Solvothermal syntheses, structures, and physical properties of four new coordination compounds constructed from a bent dicarboxylate ligand

Article abstract of DOI:10.1039/c0dt00352b

Four new coordination compounds, namely {[Cd₃(L) ₂(μ₃-OH)₂(H₂O)]·H ₂O}_n (1), {Ni(L)(bipy)}_n (2), {Cu ₃(L)₂(bipy)(μ₂-OH)₂(DMF) ₂}_n (3), and {Co₂L₂(H ₂L)(H₂O)}_n (4), have been synthesized by the solvothermal reaction of 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) (H₂L) with different transition metal ions in the presence of co-ligand 4,4′-bipyridine (bipy). Compound 1 displays a three-dimensional (3D) framework containing infinite bands constructed of heptanuclear cadmium clusters. In compound 2, [Ni₂C₂O₄] secondary building units (SBUs) are linked by L^2- ligands into a 1D ribbon, which are further assembled into a two-dimensional (2D) non-interpenetrated structure with {4⁴·6²} topology. Compound 3 possesses a 3D framework with a new topology of {4³} ₂{4⁶·6¹⁴·8⁸} net, while the structure of 4 is a duplicate interpenetrated 3D framework with {4¹²·6³} net. Temperature-dependent magnetic studies reveal that 3 exhibits ferromagnetic coupling between adjacent Cu(ii) ions. The photoluminescent property of 1 has been studied in the solid state at room temperature.

Full text of DOI:10.1039/c0dt00352b

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www.rsc.org/dalton | Dalton Transactions
Solvothermal syntheses, structures, and physical properties of four new
coordination compounds constructed from a bent dicarboxylate ligand†
Changchun Ji,a Liangfang Huang,a Jing Li,a Hegen Zheng,*a,b Yizhi Lib and Zijian Guo*a
Received 21st April 2010, Accepted 12th June 2010
First published as an Advance Article on the web 3rd August 2010
DOI: 10.1039/c0dt00352b
Four new coordination compounds, namely {[Cd3(L)2(m3-OH)2(H2O)]·H2O}n (1), {Ni(L)(bipy)}n (2),
{Cu3(L)2(bipy)(m2-OH)2(DMF)2}n (3), and {Co2L2(H2L)(H2O)}n (4), have been synthesized by the
solvothermal reaction of 4,4¢-(hexafluoroisopropylidene)bis(benzoic acid) (H2L) with different
transition metal ions in the presence of co-ligand 4,4¢-bipyridine (bipy). Compound 1 displays a
three-dimensional (3D) framework containing infinite bands constructed of heptanuclear cadmium
clusters. In compound 2, [Ni2C2O4] secondary building units (SBUs) are linked by L2- ligands into a 1D
ribbon, which are further assembled into a two-dimensional (2D) non-interpenetrated structure with
{44·62} topology. Compound 3 possesses a 3D framework with a new topology of {43}2{46·614·88} net,
while the structure of 4 is a duplicate interpenetrated 3D framework with {412·63} net.
Temperature-dependent magnetic studies reveal that 3 exhibits ferromagnetic coupling between
adjacent Cu(II) ions. The photoluminescent property of 1 has been studied in the solid state at room
temperature.
With the aim of understanding the coordination chemistry of
Introduction
the H2L ligand and preparing new porous materials with not
Metal-organic frameworks (MOFs) are crystalline materials with
only interesting structures and topologies, but also good physical
high porosities and good thermal stability composed of metal
properties, especially the expected magnetic properties, we chose
ions or metal ion clusters.1 Some MOFs have been explored
H2L as the primary ligand and bipy as auxiliary co-ligand to react
for applications such as gas storage,2 catalysis,3 luminescence,4
magnetism5 and separations.6 Not only the aforementioned uses
but also the new structures and topologies of MOFs have attracted
more and more interest.7 The choice of metal ion and ligand
with the d-block metal ions, and successfully synthesized four com-
pounds {[Cd3(L)2(m3-OH)2(H2O)]·H2O}n (1), {Ni(L)(bipy)}n (2),
{Cu3(L)2(bipy)(m2-OH)2(DMF)2}n (3), and {Co2L2(H2L)(H2O)}n
(4). The details of their synthesis, structure, and physical properties
can be judiciously selected to influence the overall chemical
are reported below.
and physical properties of the MOFs. Accordingly, the most
effective and facile method to design two-dimensional (2D) and
three-dimensional (3D) metallosupramolecular species is to select
Experimental
appropriate organic ligands as building blocks with metal ions or
metal clusters as nodes.8
Materials and physical measurements
H2L and bipy ligands were purchased and used as received. All
other chemicals were of reagent grade quality from commercial
sources and were used without further purification. The IR
absorption spectra of the compounds were recorded in the range
of 400–4000 cm-1 by means of a Nicolet (Impact 410) spectrometer
with KBr pellets (5 mg of sample in 500 mg of KBr). C, H,
and N analyses were carried out with a Perkin-Elmer 240C
elemental analyzer. Luminescent spectra were recorded with a
SHIMAZU VF-320 X-ray fluorescence spectrophotometer at
room temperature (25 ◦C). Powder X-ray diffraction (PXRD)
measurements were performed on a Philips X’pert MPD Pro X-
ray diffractometer using Cu-Ka radiation (l = 0.15418 nm), in
which the X-ray tube was operated at 40 kV and 40 mA. The
as-synthesized samples were characterized by thermogravimetric
analysis (TGA) on a Perkin-Elmer thermogravimetric analyzer
Pyris 1 TGA up to 1023 K using a heating rate of 10 K min-1 under
a N2 atmosphere. Temperature dependent magnetic susceptibility
data for polycrystalline compound 3 was obtained on a SQUID
magnetometer under an applied field of 2000 Oe over the
temperature range of 1.8–300 K. The output data was corrected for
the experimentally determined diamagnetism of the sample holder
4,4¢-(hexafluoroisopropylidene)bis(benzoic acid) (H2L) as semi-
rigid dicarboxylate ligand has been investigated for its bent geom-
etry which can induce porous framework with many characters
such as selective adsorption, catalysis, magnetism, fluorescence
and so on.9 4,4¢-bipyridine (bipy) and the other linear N-donor
auxiliary co-ligands as bidentate pillar linkers have been used
widely for the construction of supramolecular architectures. The
research of compounds constructed by both H2L and bipy have
not been reported widely.10 It offered us an opportunity to find
more diversity of both structures and topologies in the field.
aState Key Laboratory of Coordination Chemistry, School of Chemistry and
Chemical Engineering, Nanjing National Laboratory of Microstructures,
Nanjing University, Nanjing, 210093, P. R. China. E-mail: zhenghg@
nju.edu.cn, zguo@nju.edu.cn; Fax: +86-25-83314502
bState Key Laboratory of Structural Chemistry, Fujian Institute of Research
on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002,
P. R. China
† Electronic supplementary information (ESI) available: Crystallographic
data, additional crystal figures, TGA, PL, PXRD for complexes. CCDC
reference numbers 767932, 767934–767936. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c0dt00352b
8240 | Dalton Trans., 2010, 39, 8240–8247
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and the diamagnetism of the sample calculated from Pascal’s
constants.
calculated for the product was lack and unsuccessfully repeated.
Anal. Calcd for C51H28F18O13Co2: C, 46.81%, H, 2.16%; found
C, 46.61%, H, 2.25%. IR(KBr, cm-1): 3414(s), 1697(s), 1637(s),
1616(s), 1576(m), 1560(m), 1539 (m),1 504(w), 1427(m), 1387(s),
1329(w), 1289(m), 1254(s), 1209(s), 1176(s), 1141(m), 1021(w),
971(w), 945(w), 930(w), 861(w), 844(w), 827(w), 783(m), 747(m),
724(m), 690(w), 623(w), 559(w), 491 (w), 473(w).
Synthesis of the compounds
Synthesis of {[Cd3(L)2(l3-OH)2(H2O)]·H2O}n (1). Cd(NO3)2·
4H2O (30.84 mg, 0.1 mmol) was added to an aqueous solution
of H2L (12 mg, 0.03 mmol), which was adjusted to pH ª 8.0
with NaOH. The final mixture was sealed in a 15 mL PTFE-lined
stainless-steel acid digestion bomb and heated at 170 ◦C for 96 h to
give colorless needle-like crystals of 1 with large quantities of white
powder. The pure crystals of 1 were isolated by filtration, washed
with distilled water and dried in air. Yield of the reaction was ca.
40% based on H2L. Anal. Calcd for C34H22O12F12Cd3: C, 34.38%,
H 1.87%; found C, 34.51%, H, 1.95%. IR(KBr,cm-1): 3447(s),
1597(m), 1547(m), 1412(m), 1291(w), 1254(m), 1212(m), 1175(m),
1141(w), 1022(w), 971(w), 944(w), 930(w), 858(w), 782(w), 749(w),
726(m), 690(w).
X-Ray crystallography
Single crystals of 1–4 were prepared by the methods described
in the synthetic procedure. X-ray crystallographic data of 1 was
collected at 123 K, and 2–4 were collected at room temperature
using epoxy-coated crystals mounted on glass fiber. All measure-
ments were made on a Bruker Apex Smart CCD diffractometer
˚
with graphite-monochromated Mo-Ka radiation (l = 0.71073 A).
The structures of 1–4 were solved by direct methods, and the
non-hydrogen atoms were located from the trial structure and
then refined anisotropically with SHELXTL using a full-matrix
least-squares procedures based on F2 values.11 The hydrogen atom
positions were fixed geometrically at calculated distances and
allowed to ride on the parent atoms. The relevant crystallographic
data are presented in Table 1, while the selected bond lengths and
angles are given in Table S1, ESI.†
Synthesis of {Ni(L)(bipy)}n (2). Ni(NO3)2·6H2O (29.08 mg,
0.1 mmol) was added to an aqueous solution of H2L (12 mg,
0.03 mmol) and bipy (5 mg, 0.03 mmol), which was adjusted
to pH ª 8.0 with NaOH. The final mixture was sealed in a
15 mL PTFE-lined stainless-steel acid digestion bomb and heated
at 180 ◦C for 45 h to give green rhombohedra crystals of 2
with large quantities of white powder. The pure crystals of 2
were isolated by filtration, washed with copious quantities of
ethanol and dried under ambient conditions. Yield of the reaction
was ca. 67% based on H2L. Anal. Calcd for C27H16F6O4N2Ni :
C, 53.59%, H, 2.67%, N, 4.63%; found C, 53.70%, H, 2.55%,
N, 4.56%. IR (KBr, cm-1): 3425(m), 1622(s), 1609(s), 1565(m),
538(m), 1488(w), 1428(s), 1414(s), 1401(s), 1319(w), 1292(m),
1244(s), 1216(s), 1178(s), 1140(m), 1068(w), 1046(w), 1023(w),
972(m), 932(m), 860(m), 843(w), 814(m), 782(m), 749(w), 726(m),
690(w), 635(m), 576(w), 544(w), 503(m).
Results and discussion
Synthesis
The compounds were synthesized by the reaction of M(NO3)2
=
=
(M Cd, Ni and Cu) or MCl2 (M Co) with H2L and bipy.
Solvothermal synthesis was applied to this system for multi-
dimensional coordination compounds. The formation of products
was not significantly affected by changes of the reaction mole
ratio of the ligands and metal salts. Many parallel experiments
proved that the quality of crystals depended on the pH, the solvent
and the temperature. Usually high temperature will increase the
dimensionality of connection and lead to polymeric compounds,
but it will lead to impure products at the same time. We selected
proper temperature and the other related factors by repeating
parallel experiments. Compounds 1, 2, and 4 were obtained at
high temperature above 160 ◦◦C for over 45 h, while 3 was obtained
at lower temperature of 90 C for only one day. In addition, the
aqueous solution of H2L in syntheses of compounds 1 and 2 were
adjusted to pH ª 8.0. The resultant crystals are stable in air and
insoluble in water or common organic solvents.
Synthesis of {Cu3(L)2(bipy)(l2-OH)2(DMF)2}n (3). A mix-
ture of H2L (12 mg, 0.03 mmol), bipy (5 mg, 0.03 mmol),
Cu(NO3)2·3H2O (24.16 mg, 0.1 mmol), and H2O–DMF (1 : 4,
v/v, 8 mL) was sealed in a 15 mL PTFE-lined stainless-steel acid
digestion bomb and heated at 90 ◦C for 24 h and then was cooled
to give large quantities of blue block crystals of 3 together with
some unrecognized absinthe-green polycrystalline materials. The
pure crystals of 3 were isolated by manual separation, washed
with DMF and water and dried in air. Yield of the reaction
was ca. 32% based on H2L. Anal. Calcd for C50H40F12O12N4Cu3:
C, 45.93%, H, 3.08%, N, 4.29%; found C, 45.41%, H, 3.38%,
N, 4.12%. IR(KBr, cm-1): 3415(m), 1671(s), 1610(s), 1558(m),
1549(m),1494(w), 1417(m),1387(s), 1324(w), 1291(m), 1252(s),
1240(m), 1224(m), 1207(m), 1172(s), 1143(m), 1133(m), 1096(m),
1078(m), 1047(w), 1019(w), 970(w), 942(w), 930(w), 859(w),
847(w), 827(w), 781(m), 748(m), 726(m), 687(w), 644(w), 542(w),
484(w), 458(m).
Crystal structures
Structure of {[Cd3(L)2(l3-OH)2(H2O)]·H2O}n (1). The archi-
tecture of compound 1 is a three-dimensional open framework.
Four crystallographically independent Cd(II) centers exist in an
asymmetric unit, in which Cd2 and Cd4 are half occupancy
but Cd1 and Cd3 are full occupancy. All the Cd(II) ions are
hexacoordinated. As illustrated in Fig. 1a, the Cd1 center presents
a slightly distorted octahedron, defined by six oxygen atoms
from four different L2- ligands, one m3-OH and one coordinated
water. The Cd–O bond distances vary in the range 2.223(4)–
Synthesis of {Co2L2(H2L)(H2O)}n (4). A mixture of H2L
(12 mg, 0.03 mmol), CoCl2·6H2O (23.79 mg, 0.1 mmol), and
H2O–DMF (8 mL/1 drop) was sealed in a 15 mL PTFE-lined
stainless-steel acid digestion bomb and heated at 160 ◦C for
48 h and then was cooled to give a little of purple needle-like
crystals of 4, which were isolated by filtration, and air-dried after
washed with DMF and water. Yield of the reaction could not be
˚
2.252(4) A. Cd2 adopts a octahedral coordination environment,
formed by four oxygen atoms from m3-OH which located at an
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Table 1 Crystallographic data and structure refinement details for compounds 1–4
Compound
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
C34H22O12F12Cd3
1187.72
Triclinic
¯
P1
7.5227(15)
14.626(2)
18.9971(18)
102.432(2)
94.761(3)
102.521(2)
1974.1(5)
2
1.998
1.717
1148
2.04, 26.00
10708, 7575
0.025
C27H16F6O4N2Ni
605.13
Triclinic
¯
P1
8.2819(14)
11.300(2)
14.848(3)
82.824(3)
74.649(4)
71.770(4)
1271.4(4)
2
1.581
0.845
612
1.90, 26.00
6904, 4879
0.0236
C50H40F12O12N4Cu3
1307.48
Monoclinic
C2/c
25.003(3)
8.107(2)
28.4059(19)
90.00
116.110(3)
90.00
5170.3(15)
4
1.680
1.333
2636
1.81, 26.00
13420, 5054
0.0362
C51H28F18O13Co2
1308.59
Monoclinic
P2/c
18.9503(19)
7.1992(7)
23.5351(17)
90.00
123.836(5)
90.00
2667.0(4)
2
1.630
0.748
1308
1.74, 26.00
13914, 5225
0.0494
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
Dc/g cm-3
m/mm-1
F(000)
q min-max/◦
Tot., uniq. data
R(int)
Observed data [I > 2s(I)]
Nref, Npar
5653
3452
3657
3619
7575, 538
0.0488, 0.1077
1.079
4879, 344
0.0593, 0.1190
1.009
5054, 368
0.0544, 0.0999
1.012
5225, 384
0.0636, 0.1339
1.002
R1, wR2 [I > 2s(I)]
GOF on F2
Min. and max resd
-1.14, 1.08
-0.31, 0.42
-0.52, 0.40
-0.39, 0.32
-3
˚
dens/e A
equatorial plane and two oxygen atoms from two L2- ligands
at the axial positions with the Cd–O distances ranging from
along b axis use mode-I to coordinate to metal atoms, the
other six ligands along c axis use both mode-II and III. Al-
though related examples of metal–organic polymers constructed
by cadmium clusters have been reported,14 but the band con-
structed by the heptanuclear cadmium clusters in compound 1 is
unprecedented.
˚
˚
2.273(4) A to 2.354(4) A. It is obvious that the angles of O4#9-
Cd2-O4#10, O9-Cd2-O9#11, O10-Cd2-O10#11 around the Cd2
center are all 180◦. In contrast, Cd3 exhibits distorted octahedral
geometry, which is coordinated by four oxygen atoms from three
different L2- ligands and two oxygen atoms from m3-OH, and the
˚
˚
distances of Cd–O ranges from 2.196(4) A to 2.474(4) A. Cd4
center displays an octahedral coordination environment similar
to Cd2. Differently, the equatorial plane is constructed by four
oxygen atoms belonging to four different L2- ligands and the axial
positions are occupied by two oxygen atoms from m3-OH with
Structure of {Ni(L)(bipy)}n (2). X-Ray diffraction reveals
that only one crystallographically independent Ni(II) center is
contained in the fundamental asymmetric unit (Fig. 2a). The
Ni(II) sites in “4+2” distorted octahedral geometry, defined by
two nitrogen donors from two separate bipy ligands occupying
the axial positions, and four oxygen atoms from three carboxylate
groups of the acid ligands in the equatorial plane. The atoms
in one ring of 4,4¢pyridine (C23–C27 and N2) were disordered
over two positions with occupancies of 0.48 and 0.52, respectively.
˚
˚
the Cd–O distances ranging from 2.156(4) A to 2.372(4) A. And
the angles of O1-Cd4-O1#2, O9-Cd4-O9#2, O3#6-Cd4-O3#10
are also 180◦. A heptanuclear cadmium cluster is formed by
seven cadmium atoms (two Cd1, two Cd2, two Cd3 and one Cd4
atoms) belonging to two asymmetric units through Cd–O bonds,
which looks like a flower containing six petals.12 The coordination
illustration of the cluster with twelve L2- ligands is shown in
Fig. 1a. Each heptanuclear cadmium cluster is connected to two
adjacent clusters by two Cd2 atoms resulting in infinite bands
constructed of cadmium clusters, which are further bridged by
the L2- ligands to complete the overall 3D network (Fig. 1b). The
deprotonated carboxylate groups of the L2- ligand adopt three
coordination modes respectively (Scheme 1).13 The six ligands
˚
The Ni–O distances are in the range 1.999(3)–2.121(3) A, and
˚
Ni–N distances vary in the range 2.079(3)–2.15(2) A, which
are comparable to those values found in other reported similar
complexes.15 As shown in Fig. 2b, the L2- ligand acts as a m3-bridge
through one m2-bridging carboxylate and two chelating oxygen
atoms to link three nickel (II) atoms. The second building unit
(SBU) is a dinickel carboxylate moiety ([Ni2C2O4]), where two Ni
atoms are bridged by two m2-bridging carboxylate groups of two
different L2- ligands, with Ni ◊ ◊ ◊ Ni distance of 4.5058(9) A. The
˚
[Ni2C2O4] SBUs are linked by two L2- ligands to result in a 1D
ribbon of [Ni2(L)2]n with the two adjacent dinickel cores distance
˚
of 11.6874(24) A. The two-dimensional (2D) double-layer network
structure of 2 is achieved by the bipy ligands coordinating to Ni
atoms in two adjacent 1D ribbons, whereas the Ni ◊ ◊ ◊ Ni distance
˚
with the bipy bridge is 11.3000(21) A (Fig. 2c). However, these
layers are tightly stacked one by one along the crystallographic a
axis (Fig. 2d). The structure of 2 can be simplified into a {44.62}
net.
Scheme 1 The coordination mode I, II and III.
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Fig. 1 a View of the metal coordination sphere in compound 1 with 30% ellipsoid probability (Right: the ligands are omitted for clarity). b View of 3D
framework of 1 containing the band of cadmium clusters along the a axis direction.
connected by bipy and L2- ligands in different directions to form
Structure of {Cu3(L)2(bipy)(l2-OH)2(DMF)2}n (3). As shown
the 3D porous framework as exhibited in Fig. 3b (right). With
the topological viewpoint, the Cu(II) centers can be viewed as 8-
connecting nodes, and all crystallographically independent L2-
ligands act as 3-connecting nodes, the whole structure can
be represented as a new {43}2{46.614.88} net, as displayed in
Fig. 3c.
in Fig. 3a, the asymmetric unit of 3 contains one and a half
Cu(II) ions, one m2-hydroxide, half a bipy ligand, and one L2-
ligand. The Cu1 ion sits on the bottom center in a distorted
square pyramidal geometry, it is coordinated by two oxygen atoms
from two L2- ligands, one oxygen atom from m2-OH and one
nitrogen atom from bipy ligand on the basal plane, and the last
one oxygen atom from another L2- ligand at the apical position.
The Cu–O distances in the square pyramid are in the range
Structure of {Co2(L)2(H2L)(H2O)}n (4). The structure of
˚
˚
from 1.888(2) to 2.351(3) A, and Cu–N distance is 2.053(3) A,
which are reasonably compared to those values of other reported
similar compounds.16 Cu2 is located in a square environment by
two oxygen atoms from two carboxylate groups and two oxygen
4 is isomorphous with that of the previously reported
[Cu(hfipbb)(H2hfipbb)0.5].18 The network of compound 4 is a
3D open framework containing only one crystallographically
independent Co(II) center in the fundamental asymmetric unit.
Each cobalt center has a square pyramidal coordination envi-
ronment formed by four oxygen atoms from four separate L2-
ligands occupying the equatorial plane, and one oxygen atom
from one carboxylate group of the protonated H2L ligand in
the axial positions. It is a different coordination mode compared
with those of compounds 1–3. Four carboxylate groups of the
four L2- ligands, two oxygen atoms of the H2L ligands, and two
Co atoms constructed a paddle-wheel with the Co–Co distance of
atoms from m2-OH with the Cu–O distances range from 1.810(2) to
17
˚
1.945(2) A, which are compared with those reported compounds.
Interestingly, the Cu2 atom is bridged to neighboring two Cu1
atoms by both the m2-OH and carboxyl groups from L2- ligands.
The adjacent “Cu1–Cu2–Cu1” units are linked by two carboxyl
groups to come into being a zigzag chain of Cu atoms, and the
˚
distances of Cu1–Cu2, Cu1–Cu1 are 3.3262(8) and 4.3599(9) A,
respectively (Fig. 3b, left). And the continuous zigzag chains are
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Fig. 2 a View of the coordination sphere in compound 2 with 30% ellipsoid probability (the H atoms are omitted for clarity). b > A 1D ribbon of
[Ni2(L)2]n along c axis in 2 (the H atoms and bipy ligands are omitted for clarity). c View of 2D crystalline framework of 2 (the H atoms are omitted for
clarity). d Schematic representations of interdigitation between layers in compound 2 (the H atoms and bipy ligands are omitted for clarity).
˚
Magnetic properties
2.9073(10) A as shown in Fig. 4a. Each paddle-wheel unit binds
to four adjacent paddle-wheel units through the four remaining
carboxylate groups of L2- to form an undulating 2D network.
A layered structure is formed by two such identical networks
consisting of micro channels, as shown in Fig. 4b. The adjacent
layers are further interconnected by monodentate carboxylate
groups of H2L ligands in the axial position to generate a 3D
duplicate interpenetrated network (Fig. 4c). A better insight into
the nature of 4 can be achieved by regarding paddle-wheel unit as
a six-connected node and the L2- ligand as a linear linker to reduce
multidimensional structures to simple node-and-linker nets. The
simplified structure of 4 is a duplicate interpenetrated {412.63} net
topology (Fig. 4d).
To investigate the magnetic properties of 3, the temperature
dependence of the magnetic susceptibility was investigated by
applying a magnetic field of 2000 Oe in the temperature range 1.8–
300 K. cM T and cM versus T data for 3 are shown in Fig. 5. The
cM T product of 3 at 300 K is 1.41 cm3 mol-1 K, slightly above the
value expected for three non-interacting S = 1/2 copper(II) ions
(1.36 cm3 mol-1 K for g = 2.2). This, along with the increase of cM T
upon cooling to a maximum of 1.91 cm3 mol-1 K at 14 K, indicates
the interplay of ferromagnetic interactions. Upon further cooling,
the cM T product drops abruptly to a value of 1.26 cm3 mol-1
at 1.8 K, suggesting the effect of antiferromagnetic interactions
K
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Fig. 3 a View of the coordination sphere in compound 3 with 30% ellipsoid probability (the H atoms are omitted for clarity). b View of 3D framework
of 3 (right) containing the zigzag chain (left) of Cu atoms along the b axis direction. (H atoms are omitted for clarity). c Topological illustration for the
3,8-connected network of 3. Blue nodes represent Cu atoms and yellow nodes represent L2- ligands.
and/or zero-field splitting at low temperatures. Since compound
3 has a trinuclear structure in which the Cu(II) ions are bridged by
both carboxylate oxygen atoms and m2-O atoms, the magnetic sus-
ceptibility data can be analyzed by the following expression based
on a Heisenberg Hamiltonian H = -2J(S1S2+S1S3) - 2J¢S2S3:19
results in parameters g = 2.16, J = 29.73 cm-1, and J¢ = 6.54 cm-1
with R = [(cMT)calcd-(cMT)obsd]2/(cMT)obsd = 2 ¥ 10-5.
2
Photoluminescent properties
The photoluminescent properties of the Compounds 1–4 were
studied in the solid state at room temperature, but only 1 is
observed to have a fluorescence at room temperature (Fig. S1,
ESI†). 1 showed a broad, weak violet photoluminescence around
425 nm upon excitation at 340 nm in the solid state, which suggest
that the fluorescence of 1 is caused by the ligand. There is no
obvious emission obtained for the free H2L ligand under the same
Ng2b2 1 + e2J −2J '/ kT +10e3J / kT
4kT
cM
=
×
1 + e2J −2J '/ kT + 2e3J / kT
Where J and J¢ are the coupling constants, N, g, b, and k have
their usual meanings. The best fit shown as the solid line in Fig. 7,
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Fig. 4 a View of the coordination sphere in compound 4 with 30% ellipsoid probability (H atoms and labels of C atoms in ph are omitted for clarity). b
The illustration of interpenetration in 4 by two 2D nets, identical in structure (shown in solid and translucent). c View of 3D crystalline framework of 4
(the duplicate interpenetrations are shown in green and red, respectively). d the AB packing mode of the 6-connected layers.
Conclusions
In this work, four new compounds have been successfully synthe-
sized under solvothermal conditions. The results proved that the
allianceofH2L and bipy ligands is good for diversity of the possible
compound structures. Magnetic studies indicate that compound
3 exhibits ferromagnetic coupling between adjacent Cu(II) ions.
The results reveal that the coordination mode of the H2L ligand
and the introduction of an auxiliary bipy ligand are important in
the formation of coordination frameworks and would enrich the
diversity of structures and topologies. Subsequent works will be
focused on the structures and properties of a series of coordination
compounds constructed by different linear assistant bipy ligands
and H2L ligand.
Fig. 5 Plot of cM T and cM vs T for 3. The solid line represent the best
simulations obtained with the models described in the text.
Acknowledgements
experimental conditions. Therefore, the visible light emission of
1 can be assigned to the decrease of non-radiative vibrational
transitions in the L unit, which arises from the coordination to
Cd(II) centers.20
This work was supported by grants from the Natural Science
Foundation of China (Nos. 20971065; 20721002) and National Ba-
sic Research Program of China (2010CB923303; 2007CB925103).
8246 | Dalton Trans., 2010, 39, 8240–8247
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