D, ꢀx + 1, y ꢀ /2, ꢀz + 2.
carbon atoms were placed in calculated positions and refined using the
riding model. The water hydrogen atoms in 3 were located from difference
maps. In 2, the uncoordinated guest molecules could not be modeled
because of the heavy disorder and the limited quality of the data set. The
final refinements were carried out using the data obtained by the SQUEEZE
routine in the PLATON software package.23 According to elemental
analytical data, the guest molecules were proposed to be H2O. Some 4,
4-pybz ligands are also disordered. A summary of the crystallographic data,
data collection, and refinement parameters is provided in Table 1.
Figure 2. Coordination environments of CuII ions in compound 2 (30%
probability thermal ellipsoids). For clarity, all hydrogen atoms are omitted.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Compound 2a
Cu1ꢀO6
Cu1ꢀN2A
Cu1ꢀN1B
Cu2ꢀO4
Cu2ꢀO2
1.9190(17)
2.032(3)
2.188(2)
1.955(7)
2.174(2)
Cu1ꢀO1
Cu1ꢀN3
Cu2ꢀN3
Cu2ꢀN6C
Cu2ꢀO5
1.9469(17)
2.039(3)
1.953(2)
1.985(2)
2.195(2)
’ RESULTS AND DISCUSSION
Description of the Structures. Compound 1. This compound
contains a 2D coordination network in which 1D [Cu(N3)(COO)]n
chains are linked by the organic 4,3-pybz ligands (Figure 1a).
Selected bond lengths and angles are listed in Table 2. The
asymmetric unit consists of one metal ion, one 4,3-pybz, and one
azide ion. The CuII ion exhibits a distorted square-pyramidal geome-
try, for which the basal plane consists of two carboxylate oxygen
atoms and two azide nitrogen atoms with the apical position
occupied by a pyridine nitrogen atom. The apical CuꢀN distance
[2.320(3) Å] is significantly longer than the basal CuꢀN/O
distances [1.962(2)ꢀ1.994(3) Å]. The distortion parameter τ,
defined as (ϕ1 ꢀ ϕ2)/60 (ϕ1 and ϕ2 are the two largest bond
angles of the coordination sphere) by Addison et. al.,24 is 0.07,
suggesting a basically square-pyramidal coordination geometry (τ =
0 and 1 for perfect square and trigonal bipyramids, respectively).
The basal atoms deviate from their mean plane by less than 0.053(5)
Å, and Cu1 is out of the mean basal plane by 0.1916(6) Å. Adjacent
CuII ions are doubly linked by an azide bridge in the EO mode and a
carboxylate bridge in the synꢀsyn mode to generate a uniform chain
running along the b direction (Figure 1b). It is notable from the
viewpoint of magnetic relevance that both bridges adopt the
basalꢀbasal disposition (the donor atoms of the bridges are at basal
O6ꢀCu1ꢀO1
O1ꢀCu1ꢀN2A
O1ꢀCu1ꢀN3
O6ꢀCu1ꢀN1B
N2AꢀCu1ꢀN1B
N3ꢀCu2ꢀO4
O4ꢀCu2ꢀN6C
O4ꢀCu2ꢀO2
N3ꢀCu2ꢀO5
N6CꢀCu2ꢀO5
Cu1ꢀN3ꢀCu2
171.30(8)
91.32(10)
88.61(9)
95.87(9)
98.31(11)
93.72(18)
93.60(18)
144.1(2)
86.64(9)
91.14(9)
101.11(11)
O6ꢀCu1ꢀN2A
O6ꢀCu1ꢀN3
N2AꢀCu1ꢀN3
O1ꢀCu1ꢀN1B
N3ꢀCu1ꢀN1B
N3ꢀCu2ꢀN6C
N3ꢀCu2ꢀO2
N6CꢀCu2ꢀO2
O4ꢀCu2ꢀO5
O2ꢀCu2ꢀO5
89.72(10)
88.11(9)
164.62(10)
92.53(9)
97.05(10)
172.68(11)
88.38(9)
85.82(9)
105.9(2)
110.04(8)
a Symmetry codes: A, x ꢀ 1, y, z; B, x, ꢀy + 1/2, z + 1/2; C, x, ꢀy + 3/2,
1
1
z ꢀ /2; D, x, ꢀy + 1/2, z ꢀ /2; E, x + 1, y, z; F, x, ꢀy + 3/2, z + 1/2.
Compound 2. According to X-ray crystallographic analyses,
the structure is a 3D metalꢀorganic framework based on di-
nuclear units with mixed azide and carboxylate bridges. The unit
structure is shown in Figure 2, and selected bond lengths and
angles are listed in Table 3. There are two CuII ions in the
asymmetric unit. The Cu1 ion resides in a distorted square-
pyramidal environment: the basal plane defined by two carbox-
ylate oxygen atoms (O1 and O6), an azide nitrogen atom (N3),
and a pyridyl nitrogen atom (N2A). The apical position is
occupied by another pyridyl nitrogen atom (N1B), with the
apical CuꢀN distance [ca. 2.188(2) Å] being longer than the
basal CuꢀO/N distances [1.919(2)ꢀ2.039(3) Å]. The basal
atoms deviate from their mean plane by less than 0.098(3) Å, and
Cu1 is out of the mean basal plane by 0.186(3) Å. The trigonality
index for this Cu site has been calculated to be τ = 0.11, suggest-
ing a square-pyramidal geometry with very slight distortion.
Differently, the coordination surrounding of Cu2 is intermediate
positions around metal ions). The Cu Cu distances spanned by
3 3 3
the double bridge are 3.248(1) Å, and the CuꢀNꢀCu angle is
109.4(1)ꢀ.
The 4,3-pybz ligands bind metal ions in the μ3-tridentate
coordination mode via the pyridyl and synꢀsyn carboxylate
groups and thus interlink the [Cu(N3)(COO)]n chains to generate
a 2D layer along the bc plane (Figure 1b). The nearest interchain
Cu Cu distance is 11.508(1) Å, spanned by the ligand. The layers
3 3 3
are packed with weak interlayer hydrogen bonds, which involve
CꢀH groups from one layer and azide nitrogen atoms from another
layer (see the Supporting Information, Figure S1). The shortest
interlayer Cu Cu distances are 8.522(1) Å.
3 3 3
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Inorganic Chemistry
ARTICLE
Figure 3. (a) Single pcu net based on dinuclear units in 2. (b) 2-fold
interpenetration of the nets.
between square-pyramidal and trigonal-bipyramidal, with τ =
0.48. For a square-pyramidal description, the basal plane, similar
to that for Cu1, consists of two carboxylate oxygen atoms (O2
and O4), an azide nitrogen atom (N3), and a pyridyl nitrogen
atom (N6C), but the apical position is completed by a third
carboxylate oxygen atom (O5). The axial Cu2ꢀO5 distance
[2.195(2) Å] is slightly longer than the basal Cu2ꢀO2 distance
[2.174(2) Å] and significantly elongated compared with the
other basal CuꢀO/N distances [1.953(2)ꢀ1.985(2) Å]. For the
trigonal-bipyramidal description, the equatorial plane is defined
by three carboxylate oxygen atoms, with two axial nitrogen atoms
from azide and pyridyl. We noted that a fourth carboxylate
oxygen atom (O3) is at 2.568(2) Å from Cu2, suggesting weak
coordination. If this is included, the O4ꢀCꢀO3 carboxylate
binds Cu2 in a highly asymmetric chelating fashion with a small
bit angle of 54.3(3)ꢀ, and the geometry around Cu2 may be
described as a highly distorted octahedral.
Cu1 and Cu2 is triply bridged by an EO azide and two synꢀsyn
carboxylates to generate a dinuclear [Cu2(N3)(COO)2] motif.
The Cu Cu distance is 3.083(3) Å, with CuꢀNꢀCu =
3 3 3
101.1(1)ꢀ. Noticeably, both the distance and the bridging angle
are the smallest of the known copper(II) complexes with mixed
azide and carboxylate bridges (see below). Assuming a square-
pyramidal geometry for both metal ions, the basal planes of Cu1
and Cu2 are almost orthogonal to each other with a dihedral
angle of 89.33(7)ꢀ. The azide and O1ꢀCꢀO2 bridges are in the
basalꢀbasal fashion, while the O5ꢀCꢀO6 carboxylate bridge
adopts the apicalꢀbasal disposition (O5 at the apical position of
Cu2 and O6 at the basal position of Cu1). These features are
pertinent to the magnetic properties.
Figure 4. Structure of 3: (a) a chain with azide and hydrogen-bonding
bridges; (b) a top view of the 2D layer formed by 4,4-pybz interlinking
the chains; (c) a 2D sheet through hydrogen bonds. The purple lines
highlight the 44 net topology. Parameters for hydrogen bonds:
O4ꢀH4B O2 = 164.7(2)ꢀ, H O = 1.79(2) Å, and O4 O2 =
3 3 3
3 3 3
3 3 3
2.605(2) Å; O4ꢀH4C N2 (x, 1.5 ꢀ y, 0.5 + z) = 159.6(2)ꢀ, H
3 3 3
3 3 3
N = 2.08(2) Å, and O4 N2 = 2.870(2) Å.
3 3 3
nets is 7.489(6) Å. The cavities left in the 2-fold interpenetrated
structure are occupied by water molecules.
Compound 3. Single-crystal X-ray analyses revealed that the
structure of compound 3 contains 2D coordination layers in
which 1D [Mn(EE-N3)]n chains are interlinked by the 4,4-pybz
ligands (Figure 4a). Selected bond distances and angles are given
in Table 4. The unique Mn1 ion assumes a distorted octahedral
geometry completed by two azide nitrogen atoms (N2 and N4A), a
carboxylate oxygen atom (O1), a pyridyl nitrogen atom (N1B),
and two water molecules (O3 and O4). The average bond lengths
are 2.232(1) Å for MnꢀN and 2.200(1) Å for MnꢀO. The bond
valence sum25 is 1.999, indicating the MnII oxidation state (this is
also supported by magnetic data; see below). Adjacent metal ions
are bridged by single end-to-end (EE) azide ligands, with a
The dimeric unit is furnished by six 4,4-pybz ligands, which
radiate in octahedral directions and adopt μ3- or μ2-tridentate
coordination modes (with bridging or asymmetrically chelating
carboxylate groups, respectively). Thus, the units serve as six-
connecting octahedral secondary building units to yield a 3D
metalꢀorganic framework, which has the topology of the
primitive cubic (pcu, or R-Po) net (Figure 3a). The shortest
interdimeric Cu Cu distances along the three independent
3 3 3
4,4-pybz ligands are 13.065(4), 13.144(4), and 13.160(1) Å. The
long spacer between the dimeric nodes results in large open
cavities within a single net, which is partially filled via 2-fold
interpenetration (Figure 3b). Weak hydrogen bonds are ob-
served between two sets of interpenetrating structures, which
involve a pyridine CꢀH group from one set and the carboxylate
O3 atom from the other set (Figure S2 in the Supporting
Mn Mn distance of 5.338(1) Å, to generate a uniform chain
3 3 3
along the c direction, with a zigzag arrangement of manganese
ions. Coordination of the azide bridge is asymmetric, as shown by
Mn1ꢀN2ꢀN3 = 130.1(1)ꢀ and Mn1AꢀN4ꢀN3 = 117.8(1)ꢀ.
Information). The shortest Cu Cu distance between the two
3 3 3
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Inorganic Chemistry
ARTICLE
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
Compound 3a
Mn1ꢀO1
Mn1ꢀN4A
Mn1ꢀN2
2.1572(10)
2.2168(14)
2.2455(14)
Mn1ꢀO3
Mn1ꢀN1B
Mn1ꢀO4
2.1753(12)
2.2341(12)
2.2682(11)
O1ꢀMn1ꢀO3
O3ꢀMn1ꢀN4A
O3ꢀMn1ꢀN1B
O1ꢀMn1ꢀN2
N4AꢀMn1ꢀN2
O1ꢀMn1ꢀO4
N4AꢀMn1ꢀO4
N2ꢀMn1ꢀO4
87.63(4)
99.64(5)
90.97(5)
91.40(5)
87.47(5)
90.60(4)
176.19(5)
89.49(5)
O1ꢀMn1ꢀN4A
O1ꢀMn1ꢀN1B
N4AꢀMn1ꢀN1B
O3ꢀMn1ꢀN2
N1BꢀMn1ꢀN2
O3ꢀMn1ꢀO4
N1BꢀMn1ꢀO4
87.17(5)
178.57(4)
93.32(5)
172.76(5)
89.96(5)
83.35(4)
88.98(4)
Figure 5. Temperature dependence of χT and χ for 1 under 1 kOe. The
solid lines represent the best fit to the appropriate model (see the text).
a Symmetry codes: A, x, ꢀy + 3/2, z ꢀ /2; B, x ꢀ 1, y, z + 1; C, x + 1, y,
1
z ꢀ 1; D, x, ꢀy + 3/2, z + 1/2.
CurieꢀWeiss law with C = 0.44 cm3 K molꢀ1 and θ = 44.0 K.
The positive θ value suggests the presence of dominant ferro-
magnetic coupling between CuII ions.
The MnꢀN3ꢀMn torsion angle, defined by the dihedral angle
between the Mn1ꢀN2ꢀN3ꢀN4 and Mn1AꢀN4ꢀN3ꢀN2
planes, is 74.5(1)ꢀ, defining a gauche conformation for the Mnꢀ
N3ꢀMn bridging moiety.
Magnetically, the system can be treated as a uniform chain in
which magnetic exchange is mediated through the (COO)(N3)
double bridge. The susceptibility expression proposed by Baker
et al. for Heisenberg ferromagnetic S = 1/2 chains (eq 1)26 and
the molecular-field approximation accounting for interchain
interactions (eq 2)27 were used for magnetic analysis with A =
1 + 5.7979916x + 16.902653x2 + 29.376885x3 + 29.832959x4 +
The 4,4-pybz ligand with monodentate carboxylate and pyridyl
groups interlinks the [Mn(EE-N3)]n chains into a 2D network
(Figure 4b). The zigzag chains are aligned and linked in a
shoulder-by-shoulder fashion so that the 2D network looks like
a bilayer structure as revealed by a side view shown in Figure S3 in
the Supporting Information. The ligand separates the manganese
14.036918x5 and B = 1 + 2.7979916x + 7.008678x2
+
8.6538644x3 + 4.5743114x4 and where x = J/2kT based on the
spin Hamiltonian H = ꢀJ∑SiSi+1
ions by 13.635(6) Å, while the shortest interchain Mn Mn
distance within the layer is 11.362(1) Å.
The layers are packed in parallel into the 3D structure. Two
sets of hydrogen bonds are formed with coordinated water
molecules as donors (Figure 4c). One set is along the azide-
3 3 3
.
ꢀ ꢁ
2=3
Ng2β2
4kT
A
χchain
¼
ð1Þ
ð2Þ
B
bridged chain, involving the O4 water molecule. The O4ꢀH O2
3 3 3
interaction stabilizes the monodentate coordination of the carbo-
xylate group by generating a six-membered ring, while the
xchain
χ ¼
1 ꢀ ðzJ0xchain=Ng2β2Þ
O4ꢀH N2 interaction reinforces the chain structure by
3 3 3
providing a triatomic hydrogen-bonding bridge between neigh-
boring MnII ions. The other set is between the azide-bridged
chains from different layers, involving the O3 water molecules.
The intra- and interchain hydrogen bonds collaborate with the
azide coordinative bridges to arrange the manganese spheres into
a square-grid-like 2D sheet along the bc plane, in which manga-
The experimental susceptibility data above 10 K have been best
fitted by the above expressions with best-fit parameters J =
63.9 cmꢀ1, g = 2.06, and zJ0 = ꢀ2.31 cmꢀ1 (zJ0 describes the
interchain antiferromagnetic interaction). The positive J value
confirms the ferromagnetic coupling through the (COO)(N3)
double bridge.
nese atoms are linked by triatomic NꢀNꢀN and OꢀH O/N
3 3 3
The small negative zJ0 value indicates the presence of inter-
chain antiferromagnetic interactions, consistent with the drop
of the χT product at low temperature. The drop of χ at further
lower temperature may indicate the occurrence of long-range anti-
ferromagnetic ordering. To further investigate the low-temperature
behavior, the field-cooled (FC) magnetizations under different
fields were measured and are shown in Figure 6a. At 5.0 kOe, the
M versus T curves display a maximum at 5.2 K, consistent with
the antiferromagnetic ordering. As the field is lifted, the max-
imum shifts toward lower temperatures, becomes less prominent,
and finally disappears at a high field of 9.0 kOe. The FC behaviors
are characteristic of field-induced metamagnetism,28 with the
disappearance of the maximum indicating that the interchain
antiferromagnetic ordering is broken up by the field.
bridges. The Mn Mn distance spanned by the (NꢀNꢀN)-
3 3 3
(O4ꢀH N2) bridges is 5.338(1) Å, and those by the
3 3 3
3 3 3
(O3ꢀH O4)2 and (O3ꢀH O1)2 bridges are 6.105(1)
3 3 3
and 5.259(1) Å, respectively. It is noted that the last distance
associated with double hydrogen bonds is even shorter than that
spanned by the coordinative azide bridge. Considering this
hydrogen-bonded layer with short metal-to-metal distances,
the whole structure of 3 may be described as a layer-pillared
3D network, with the 4,4-pybz ligands as pillars (Figure S4 in the
Supporting Information).
Magnetic Properties. Complex 1. The susceptibility (χ) of
compound 1 was measured under 1 kOe in the 2ꢀ300 K range
(Figure 5). The χT value per CuII at room temperature is about
0.519 emu K molꢀ1, higher than the value expected for a magne-
tically isolated CuII ion. As the temperature is lowered, the χ and
χT values increase smoothly to maxima at 5.9 and 10 K, respectively,
and then decrease rapidly. The data above 150 K follow the
The antiferromagnetic ordering is confirmed by the alternat-
ing-current thermal susceptibility measured under a zero direct-
current field (Figure S5 in the Supporting Information), which
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Inorganic Chemistry
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for two uncoupled S = 1/2 spins. As the temperature is lowered,
the product increases to a maximum of 1.05 emu molꢀ1 K at
29.7 K and then decreases rapidly, while the χ value increases
monotonically. The data above 100 K follow the CurieꢀWeiss
law with C = 0.88 cm3 K molꢀ1 and θ = 11.3 K. The high-
temperature behavior suggests an intradimeric ferromagnetic
coupling, while the low-temperature decrease in χT is attribu-
table to interdimeric antiferromagnetic interactions and/or zero-
field splitting (ZFS). FC and zero-field-cooled (ZFC) magneti-
zation measurements were performed over the temperature range
2ꢀ24 K under a low field of 10 Oe (Figure S7 in the Supporting
Information). The FC and ZFC data do not show divergence, and
the magnetization increases continuously with decreasing tempera-
ture; no maximum was observed. These observations indicate the
absence of any long-range magnetic ordering.
To evaluate the interactions, the magnetic behavior of the
dinuclear unit can be simulated with the modified Bleaneyꢀ
Bowers equation30 based on the Hamiltonian H = ꢀJS1 S2:
3
2Ng2β2
χdimer
¼
ð3Þ
kT½3 + expðꢀJ=kTÞꢁ
To get a better fit over the whole temperature range, the
molecular-field approximation (eq 2, replacing χchain with χdimer
)
was applied for the interdimeric interactions (zJ0) and the
temperature-independent paramagnetism was assumed to be
120 ꢂ 10ꢀ6 emu molꢀ1 per dimer. The best fit led to J =
93.6 cmꢀ1, g = 2.06, and zJ0 = ꢀ0.52 cmꢀ1. The positive J value
confirms a strong intradimeric ferromagnetic interaction through
the (COO)2(N3) triple bridge, while the negative zJ0 value
suggests interdimeric antiferromagnetic coupling.
Figure 6. (a) FC magnetization curves for 1 at different fields.
(b) Isothermal magnetization curves at 2 K for 1.
Alternatively, considering the ZFS within the S = 1 ground
state, which is conventionally assumed to be axial, the magnetic
susceptibility for the dimer can be expressed as1a
2x^ + x
χdimer
¼
ð4Þ
3
with χ = 2Ng2β2[exp(ꢀD/3kT)]/kT[exp(2D/3kT) + 2 exp-
(ꢀD/3kT) + exp(ꢀJ/kT) and χ^ = 2Ng2β2[exp(2D/3kT) ꢀ
exp(ꢀD/3kT)/D[exp(2D/3kT) +2exp(ꢀD/3kT) +exp(ꢀJ/kT)].
The fit of the experimental data to eq 4 with J, g, and D para-
meters failed to give satisfactory agreement. When both D and zJ0
are included by combining eqs 2 and 4, tꢀhe1 best fit gave J =
96.1 cmꢀ1, g = 2.06, and zJ0 = ꢀ0.52 cm with a negligible
D value (0.0004 cmꢀ1). The J, g, and zJ0 values are nearly the
same as those obtained using eqs 2 and 3. These results should
suggest that antiferromagnetic interactions are indeed operative
between dimers and are the main reason for the observed χT
decrease at low temperature.
We have described two new copper(II) compounds with
simultaneous azide and carboxylate bridges: 1 with (EO-N3)-
(COO) double bridges and 2 with (EO-N3)(COO)2 triple
bridges. To our knowledge, compound 2 is thus far the only
copper(II) species with (EO-N3)(COO)2 triple bridges, which
have been observed in several manganese(II) and cobalt(II)
compounds.18 Despite the remarkable differences in their brid-
ging multiplicity, coordination network, and bulk magnetic beha-
viors, both compounds show ferromagnetic coupling through
simultaneous bridges. As has been noted, one of the carboxylate
bridges in 2 adopts the basalꢀapical disposition between square-
pyramidal CuII ions. Because a CuII ion in the usual square-planar
(sp), square-pyramidal (spy), or axially elongated octahedral
Figure 7. Temperature dependence of χ and χT for 2 under 1 kOe. The
solid lines represent the best fit using eqs 2 and 3 (see the text).
exhibits a frequency-independent maximum in the real component
(χ0) at 6.2 K with zero imaginary signals (χ00). Metamagnetism is
confirmed by the sigmoidal shape of the isothermal magnetiza-
tion curve measured at 2 K, and the critical field is estimated to be
Hc = 6.1 kOe according to the dM/dH plot (Figure 6b). The slow
increase of magnetization at H < HC is consistent with antiferro-
magnetic ordering, while the rapid increase toward saturation at
high field is consistent with a ferromagnetic state. These features
indicate a spinꢀflip transition, for which the anisotropy field is
larger than the interchain exchange field.29 No evident hysteresis
was observed upon cycling of the field between ꢀ3 and 3 T at 2 K
(Figure S6 in the Supporting Information).
Complex 2. The susceptibility (χ) of complex 2 was measured
under 1 kOe in the 2ꢀ300 K range and is shown as χT and χ vs T
plots in Figure 7. The χT value per dimer at room temperature is
about 0.91 emu K molꢀ1, higher than the spin-only value expected
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Table 5. Structural and Magnetic Parameters for EquatorialꢀEquatorial (BasalꢀBasal) Carboxylate and EO-Azide Bridges in
Copper(II) Complexes
complexa
axialꢀaxial bridge
μ-Owater
CuꢀNꢀCu (deg)
Cu Cu (Å)
τb
J (cmꢀ1 c
)
ref
19d
3 3 3
[Cu1.5(N3)2(isonic)]n
106.7
103.2
116.2
106.5
107.6
119.5
111.9
106.6
124.3
126.8
108.2
116.9
105.5
113.6
107.0
109.4
101.1
3.20
3.12
3.39
3.19
3.22
3.44
3.28
3.22
3.52
3.54
3.23
3.41
3.19
3.35
3.18
3.25
3.08
0.11
0.22
0.29
Oct
0.11
Oct
Oct
Oct
0.22
Sp
80
[Cu1.5(hnta)(N3)2(H2O)]n
[Cu3(hnta)4(N3)2(H2O)3]n
[Cu(N3)(L1))(DMSO)]n
[Cu3(N3)4(L1)2(DMSO)2]n
[Cu2(N3)2(NO3)2(L2)2]n
{[Cu(Hpht)(N3)].H2O}n
89
35a
69.7
35a
μ-ODMSO
μ-ODMSO
μ-1,3-NO3
126
35b
126
26
35b
35c
75
35d
[Cu(INO)(N3)(H2O)0.5 n
]
μ-Ocarboxylate
80
35e
[Cu(NNO)(N3)(H2O)0.5 n
]
48
35e
[Cu(benzoate)(N3)]n
[Cu(L3)(N3)]n
33.9
16c
μ-1,1-N3
μ-OMeOH
Oct
Oct
Oct
0.54
0.13
0.01
0.11
0.48
93.1
65.6
63
16c
[Cu(1-naphthoate)(N3)]n
[Cu(N3)(tp)(CH3OH)]n
[Cu(N3)(nic)]n
16c
35f
39.1
68.8
63.9
96.1
19b
[Cu(N3)(p-CPA)]n
[Cu(4,3-pybz)(N3)]n
35g
this work
this work
[Cu2(4,4-pybz)3(N3)]n 3nH2O
μ-COO
3
a Isonic = isonicotinate, hnta = 6-hydroxynicotinate, L1 = μ1,3-(C4H3SCH2COO), L2 = Me3NCH2CO2, Hpht = hydrogen phthalate, INO =
isonicotinate N-oxide, NNO = nicotinate N-oxide, L3 = 2-methylbenzoate, tp = terephthalate; 4,3-pybz = 4-(3-pyridyl)benzoate; 4,4-pybz =
4-(4-pyridyl)benzoate, nic = nicotinate, p-CPAH = p-cyanophenoxyacetic acid. b The geometric parameter describes the distortion of square-pyramidal
coordination toward trigonal-bipyramidal. This is not applicable to octahedral and square-planar geometry. Oct = octahedral, Sp = square planar. c All of
the J values were quoted using the Hamiltonian H = ꢀ JS1 S2.
3
(oct) environment features a dx2ꢀy2-type magnetic orbital deloca-
lized toward basal (or equatorial) ligands from CuII with negligible
delocalization toward apical (or axial) ligands, the basalꢀapical
carboxylate bridge in 2 is a poor pathway for magnetic exchange
and may be neglected (it can be assumed that the additional
basalꢀapical bridge may influence magnetic exchange in an
indirect way, for instance, by altering the bridging parameters
of the basalꢀbasal bridges). Thus, the effective exchange path-
ways in 2 are similar to those in 1, including two dissimilar
basalꢀbasal bridges: a synꢀsyn carboxylate and an EO azide.
While the synꢀsyn carboxylate bridge in the basalꢀbasal (or
equatorialꢀequatorial, eqꢀeq) disposition always induces anti-
ferromagnetic exchange between CuII ions,10a the exchange
Figure 8. J and Cu Cu distances against the bridging CuꢀNꢀCu
3 3 3
through basalꢀbasal (or eqꢀeq) EO-azide bridges is sensitive
angle. The solid lines are just guides for the eye.
to the CuꢀNꢀCu angle, with a crossover from ferro- to anti-
ferromagnetic as the angle increases across 108ꢀ according to
empirical analyses31 or 104ꢀ according to a density functional
complexes are collected in Table 5. Note that some of these
theory study.32 However, the crossover angle is not valid for
compounds have a third bridge (μ1,3-NO3, μ-EO-N3, or μ-O) at
apical (or axial) positions around CuII ions, which has little
systems with simultaneous azide and carboxylate bridges, and the
contribution to magnetic exchange. The compounds with simul-
overall interaction is not the simple addition of contributions
taneous azide and carboxylate bridges but with one or both of the
from two individual bridges. Ferromagnetic coupling has been
bridges in axial positions34 are not included in the collection for
observed for mixed-bridged systems with large CuꢀNꢀCu
their evidently different magnetic properties.
angles, which are expected to induce antiferromagnetic coupling
in the absence of carboxylate. This has been justified by orbital
countercomplementarity:1a,33 the incorporation of the carbox-
ylate bridgereducestheenergygapbetweenthetwosinglyoccupied
molecular orbitals in the triplet state and hence diminishes (i.e.,
counterbalances) the antiferromagnetic contribution, leading to
overall ferromagnetic coupling (J = JF + JAF > 0 when |JAF| < JF).
To deduce general magnetostructural information for the
simultaneous basalꢀbasal (or eqꢀeq) azide and carboxylate
bridges, the structural and magnetic data for relevant copper(II)
As can be seen from Table 5, all of the copper(II) compounds
with simultaneous bridges exhibit ferromagnetic interactions,
independent of the CuꢀNꢀCu angle in the wide range of
101ꢀ127ꢀ. While no evident correlations can be deduced
between the J values and the structural parameters of the
carboxylate bridges, the magnitude of the interaction seems to
be mainly dependent upon the azide bridge. The J values are
plotted against the CuꢀNꢀCu angles in Figure 8. A general
trend is evident that the ferromagnetic interaction decreases as
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Inorganic Chemistry
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the bridging angle increases in the wide range from 101 to 127ꢀ.
The fluctuations may be due to unidentified structural factors
(for instance, the variations in the bridging mode of carboxylate)
or experimental uncertainty.
indicate antiferromagnetic coupling between MnII ions. The rise
in χ below 12 K may be due to the presence of a paramagnetic
impurity.
According to the structural data, the MnII ions in 3 are linked
into chains by EE-azide and OꢀH N bridges and are further
There is also a general trend that J decreases with the Cu
3 3 3
3 3 3
arranged in layers by two sets of double OꢀH O bridges.
Cu distance. This correlation is trivial because Cu Cu is
3 3 3
3 3 3
Although all of the bridges are triatomic with comparable Mn
mainly determined by the CuꢀNꢀCu angle (note that the
3 3 3
Mn separations, the magnetic interactions through the hydro-
gen-bonding pathways should be much weaker than those
through covalent bridges.36 Therefore, the system could be
treated as a quasi-1D system. A uniform antiferromagnetic chain
exhibits a characteristic susceptibility maximum at kTmax ≈ 0.5|J|
S(S + 1) (the Hamiltonian is H = ꢀJ∑SiSi+1),37a which indicates
the short-range antiferromagnetic order along the chain. From
CuꢀN distances for these compounds are very similar and vary
in the narrow range of 1.96ꢀ2.01 Å). The Cu Cu distances
3 3 3
are also plotted against the CuꢀNꢀCu angles in Figure 8 to
illustrate the linear increase of Cu Cu with CuꢀNꢀCu.
3 3 3
We note that compound 2 has the smallest CuꢀNꢀCu angle
and Cu Cu distance among all of these mixed bridging
3 3 3
systems, and the Cu2 coordination exhibits the largest distortion
from square-pyramidal to trigonal-bipyramidal. Because CuII in
this relationship, the intrachain exchange parameter of 3 (Tmax
=
25 K) could be estimated to be J = ꢀ4.0 cmꢀ1. To be more exact,
the well-known classical-spin equation derived by Fisher has
been used.37b
the trigonal-bipyramidal field has an axial magnetic orbital (dz2
)
and the azide bridge in this compound lies at an axial position, the
distortion does not prevent the azide bridge from being an
efficient pathway for magnetic exchange.
Ng2β2SðS + 1Þ 1 + u
Complex 3. The magnetic susceptibility of complex 3 was
measured inthe2ꢀ300 K temperature range under 1 kOe (Figure 9).
That measured at 300 K is about 3.83 emu K molꢀ1, which
indicates a high-spin MnII system with antiferromagnetic inter-
actions and rules out the possibility of a MnIII state (the spin-only
χchain
¼
ð5Þ
3kT
1 ꢀ u
where u is the Langevin function u = coth[JS(S + 1)/kT] ꢀ
kT/[JS(S + 1)]. The molecular-field approximation (eq 2) was
applied to include the possible interchain interactions through
hydrogen bonds, and a F parameter representing the molar
fraction of the paramagnetic impurity [assumed to be mononuclear
manganese(II) species, χimpurity = 4.375/T] has also been included
to account for the observed rise in χ below 10 K. With S = 5/2 and g
fixed at 2.00, the best fit in the whole temperature range led to J =
ꢀ4.16 cmꢀ1, zJ0 = 0.017, and F = 0.0098. The J value confirms the
antiferromagnetic interaction through a single EE-azide bridge,
while the very small zJ0 value indicates that the hydrogen bonds
transmit weak interactions between MnII ions.
values for high-spin MnII and MnIII are 4.38 and 3.00 emu K molꢀ1
,
respectively). Upon cooling, the χT value decreases monotoni-
cally, while the χ value increases to a broad maximum around
25 K and then increases rapidly upon further cooling below 10 K.
The data above 110 K follow the CurieꢀWeiss law with
C = 4.24 cm3 K molꢀ1 and θ = ꢀ32.4 K. The above features
Alternatively, the numerical approach
!
Ng2β2
A + Bx2
1 + Cx + Dx3
χchain
¼
ð6Þ
kT
proposed by Weng38a has been used to fit the data, where x =
|J|/2kT. The coefficients were determined by Hatfield et al. for
5
antiferromagnetic S = /2 chains: A = 2.9167, B = 208.04, C =
15.543, and D = 2707.2.38b The best fit of the experimental data
by combining eqs 2 and 6 and a F parameter generated an
unrealistically large zJ0 value. When this parameter is ignored, a
Figure 9. Temperature dependence of χ and χT for 3 under 1 kOe. The
solid lines represent the best fit to the Fisher model (see the text).
Table 6. Structural and Magnetic Parameters for the Single EE-Azide Bridges in 1D Manganese(II) Complexes
complexa
MnꢀN (Å)
MnꢀNꢀN (deg)
Mn Mn (Å)
MnꢀN3ꢀMn (deg)
J (cmꢀ1
)
ref
41a
3 3 3
{[Mn(N3)(dpyo)Cl(H2O)2](H2O)}n
2.21
2.22
2.29
2.21
2.24
2.15
2.18
2.21
2.23
127.6
159.8
122.0
140.0
136.7
144.1
142.8
146.0
124.0
6.13
6.63
6.01
6.40
6.35
5.93
5.97
6.03
5.34
180
180
127
180
165
26.1
86
ꢀ3.5
ꢀ0.12
ꢀ4.8
ꢀ4.4
ꢀ3.15
ꢀ4.7
ꢀ6.6
ꢀ5.3
ꢀ4.15
[Mn(L1)(N3)PF6]n
41b
[Mn(H2O)(μ-N3)(N3)(quinaz)2]n
[Mn2(3-ampy)4(μ-N3)2(N3)2(H2O)2]n
[Mn(R-L)2(N3)]n(ClO4)n
[Mn(L2)2(N3)]n(ClO4)n
[Mn(N3)2(L3)(CH3OH)]n
[Mn(4,40-pybz)(N3)(H2O)2]n
41c
41d
41e
41f
0.7
41g
74.5
this work
a dpyo = 4,40-dipyridyl-N,N0-dioxide, quinaz = quinazoline, 3-ampy = 3-aminopyridine, L1 = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo{12.3.1}-
octadeca-1,(18),2,12,14,16-pentaene, R-L = (R)-pyridine-2-carbaldehyde-imine, L2 = 4-methoxy-N-(pyridin-2-ylmethylene)aniline; L3 = (1E,2E)-1,
2-bis[phenyl(pyridin-4-yl)methylene)hydrazine, 4,4-pybz = 4-(4-pyridyl)benzoate.
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Scheme 1. Views Showing the Different Conformations of
the Single EE-Azide-Bridged MnꢀN3ꢀMn Moiety
graphics, χ0(T) and χ00(T) plots, isothermal magnetization, and
ZFC and FC magnetization curves. This material is available free
of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: eqgao@chem.ecnu.edu.cn. Fax: +86-21-62233404.
’ ACKNOWLEDGMENT
fairly good agreement has been obtained with J = ꢀ3.89 cmꢀ1
and F = 0.0111 with g = 2.00. The J and F values are in good
agreement with those obtained using eqs 2 and 5.
This work was supported by the NSFC (Grant 20771038) and
the Fundamental Research Funds for the Central Universities.
Several manganese(II) chains with single EE-azide bridges
have been reported in the literature, all exhibiting antiferromag-
netic interactions, as predicted for the bridge from extended
H€uckel molecular orbital calculations.39 Some relevant structural
and magnetic parameters are summarized in Table 6. The Mnꢀ
N3ꢀMn torsion angle (τ) varies widely from about 0 to 180ꢀ,
defining different conformations for the bridging moiety (Scheme 1):
the (quasi-)planar cis and trans conformations (τ ∼ 0 and 180ꢀ,
respectively) and the out-of-plane gauche conformation, with
τ deviating significantly toward 90ꢀ. The other structural para-
meters vary in the ranges 2.15ꢀ2.29 Å for MnꢀN, 122.0ꢀ159.8ꢀ
vary in the large range from ꢀ0.12 to ꢀ6.6 cmꢀ1. No unambiguous
magnetostructural correlations can be deduced from these data.
More systematic studies are needed for such multifactorial
systems, and besides the above-mentioned structural parameters,
other factors, for instance, the imprint of the diverse nonbridging
ligands upon magnetic orbitals, may also be important.40
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’ CONCLUSION
We have described three copper(II) and manganese(II) co-
ordination polymers with azide and two isomers of pyridylbenzoic
acid, 4,3-Hpybz, and 4,4-Hpybz ligands. Diverse structures and
magnetic properties have been observed. In compound 1, the CuII
ions are linked by mixed (μ-EO-N3)(μ-COO) double bridges to
give uniform chains, which are, in turn, linked into 2D layers by
the 4,3-pybz ligands. Compound 2 exhibits 2-fold interpenetra-
tion of 3D frameworks based on [Cu2(μ-EO-N3)(μ-COO)2]
units. Compound 3 contains 2D manganese(II) coordination
networks in which the chains with single μ-EE-N3 bridges are
interlinked by the 4,4-pybz ligands, and the structure also features
a 2D hydrogen-bonded network in which MnII ions are linked by
three kinds of double triatomic bridges, (μ-EE-N3)(OꢀH N),
3 3 3
(OwaterꢀH Owater)2, and (OwaterꢀH Ocarboxylate)2. The
3 3 3
3 3 3
magnetic properties of 3 are dominated by antiferromagnetic
interactions through the EE-azide bridges along the chain. The
simultaneous EO-azide and carboxylate bridges in 1 and 2 induce
ferromagnetic coupling between CuII ions. A magnetostructural
survey indicates a general trend that the ferromagnetic coupling
through the mixed bridges decreases as the CuꢀNꢀCu angle
increases. In addition, compound 1 exhibits antiferromagnetic
ordering below 6.2 K and behaves as a field-induced metamagnet.
’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic information
b
for compounds 1ꢀ3 in CIF format, supplementary structural
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