Hydrothermal synthesis, structures, and physical properties of four new flexible multicarboxylate ligands-based compounds

Article abstract of DOI:10.1021/ic801221r

Four new compounds of partially or wholly deprotonated 5,5′-(1,4- phenylenebis(methylene))bis(oxy)diisophthalic acid (H₄L1) and 5,5′-(1,3-phenylenebis(methylene))bis(oxy)diisophthalic acid (H ₄L2), namely {[Co(L1)_0.5]·(H₂O) ₂}_n (1), {[Mn(L1)0.5]·(H₂O) ₂}_n (2), ([Cu(H₂L1)](μ₂-bipy)} _n (bipy = 4, 4′-bipyridyl) (3), and {[Zn₂(L2)]. H₂O}_n (4) were synthesized in the presence or absence of auxiliary bipy ligand. Their structures have been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, IR spectra, and thermogravimetric analysis. Compounds 1 and 2 are isostructural and possess three-dimensional (3D) networks. In compound 3, multicarboxylate ligands and bipy ligands link Cu centers to generate a two-dimensional (2D) sheet structure which is further connected by intermolecular hydrogen bonds to form a 3D supramolecular structure. In compound 4, the Zn centers are connected by L2^4- anions to generate a 3D framework. Magnetic susceptibility measurements indicate that compounds 1 and 2 exhibit antiferromagnetic coupling between adjacent Co(II) ions and Mn(II) ions. The photoluminescent properties of the free H₄L1 and H₄L2 ligands and compound 4 have been studied in the solid state at room temperature. Both ligands and compound 4 exhibit strong violet emissions. Compared with the fluorescent emission of the ligand, the emission of 4 is red-shifted and enhanced.

Full text of DOI:10.1021/ic801221r

Inorg. Chem. 2008, 47, 9528-9536
Hydrothermal Synthesis, Structures, and Physical Properties of Four
New Flexible Multicarboxylate Ligands-Based Compounds
Zhaorui Pan,† Hegen Zheng,*,†,‡ Tianwei Wang,† You Song,† Yizhi Li,† Zijian Guo,†
and Stuart R. Batten*,§
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering,
Nanjing National Laboratory of Microstructures, Nanjing UniVersity, Nanjing 210093, P.R. China,
School of Chemistry, Monash UniVersity, Victoria, 3800, Australia, and State Key Laboratory of
Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of
Sciences, Fuzhou 350002, P.R. China
Received July 2, 2008
Four new compounds of partially or wholly deprotonated 5,5′-(1,4-phenylenebis(methylene))bis(oxy)diisophthalic
acid (H4L1) and 5,5′-(1,3-phenylenebis(methylene))bis(oxy)diisophthalic acid (H4L2), namely {[Co(L1)0.5]·(H2O)2}n
(1), {[Mn(L1)0.5]·(H2O)2}n (2), {[Cu(H2L1)](µ2-bipy)}n (bipy ) 4, 4′-bipyridyl) (3), and {[Zn2(L2)].H2O}n (4) were
synthesized in the presence or absence of auxiliary bipy ligand. Their structures have been determined by single-
crystal X-ray diffraction analysis and further characterized by elemental analysis, IR spectra, and thermogravimetric
analysis. Compounds 1 and 2 are isostructural and possess three-dimensional (3D) networks. In compound 3,
multicarboxylate ligands and bipy ligands link Cu centers to generate a two-dimensional (2D) sheet structure which
is further connected by intermolecular hydrogen bonds to form a 3D supramolecular structure. In compound 4, the
Zn centers are connected by L24- anions to generate a 3D framework. Magnetic susceptibility measurements
indicate that compounds 1 and 2 exhibit antiferromagnetic coupling between adjacent Co(II) ions and Mn(II) ions.
The photoluminescent properties of the free H4L1 and H4L2 ligands and compound 4 have been studied in the
solid state at room temperature. Both ligands and compound 4 exhibit strong violet emissions. Compared with the
fluorescent emission of the ligand, the emission of 4 is red-shifted and enhanced.
Introduction
as magnetism,5,6 photoluminescence,7,8 hydrogen stor-
age,9-11 and catalysis.12,13 An effective and facile method
for the design of two-dimensional (2D) and three-dimensional
(3D) metallosupramolecular species is still the appropriate
The rational design and synthesis of functional coordina-
tion architectures have recently been extensively explored
not only because of their intriguing variety of architectures1-4
but also because of their potential functional properties such
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* To whom correspondence should be addressed. E-mail: zhenghg@
nju.edu.cn (H.Z.), stuart.batten@sci.monash.edu.au (S.R.B.). Fax: 86-25-
83314502.
†
Nanjing University.
Fujian Institute of Research on the Structure of Matter, Chinese
‡
Academy of Sciences.
§
Monash University.
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9528 Inorganic Chemistry, Vol. 47, No. 20, 2008
10.1021/ic801221r CCC: $40.75  2008 American Chemical Society
Published on Web 09/24/2008

Flexible Multicarboxylate Ligands-Based Compounds
choice of well-designed organic ligands as bridges or terminal
groups (building blocks) with metal ions or metal clusters
as nodes.14 Among various organic ligands, multicarboxylate
ligands are often selected as multifunctional organic linkers
because of their abundant coordination modes to metal ions,
resulting from completely or partially deprotonated sites,
allowing for various structural topologies,15 and also because
of their ability to act as H-bond acceptors and donors to
assemble supramolecular structures.16 For example, aromatic
multicarboxylates (benzene dicarboxylate, benzene tricar-
boxylate, 4,4′-oxybis(benzoate), and ethylenedi(4-oxyben-
zoate)) have been investigated widely for the design and
synthesis of open framework complexes. However, the flex-
ible ligand 5,5′-(1,4-phenylenebis(methylene))bis(oxy)di-
isophthalic acid (H4L1) has not been explored up to now,
and only one compound [Cu24(L2)12(H2O)16(DMSO)8]n con-
structed from 5,5′-(1,3-phenylenebis(methylene))bis(oxy)di-
isophthalic acid (H4L2) was synthesized recently.17
Many topologies can be obtained by incorporating flexible
linker units into our bridging ligands to access diverse
architectures. Such linkers can be single-atom spacers, such
as methylene groups or ether oxygen atoms, or longer
spacers, such as three-atom propylene groups.18,19 In this
paper, we designed and synthesized two flexible and mul-
tidentate ligands H4L1 and H4L2, which have two benzene
dicarboxylate substituents attached to a central benzene ring
through two-atom flexible spacer groups. These two ligands
have four obvious characteristics: (1) Both ligands can
completely or partially deprotonated and adopt various
coordination modes when they coordinate to metals and thus
may produce various structural topologies, owing to their
tetradentate carboxylate arms and their flexible structures;
(2) They can act not only as a hydrogen bond acceptors but
also as a hydrogen bond donors, depending on the degree
of deprotonation; (3) The carboxylic groups can propagate
magnetic superexchange between metal centers; (4) They
have a large conjugated π-systems and therefore can combine
with d10 metals to construct useful photoluminescence
materials. With the aim of understanding the coordination
chemistry of these two versatile ligands and preparing new
porous materials with interesting structural topologies and
physical properties, we chose H4L1 and H4L2 as bridging
ligands to react with the d-block metal ions Co(II), Mn(II),
and Zn(II), and successfully synthesized compounds 1, 2,
and 4. In the presence of the auxiliary bipy ligand, H4L1
reacted with Cu(II) to give compound 3. The details of their
syntheses, structures, and physical properties are reported
below.
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Experimental Section
Materials and Methods. H4L1 and H4L2 ligands were prepared
according to the literature.20 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 spectro-
photometer at room temperature (25 °C). X-ray diffraction (XRD)
measurements were performed on a Philips X′pert MPD Pro X-ray
diffractometer using Cu KR radiation (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
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55, 519–522.
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Inorganic Chemistry, Vol. 47, No. 20, 2008 9529

Pan et al.
Table 1. Crystallographic Data and Structure Refinement Details for Compounds 1-4
compound
formula
formula weight
crystal system
space group
a (Å)
1
2
3
4
C12H11CoO7
326.14
monoclinic
C2/c
20.282(4)
15.220(3)
7.9736(17)
106.461(3)
2360.4(9)
8
C12H11MnO7
322.15
monoclinic
C2/c
20.607(4)
15.384(3)
8.1417(17)
107.167(3)
2466.0(9)
8
C34H24CuN2O10
684.09
monoclinic
C2/c
12.872(3)
11.015(2)
20.869(4)
102.120(4)
2892.9(10)
4
C24H16Zn2O11
611.11
monoclinic
C2/c
18.392(4)
16.462(4)
7.6238(17)
90.345(3)
2297.3(9)
4
b (Å)
c (Å)
ꢁ (deg)
V (Å3)
Z
Dc (g cm-3
)
1.836
1.485
1328
1.735
1.101
1312
1.571
0.823
1404
1.767
2.153
1232
µ(Mo Ka)(mm-1
F(000)
)
temperature(K)
293
293
291
291
theta min-max (deg)
tot., uniq. data
R(int)
2.09, 25.00
5728, 2065
0.0537
2.07, 25.00
6002, 2175
0.0511
2.00, 25.99
7617, 2845
0.0294
1.66, 25.99
6125, 2255,
0.0320
observed data [I > 2σ(I)]
1868
1784
2484
1805
Nref, Npar
2065, 181
0.0356, 0.1004
1.007
2175, 181
0.0500, 0.1074
1.003
2845, 218
0.0476, 0.1097
1.086
2255, 178
0.0694, 0.1081
1.057
R1, wR2 (all data)
S
min. and max resd dens (e ·Å-3
)
-0.406, 0.068
-0.547, 0.065
-0.240, 0.207
-0.531, 0.075
1023 K using a heating rate of 20 K min-1 under a N2 atmosphere.
Temperature dependent magnetic susceptibility data for polycrys-
talline compounds 1 and 2 were obtained on a SQUID magnetom-
eter under an applied field of 2000 Oe over the temperature range
of 2-300 K. Diamagnetic correction is considered as part of the
data analysis by the generalized molar susceptibility expression
(12 mg, 0.05 mmol), and H2O (7 mL) was sealed in a 15-mL PTFE-
lined stainless-steel acid digestion bomb and heated at 160 °C for
5 days and then was cooled to give little red block crystals of 3
and large quantities of gray powder. 3 was isolated by filtration,
washed with copious quantities of distilled water, and dried under
ambient conditions. Anal. Calcd for C34H24CuN2O10: C, 59.69%;
H, 3.54%; N, 4.09%. Found: C, 59.80%; H, 3.59%; N, 4.02%.
IR(KBr, cm-1): 3445(s), 1708(s), 1610(s), 1437(m), 1422(m),
1385(s), 1370(s), 1332(m), 1262(m), 1118(m), 1104(m), 1058(s),
824(m), 678(m), 498(w).
Synthesis of {[Zn2(L2)].H2O}n (4). A mixture of H4L2 (12 mg,
0.025 mmol), KOH (5 mg, 0.1 mmol), Zn(NO3)2·6H2O (12 mg,
0.05mmol), and H2O (7 mL) was sealed in a 15-mL PTFE-lined
stainless-steel acid digestion bomb and heated at 160 °C for 6 days
and then was cooled to give large quantities of white crystals of 4,
which were obtained by filtration and washed with water. The
sample was allowed to air-dry. Yield: 12.22 mg (80%) yield based
on metal. Anal. Calcd for C24H16O11Zn2: C, 47.17%; H, 2.64%.
Found: C, 47.26%; H, 2.72%. IR(KBr, cm-1): 3429(vs), 1628(m),
1555(s), 1525(s), 1458(s), 1385(vs), 1327(m), 1273(s), 1157(ws),
1135(m), 1070(m), 782(m),716(m), 578(ws).
X-ray Crystallography. Single crystals of 1-4 were prepared
by the methods described in the synthetic procedure. X-ray
crystallographic data of 1-4 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 KR radiation (λ ) 0.71073 Å).
The structures of compounds 1, 2, and 4 were solved by direct
methods, while compound 3 was solved by the heavy atom method,
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.22 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 Supporting Information, Table S1.
ꢀm ) ꢀCo + ꢀdia
(1)
where ꢀm is the observed molar susceptibility of compound 1, ꢀCo
is the temperature-dependent paramagnetic susceptibility of the
Co(II) ion, and ꢀdia is the diamagnetic correction according to the
data that have been tabulated21 as Pascal’s constants and constituent
corrections. Brunauer-Emmett-Teller (BET) surface areas and
pore-size distributions were measured using a Micromeritics
ASAP2000 adsorption analyzer.
Synthesis. Synthesis of {[Co(L1)0.5]·(H2O)2]}n (1). A mixture
of H4L1 (12 mg, 0.025 mmol), KOH (3 mg, 0.05 mmol),
CoCl2 ·6H2O (12 mg, 0.05 mmol), and H2O (7 mL) was sealed in
a 15-mL PTFE-lined stainless-steel acid digestion bomb and heated
at 160 °C for 5 days and then was cooled to give violet crystals of
compound 1 together with some unrecognized pink polycrystalline
material, which were isolated by filtration, and washed with water.
The sample was allowed to air-dry. Yield: 12.39 mg (76%) yield
based on metal. Anal. Calcd for C12H11CoO7: C, 44.19%; H, 3.40%.
Found: C, 44.30%; H, 3.28%. IR (KBr, cm-1): 3422(w), 3084(w),
1624(m), 1542(s), 1458(S), 1382(vs), 1324(m), 1264(m), 1244(m),
1132(w), 1040(m), 1024(w), 823(m), 779(m), 724(m), 466(w).
Synthesis of {[Mn(L1)0.5]·(H2O)2]}n (2). Similar to the prepara-
tion of 1, a hydrothermal reaction of H4L1 (12 mg, 0.025 mmol),
KOH (3 mg, 0.05 mmol), Mn(OAc)2 ·4H2O (12 mg, 0.05mmol),
and H2O (7 mL) was sealed in a 15-mL PTFE-lined stainless-steel
acid digestion bomb and heated at 160 °C for 5 days. The final
product contained large quantities of yellow crystals of 2, which
were filtered off, washed with copious quantities of distilled water,
and dried under ambient conditions. Yield: 11.60 mg (72%) yield
based on metal. Anal. Calcd for C12H11MnO7: C, 44.74%; H, 3.44%.
Found: C, 44.68%; H, 3.51%. IR (KBr, cm-1): 3449(s), 2975(W),
2363(W), 1627(s), 1542(s), 1458(S), 1382(s), 1322(m), 1262(m),
1242(m), 1131(w), 1039(m), 885(w), 821(m), 779(m), 722(m),
466(w).
(21) Boudrcaux, E. A.; Mulay, L. N. Theory and Applications of Molecular
Paramagnetism; Wiley-Interscience: New York, 1976; p 477 ff.
(22) Bruker 2000, SMART (Version 5.0), SAINT-plus (Version 6), SHELXTL
(Version 6.1), and SADABS (Version 2.03); Bruker AXS Inc.: Madison,
WI.
Synthesis of {[Cu(H2L1)](µ2-bipy)}n (3). A mixture of H4L1
(12 mg, 0.025 mmol), bipy (4 mg, 0.025 mmol), Cu(OAc)2 ·4H2O
9530 Inorganic Chemistry, Vol. 47, No. 20, 2008

Flexible Multicarboxylate Ligands-Based Compounds
Results and Discussion
connects with three L14- anions to form a 3D network. The
distortion of the aryloxy groups along each arm of the H4L1
ligand from the plane of the central benzene ring results in
a 3D channelled structure with three parallel tunnels along
the c axis: A, B, and C (Figure 1b). All the channels are
empty. In addition, the 3D structure is further stabilized by
hydrogen bonds between coordinated water molecules and
carboxylate O atoms (Supporting Information, Table S2).
A better insight into the nature of this intricate framework
can be achieved by the application of a topological approach,
reducing multidimensional structures to simple node and
connection nets. The Co(II) centers can be regarded as
3-connected nodes and all crystallographical independent
L14- ligands act as 6-connected nodes. Therefore, the whole
structure can thus be represented as a (42.8)2(44.62.88.10) net,
as displayed in Figure 1c.
Synthesis and IR Spectrum. Hydrothermal synthesis
under pressure and at low temperatures (100-200 °C) is a
straightforward and effective method for the preparation of
metal-organic coordination polymers.23 The hydrothermal
reaction of H4L1 with CoCl2 · 6H2O gave violet crystals of
compound 1 together with some unrecognized pink poly-
crystalline material. In the case of Mn2+, compound 2 appears
as a pure phase in 72% yield. Compound 3 appears as a
minor phase. Compound 4 appears as a pure phase in 80%
yield. It should also be pointed out that compounds 1, 2,
and 4 were highly reproducible for repeated synthesis under
the reaction conditions employed in this work. However,
compound 3 was difficult to reproduce and only characterized
by single X-ray crystallography, IR spectra, and elemental
analysis. The IR spectra of these compounds show the
characteristic bands of the L14-, [H2L1]2-, or L24- at
1630-1555 cm-1 for the asymmetric vibration and at
1454-1348 cm-1 for the symmetric vibration. The broad
bands at 3530-3400 cm-1 are assigned to the stretching
vibrations of COOH groups and H2O molecules. The absence
of absorption bands at 1720-1690 cm-1 in 1, 2, and 4
indicates the H4L1 or H4L2 ligand adopts the completely
deprotonated L14- or L24- form, whereas the presence of
strong peaks at 1708 cm-1 for 3 suggests the H4L1 ligand
adopts the partly deprotonated [H2L1]2- form, which is
consistent with the X-ray structural analysis. The Supporting
Information, Figure S1 shows the three coordination modes
of L14-, L24- and H2L12- observed in this work.
Crystal Structure of {[Cu(H2L1)](µ2-bipy)}n (3). The
asymmetric unit of 3 contains one Cu2+ cation, one bipy
ligand, and one H2L12- anion. As shown in Figure 2a, all
Cu atoms are six-coordinated by two nitrogen atoms from
2-
two bipy ligands and four oxygen atoms from two H2L1
anions, forming a slightly distorted octahedral geometry. The
distances of Cu1-O1, Cu1-O2, Cu1-N1, and Cu1-N2#2
are 1.9552(19) Å, 2.5606(20) Å, 1.991(3) Å, and 1.973(3)
Å, respectively. The angle of N2#2-Cu1-N1 is 180.0(1)°.
In compound 3, the H4L1 ligands only partially deprotonate.
Each deprotonated carboxylate group of H2L12- acts as a
bis-monodentate ligand (Supporting Information, Figure S1b)
to bridge two Cu(II) ions affording a uniform chain. These
chains are further cross-linked by bridging bipy ligands along
the c axis to generate a 2D rectangular grid layer with a
20.54 Å × 11.02 Å window (Figure 2b). The two protonated
carboxylate groups of the H2L12- motif contribute to the
stabilization of the structure through extensive hydrogen
bonds with the coordinated carboxylate oxygen atoms. The
adjacent layers are thus cross-linked into a 3D network
(Figure 2c, Supporting Information, Table S2).
Crystal Structures. Crystal Structures of 1 and 2.
Single-crystal X-ray diffraction analyses reveal that 1 and 2
are isostructural and crystallize in the monoclinic C2/c space
group, and thus only structure 1 will be discussed here. As
shown in Figure 1a, compound 1 consists of one kind of
Co(II) cation, which adopts a slightly distorted octahedral
geometry, coordinated by four carboxylate oxygen atoms
(O1#2, O2#2, O5, O7#3) from three different L14- anions
[Co-O:2.0200(18)-2.2643(17)Å;O-Co-O,60.11(6)-161.13(6)°],
and two water molecules (O3, O4) [Co1-O3: 2.1418(18)
Å; Co1-O4: 2.0740(17) Å; O4-Co1-O3: 87.52(7)°]. The
aryloxy groups along each arm of the H4L1 ligands are
indeed twisted at an angle of 50.21(2)° away from the plane
of the central benzene ring in compound 1. H4L1 ligand
adopts the completely deprotonated L14- form and acts as
an octadentate-chelating ligand. Four deprotonated carboxy-
late groups of the L14- anion adopt two kinds of coordination
modes (Supporting Information, Figure S1a). Two carboxy-
late groups of opposite sides of the aryloxy group adopt bis-
monodentate coordination modes to bridge two Co centers
with the Co · · · Co distance of 4.7849(9) Å, whereas another
two carboxylate groups coordinate to the same Co centers
by adopting chelating coordination modes.
Crystal Structure of {[Zn2(L2)].H2O}n (4). The Zn(II)
atom is coordinated by four oxygen atoms from four L24-
anions in a distorted tetrahedral arrangement, with the Zn-O
distance ranging from 1.929(3) Å to 1.960(3) Å. The aryloxy
groups along each arm of the H4L2 ligands are only slightly
twisted at an angle of 6.199(1)° away from the plane of the
central benzene ring in compound 4. The ligand, with a syn
conformation, adopts a completely deprotonated L24- form
and acts as an octadentate ligand. The deprotonated car-
boxylate groups of the L24- anion all adopt bis-monodentate
coordination modes to bridge two Zn centers. Each L24-
group thus coordinates to eight Zn(II) cations (Supporting
Information, Figure S1c) and each Zn(II) cation connects
with three L24- anions giving rise to a 3D structure
containing three parallel channels along the c axis: square-
shaped A, B, and nanoscaled channel C with dimensions of
10.24 Å × 14.75 Å (Figure 3b,c). Channels A and B are
empty, whereas channel C is occupied by guest water
molecules. In addition, the 3D structure is further stabilized
by hydrogen bonds between water molecules and carboxylate
Each L14- ligand coordinates to six Co(II) cations (Sup-
porting Information, Figure S1a) and each Co(II) cation
(23) (a) Lu, J. Y.; Runnels, K. R. Inorg. Chem. Commun. 2001, 4, 678–
681. (b) Lu, J. Y.; Schauss, V. Eur. J. Inorg. Chem. 2002, 1945–
1947. (c) Lu, J. Y.; Babb, A. M. Inorg. Chem. 2002, 41, 1339–1341.
Inorganic Chemistry, Vol. 47, No. 20, 2008 9531

Pan et al.
Figure 1. (a) Thermal Ellipsoid Plot (ORTEP) drawing of 1 showing 30% ellipsoid probability (hydrogen atoms are omitted for clarity). Symmetry codes:
#1 ) x, -y, 0.5 + z; #2 ) 0.5 - x, 0.5 - y, - z; #3 ) x, -y, -0.5 + z. (b) A view of three kinds of channels of compound 1 along the c axis (hydrogen
atoms are omitted for clarity). (c) Schematic representation of the topology of compound 1. Blue nodes represent Co atoms and green nodes represent L14-
ligands.
O atoms (Supporting Information, Table S2). From a
topological viewpoint, the Zn(II) centers can be viewed as
4-connecting nodes, and all crystallographically independent
L24- ligands act as 8-connecting nodes. Therefore, the whole
structure can thus be represented as a (46)2(412.612.84) net,
as displayed in Figure 3d. The total void value of the
9532 Inorganic Chemistry, Vol. 47, No. 20, 2008

Flexible Multicarboxylate Ligands-Based Compounds
Figure 2. (a) ORTEP drawing of 3 showing 30% ellipsoid probabilities (hydrogen atoms are omitted for clarity). Symmetry codes: #1 ) x, -1 + y, z; #2
) x; 1 + y, z; #3 ) 1 - x, y, 0.5 - z. (b) A 2D sheet formed in compound 3. (Color code:white, C; red, O; blue, N; green, H; turquiose, Cu). (c) View of
the 3D supramolecular network constructed from 2D sheets by hydrogen bonds in 3. Pink dotted lines represent hydrogen bonds and turquoise solid bonds
represent bipy ligands (hydrogen atoms of phenyl rings are omitted for clarity; color code: white, C; red, O; green, H; turquoise, Cu).
Inorganic Chemistry, Vol. 47, No. 20, 2008 9533

Pan et al.
Figure 3. (a) ORTEP drawing of 4 showing 30% ellipsoid probabilities (hydrogen atoms and solvent molecules are omitted for clarity). Symmetry codes:
#1 ) x, -y, -0.5 + z; #2 ) 0.5 - x; -0.5 + y, 2.5 - z; #3 ) x, -y, 0.5 + z; #4 ) 0.5 - x, 0.5 - y, 3 - z; #5 ) 0.5 - x, 0.5 + y, 2.5 - z. (b) A view
of three kinds of channels of compound 4 along the c axis (hydrogen atoms are omitted for clarity). (c) Space-filling diagram showing the packing arrangement
of compound 4 along the c axis (solvent molecules are omitted for clarity). (d) Schematic representation of the topology of compound 4. Blue nodes
represent Co atoms and green nodes represent L24- ligands.
channels without water guests is estimated (by Platon24) to
be 308.7 Å3, approximately 13.4% of the total crystal volume
of 2297.3(3) Å3. All the solvent water molecules are
accommodated in a disordered fashion in the channels C.
To evaluate the permanent porosity of the framework of
compound 4, nitrogen sorption isotherm measurements
(Supporting Information, Figure S2) were performed on a
desolvated crystalline sample at 77 K. It shows a typical type-
III gas sorption behavior and an N2 uptake of approximately
20.45 cm3 (STP)/g, with a Langmuir surface area of 9.4699
m2/g and BET surface area of 6.7893 m2/g.
Magnetic Properties of 1 and 2. The temperature
dependence of the magnetic susceptibility of 1 in the form
Figure 4. Temperature dependence of magnetic susceptibility in the form
of ꢀMT and ꢀM versus T for 1. The solid lines are the fits of the data.
of ꢀMT and ꢀM versus T are displayed in Figure 4. At room
temperature, ꢀmT is equal to 6.12 cm3 · K · mol-1, which is
prominent orbital contribution. Upon lowering the temper-
much higher than the spin-only value of 3.75 cm3 · K · mol-1
based on two Co(II) ions (g ) 2 and s ) 3/2) because of the
ature, ꢀmT continuously decreases and reaches 2.36
cm3 ·K·mol-1 at 1.8 K. Above 120 K (Supporting Informa-
tion, Figure S3), the magnetic properties of 1 obey the
Curie-Weiss law and give C ) 6.50(2) and θ ) -18.2(6)
(24) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7–13.
9534 Inorganic Chemistry, Vol. 47, No. 20, 2008

Flexible Multicarboxylate Ligands-Based Compounds
mean-field corrections zj′ were taken into account, the
magnetic susceptibility in the whole temperature range was
fitted to eqs 3 and 4, which are deduced from the spin
ˆ
b b
Hamiltonian H ) -2JS1 · S2,
ꢀ )
2Ng2ꢁ2
e
2J⁄kT + 5e6J⁄kT + 14e12J⁄kT + 30e20J⁄kT + 55e30J⁄kT
×
1 + 3e2J⁄kT + 5e6J⁄kT + 7e12J⁄kT + 9e20J⁄kT + 11e30J⁄kT
kT
(3)
ꢀ
ꢀM )
(4)
1 - (2zj ’ ⁄ Ng2ꢁ2)ꢀ
where all symbols have their normal meanings. The best
fitting gave J ) -1.94(4) cm-1 and zj′ ) -0.48(1) cm-1
with a reasonable g-factor (1.96(1)), and the J value is
comparable with those in carboxylate bridging Mn(II)
compounds reported previously.29 These results indicate that
there exists weakly antiferromagentic interactions within the
Mn2 unit.
Figure 5. Temperature dependence of the magnetic susceptibility in the
form of ꢀMT and ꢀM versus T for 2. The solid lines are the fits of the data.
K. The obtained Weiss constant of close to -20 K for
noninteracting Co2+ ions25 indicates single-ion behavior of
Co(II) ion above 120 K in 1. According to the preceding
structure description of 1, no appropriate model could be
used for fitting the magnetic properties of such a system.
So, the treatment method reported by Rueff et al.26 and the
simple phenomenological eq 227 can be used here:
Luminescent Property. Luminescent compounds are
currently of great interest because of their various applica-
tions in chemical sensors, photochemistry, and electrolumi-
nescent displays.30 Previous studies have shown that coor-
dination polymers containing zinc and cadmium ions exhibit
photoluminescent properties.31 The photoluminescent proper-
ties of free ligands and compound 4 have been investigated
in the solid state at room temperature. Both ligands and
compound 4 display strong violet luminescence (Figure 6,
Supporting Information, Figure S4). Upon excitation at 350
nm, 4 exhibits strong fluorescent emission bands at 426 nm.
The peaks of 426 nm for the compound 4 exhibit a red-shift
(about 15 nm) with respect to the free H4L2 ligand (411 nm,
Figure 6). It is probably due to the decreased energy between
the highest occupied molecular orbital (HOMO) and the
lowest unoccupied molecular orbital (LUMO) of deproto-
nated L24- anions by coordinating to metal centers. The high-
dimensional structure of compound 4 leads to significant
enhancement of fluorescence intensity compared to that of
ꢀmT ) A exp(-E /kT) + B exp(-E /kT)
(2)
1
2
where A + B equals the Curie constant, and E1 and E2
represent the “activation energies” corresponding to the
spin-orbit coupling and to the magnetic exchange interac-
tion, respectively. The best fitting results give -E1/k )
-52.4(1) K and -E2/k ) -0.8(9) K with C ) 6.62 cm3 K
mol-1. Thus, the magnetic coupling constants between Co(II)
ions are -1.78 K for 1 according to the relationship of ꢀmT
∝ exp(+J/2kT).28 This indicates that the weak antiferromag-
netic exchange interaction between Co(II) ions with
spin-orbital coupling of Co(II) ions dominate the magnetic
properties in 1.
The temperature dependence of the magnetic susceptibility
of 2 in the form of ꢀMT and ꢀM versus T is displayed in Figure
5. As the temperature cools, ꢀMT continuously decreases from
8.23 cm3 · K · mol-1 at 300 K to 1.03 cm3 · K · mol-1 at 1.8 K,
indicating antiferromagnetic coupling between Mn ions.
From the viewpoint of crystal structure, it could be presumed
that the main magnetic interactions between the metal centers
might happen between two carboxylate bridged Mn(II) ions,
whereas the superchange interactions between Mn(II) ions
through the L14- ligands can be ignored because of the long
length of the L14- ligands. The magnetic susceptibility data
were fitted assuming that the carboxylate bridges of the
Mn(II) ions form an isolated spin dimer system. When the
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Inorganic Chemistry, Vol. 47, No. 20, 2008 9535

Pan et al.
tried the measurement again upon the crystal samples, but
we got the same outcome. It is thus likely that the samples
adsorbed guest molecules slowly from the air at room
temperature,33 and the decomposition of the anhydrous
composition occurs at 450 °C. To confirm whether the crystal
structures are truly representative of the bulk materials, XRD
experiments were carried out for 1, 2, and 4. The XRD
experimental and computer-simulated patterns of the corre-
sponding compounds are shown in the Supporting Informa-
tion, Figures S6-S8, and they show that the bulk synthesized
materials and the measured single crystals are the same.
Conclusion
This contribution has described the synthesis and properties
of four new compounds built from the H4L1 and H4L2
ligands. The results reported here will enrich the field of
metal-organic frameworks based on long flexible multicar-
boxylate ligands. Magnetic studies reveal that both compound
1 and 2 exhibit antiferromagnetic coupling between adjacent
Co(II) ions and Mn(II) ions. Compound 4 exhibits strong
violet emissions and may be a good candidate for violet-
light emitting materials.
Figure 6. Solid-state photoluminescent spectra of 4 and free ligand (H4L2)
at room temperature.
the free ligand. The enhanced luminescence efficiency can
be attributed to L24- anions coordinated to Zn(II) ions
resulting in a decrease in the nonradiative decay of intraligand
excited states.32
Thermal Analysis and XRD Results. To characterize the
compounds more fully in terms of thermal stability, their
thermal behaviors were studied by TGA (Supporting Infor-
mation, Figure S5). For compound 1, a rapid weight loss is
observed from 30 to 157 °C which is attributed to the loss
of the coordinated water molecules, with a weight loss of
11.28% (calcd 11.04%). The TGA curve of 2 shows that 2
undergoes dehydration between 20 and 170 °C, which is
again attributed to loss of the coordinated water molecules,
with a weight loss of 10.71% (calcd 11.04%). The decom-
position of the anhydrous residue of 1 and 2 occurs at 380
°C. In the case of 4, a rapid weight loss is observed from 25
to 170 °C, which is attributed to the release of the lattice
water with a weight loss of 4.82% (calcd 2.94%) between
20 and 170 °C. This result was unexpected, and thus we
Acknowledgment. This work was supported by grants
from the Natural Science Foundation of China (Nos.
20571039; 20721002), National Basic Research Program of
China (2007CB925103), and the Nature Science Foundation
of Jiangsu province (No. BK2006124).
Supporting Information Available: Crystallographic data in
CIF format, selected bond distances and angles, hydrogen bonding
geometry, additional figures, TGA plots of compounds 1, 2, and 4,
and XRD patterns of compounds 1, 2, and 4. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC801221R
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Growth Des. 2008, 8, 665–670.
(33) Li, S. L.; Lan, Y. Q.; Ma, J. F.; Yang, J.; Wei, G. H.; Zhang, L. P.;
Su, Z. M. Cryst. Growth Des. 2008, 8, 675–684.
9536 Inorganic Chemistry, Vol. 47, No. 20, 2008