Syntheses, characterizations and properties of five new metal-organic complexes based on flexible ligand 4,4′-(phenylazanediyl)dibenzoic acid

Article abstract of DOI:10.1039/c2ce26521d

Five new metal-organic frameworks have been synthesized under hydrothermal conditions, in CH₃CN-H₂O, DMF-CH₃CH ₂OH-H₂O and DMA-H₂O, namely, [ZnL(bimx) _0.5]_n (1), {[CoL(4,4′-bipy)]·DMF}_n (2), {[CdL(4,4′-bipy)]·DMF}_n (3), {[ZnL(bibp)] ·DMA·(H₂O)₂}_n (4), {[CoL(bpyb)_0.5]·(H₂O)₂}_n (5) (bimx = 1,4-bis(imidazol-1-ylmethyl)benzene, 4,4′-biby = 4,4-pyridine, bibp = 4,4′-bis(imidazol-1-yl)biphenyl, bpyb = 1,4-bis(4-pyridyl)benzene, H₂L = 4,4′-(phenylazanediyl)dibenzoic acid. These complexes were characterized by elemental analysis, IR spectroscopy, TG and X-ray single-crystal diffraction. In compounds 1, 2 and 3, the bimx, 4,4′-bipy and L^2- anions act as bidentate ligands assembling with metal cations to form two-dimensional (2D) sheets. The sheets are stacked in ABAB fashion and accumulate into a 3D framework. Compound 4 possesses a 3D→3D 4-fold interpenetrating architecture with {6⁵·8} topological net, which is similar to the cds topology. Compound 5 also displays a 3D structure with {4⁴·6¹⁰·8} topology. The photochemical properties were investigated in the solid state at room temperature. The luminescent properties of compounds 1, 3 and 4 are discussed in detail. The UV-vis absorption spectra of compounds 2 and 5 are tested and discussed. In addition, the magnetic properties of compound 5 also are tested and simply analyzed.

Full text of DOI:10.1039/c2ce26521d

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PAPER
Syntheses, characterizations and properties of five new
metal–organic complexes based on flexible ligand 4,49-
(phenylazanediyl)dibenzoic acid3
Cite this: CrystEngComm, 2013, 15,
616
Jianliang Zhou,*a Yuanyuan Wang,a Ling Qin,b Mingdao Zhang,b Qingxiang Yangb
and Hegen Zheng*b
Five new metal–organic frameworks have been synthesized under hydrothermal conditions, in CH3CN–
H2O, DMF–CH3CH2OH–H2O and DMA–H2O, namely, [ZnL(bimx)0.5 n
]
(1), {[CoL(4,49-bipy)]?DMF}n (2),
1,4-
{[CdL(4,49-bipy)]?DMF}n (3), {[ZnL(bibp)]?DMA?(H2O)2}n (4), {[CoL(bpyb)0.5]?(H2O)2}n (5) (bimx
=
bis(imidazol-1-ylmethyl)benzene, 4,49-biby = 4,4-pyridine, bibp = 4,49-bis(imidazol-1-yl)biphenyl, bpyb =
1,4-bis(4-pyridyl)benzene, H2L = 4,49-(phenylazanediyl)dibenzoic acid. These complexes were characterized
by elemental analysis, IR spectroscopy, TG and X-ray single-crystal diffraction. In compounds 1, 2 and 3, the
bimx, 4,49-bipy and L22 anions act as bidentate ligands assembling with metal cations to form two-
dimensional (2D) sheets. The sheets are stacked in ABAB fashion and accumulate into a 3D framework.
Compound 4 possesses a 3DA3D 4-fold interpenetrating architecture with {65?8} topological net, which is
similar to the cds topology. Compound 5 also displays a 3D structure with {44?610?8} topology. The
photochemical properties were investigated in the solid state at room temperature. The luminescent
properties of compounds 1, 3 and 4 are discussed in detail. The UV-vis absorption spectra of compounds 2
and 5 are tested and discussed. In addition, the magnetic properties of compound 5 also are tested and
simply analyzed.
Received 18th September 2012,
Accepted 31st October 2012
DOI: 10.1039/c2ce26521d
www.rsc.org/crystengcomm
geometries of the organic ligands have a great effect on the
structural frameworks of coordination polymers; thus, much
Introduction
In the fields of supramolecular chemistry and crystal
engineering, the design and assembly of metal–organic
coordination polymers become more and more popular
because of an intriguing variety of architectures, topologies
and potential applications in gas storage, ion-exchange,
heterogeneous catalysis, magnetism, non-linear optics, mole-
cular sensing, and electrical conductivity.1–4 In recent years,
researchers focus on designing and assembling the targeted
structures of coordination polymers. In this respect, the
rational and controllable preparation of metal–organic frame-
works (MOFs) is one of the obvious challenges. MOFs are
greatly affected by factors such as the organic ligands,5 the
nature of metal ions,6 temperature,7 solvent,8 counterions,9
and so on. In order to build novel molecular architectures, the
effort has been devoted to modifying the building blocks and
to controlling the assembled motifs for required products via
selecting different organic ligands.10,11 The reported research
works show that multiple carboxylate ligands have been used
as ideal organic linkers for building MOFs.12 This is because
their different coordination modes lead to diverse multi-
dimensional architectures. As far as we know, elongated
dicarboxylate ligands, tricarboxylate ligands and tetracarbox-
ylate ligands have been employed by several groups to
construct porous MOFs.13–15 Recently, non-rigid ligands have
usually been the typical building elements in the multi-
dimensional networks. The flexible ligands have variable
coordination modes, and can adopt a variety of conformations
according to the restrictions imposed by the coordination
geometry of the metal ion, to meet the coordination require-
ments of the metal ions,16a which can result in more
topological structures than a rigid ligand.16b Therefore, we
design and synthesize a ‘‘V-shaped’’ flexible ligand of 4,49-
(phenylazanediyl)dibenzoic acid. Auxiliary ligands are also a
good choice for the construction of novel polymeric structures.
aSchool of Chemistry and Chemical Engineering, Central South University,
Changsha, 410083, China. E-mail: zhoujl@csu.edu.cn; Fax: +86-731-88879616
bState 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;
Fax: +86-25-83314502
Electronic supplementary information (ESI) available: Crystallographic data in
3
A
large number of metal–organic frameworks that are
CIF format, selected bond lengths and angles, and patterns of photochemistry,
TGA and PXRD. CCDC 900963–900967. For ESI and crystallographic data in CIF
format or other electronic format see DOI: 10.1039/c2ce26521d
assembled by mixed-ligands and metal ions have been
reported, showing that the combination of different ligands
616 | CrystEngComm, 2013, 15, 616–627
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under N2 atmosphere. Temperature dependent magnetic
susceptibility data for polycrystalline complex 5 were obtained
on a SQUID magnetometer under an applied field of 2000 Oe
over the temperature range of 1.8–300 K.
can result in greater tenability of structural frameworks than
single ligands.17,18 The ligands containing imidazole or
pyridine are regarded as important auxiliary ligands in the
design and assembly of metal–organic coordination polymers.
Hence, to obtain novel MOFs, we select 1,4-bis(imidazol-1-
ylmethyl)benzene (bimx) 4,49-bipyridine (4,49-bipy), 4,49-bis(i-
midazol-1-yl)biphenyl (bibp) and 1,4-bis(4-pyridyl)benzene
(bpyb) as the auxiliary ligands (Scheme 1). In the present
work, we have synthesized five new coordination compounds
SYNTHESIS OF [ZNL(BIMX)0.5
] (1). A mixture of Zn(NO3)2?6H2O
n
(29.7 mg, 0.1 mmol), H2L (33.3 mg, 0.1 mmol) and bimx (23.8
mg, 0.1 mmol) was dissolved in mixed solvents (4 mL of
distilled H2O and 4 mL of CH3CN). The final mixture was
placed in a Parr Teflon-lined stainless steel vessel (15 mL)
under autogenous pressure and heated at 130 uC for three
days. Large quantities of colorless-block crystals were obtained
and the crystals were filtered off, washed with distilled water,
and dried under ambient conditions. Yield of the reaction was
ca. 63% based on the H2L ligand. Anal. calcd for
with intriguing structures, namely, [ZnL(bimx)0.5 n
]
(1),
{[CoL(4,49-bipy)]?DMF}n (2), {[CdL(4,49-bipy)]?DMF}n (3),
{[ZnL(bibp)]?DMA?(H2O)2}n (4), {[CoL(bpyb)0.5]?(H2O)2}n (5).
All the compounds were characterized by elemental analysis,
IR spectrum, X-ray crystallography and powder X-ray diffrac-
tion (PXRD). The details of their syntheses, structures and
properties are reported below.
C
27H20N3O4Zn: C, 62.86%, H, 3.91%, N, 8.15%; found: C,
62.55%, H, 3.96%, N, 8.34%. IR (KBr, cm21): 3454(w), 3130(w),
1592(s), 1548(m), 1526(m), 1491(s), 1406(s), 1370(s), 1309(m),
1267(s), 865(w), 785(w), 706(w), 695(w), 658(w), 558(w), 564(w).
SYNTHESIS OF {[COL(4,49-BIPY)]?DMF}n (2). Co(NO3)2?6H2O (29.1
mg, 0.1 mmol), H2L (33.3 mg, 0.1 mmol) and 4,49-bipy (15.6
mg, 0.1 mmol) were added to a mixed solvent of 2 mL of
distilled H2O, 2 mL of C2H5OH and 2 mL of DMF. The final
mixture was sealed in a 15 mL Parr Teflon-lined stainless-steel
under autogenous pressure and heated at 80 uC for three days.
Large quantities of rose red-block crystals were obtained and
the crystals were filtered off, washed with quantities of
distilled water, and dried under ambient conditions. Yield of
the reaction was ca. 65% based on the H2L ligand. Anal. calcd
for C33H28CoN4O5: C, 63.98%, H, 4.56%, N, 9.04%; found: C,
64.05%, H, 4.61%, N, 9.25%. IR (KBr, cm21): 3426(m), 2363(w),
1633(m), 1595(s), 1547(m), 1489(w), 1414(s), 1329(m), 1277(m),
1220(m), 1180(m), 1068(w), 851(w), 812(w), 781(w), 754 (w),
702(w), 630 (w), 573 (w), 532(w).
Experimental
Materials and methods
The H2L was synthesized by 4-fluorobenzonitrile and pheny-
lamine then hydrolyzing.19 Bibp, bimx and bpyb ligands were
prepared by the literature methods. Reagents and solvents
employed were commercially available and used as received.
IR absorption spectra of the complexes were recorded in the
range of 400–4000 cm21 on a Nicolet (Impact 410) spectro-
meter 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. Powder X-ray diffraction (PXRD) measure-
ments were performed on
a Bruker D8 Advance X-ray
diffractometer using Cu Ka radiation (1.5418 Å), 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 750 K using a heating rate of 10 K min21
SYNTHESIS OF {[CDL(4,49-BIPY)]?DMF}n (3). Complex 3 was
prepared in the same way as for 2 by using Cd(NO3)2?6H2O
(34.4 mg, 0.1 mmol) to replace Co(NO3)2?6H2O. Large
Scheme 1 Molecular structure of ligands.
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quantities of light yellow-block crystals were obtained and the
crystals were filtered off, washed with quantities of distilled
water, and dried under ambient conditions. Yield of the
reaction was ca. 54% based on the H2L ligand. Anal. calcd for
C33H28CdN4O5: C, 58.89%, H, 4.19%, N, 8.32%; found: C,
58.74%, H, 4.23%, N, 8.26%. IR (KBr, cm21): 3437(m), 2363(w),
1674(w), 1589(s), 1538(m), 1393(s), 1316(m), 1222(m), 1179(m),
1075(w), 1009(w), 851(w), 809(w), 779(w), 703(w), 672(w),
629(w), 525 (w).
SYNTHESIS OF {[ZNL(BIBP)]?DMA?(H2O)2}n (4). A mixture of
Zn(NO3)2?6H2O (29.7 mg, 0.1 mmol), H2L (33.3 mg, 0.1 mmol)
and bibp (28.6 mg, 0.1 mmol) was dissolved in 8 mL DMA–H2O
(1 : 1, v/v). The final mixture was placed in a Parr Teflon-lined
stainless steel vessel (15 mL) under autogenous pressure and
heated at 100 uC for three days. Large quantities of colorless-
block crystals were obtained and the crystals were filtered off,
washed with distilled water, and dried under ambient
conditions. Yield of the reaction was ca. 63% based on the
H2L ligand. Anal. calcd for C42H40ZnN6O7: C, 62.57%, H,
5.00%, N, 10.42%; found: C, 62.65%, H, 5.06%, N, 10.46%. IR
(KBr, cm21): 3446(w), 3130(w), 2360(m), 1685(s), 1592(s),
1525(m), 1508(m), 1407(s), 1312(m), 1270(w), 1173(s), 1109(s),
1011(m), 952(m), 846(m), 786(m), 690(w), 557(w), 521(w),
463(w).
1650(m), 1593(s), 1553(m), 1488(m), 1394(s), 1310(s), 1221(m),
1139(m), 1014(m), 865(m), 845(w), 781(w), 694(w), 545(w),
447(w).
X-Ray crystallography
Single crystals of 1–5 were prepared in single crystal form.
X-Ray crystallographic data of 1–5 were collected at room
temperature using epoxy-coated crystals mounted on glass
fiber. All measurements were made on a Bruker Apex Smart
CCD diffractometer with graphite-monochromated Mo Ka
radiation (l = 0.71073Å). The structures of complexes 1–5 were
solved by direct methods and the non-hydrogen atoms were
located from the trial structure and then refined anisotropi-
cally with SHELXTL using a full-matrix least-squares proce-
dures based on F2 values.20a The hydrogen atom positions
were fixed geometrically at calculated distances and allowed to
ride on the parent atoms. The distribution of peaks in the
channels of 3–5 were chemically featureless to refine using
conventional discrete-atom models. To resolve these issues,
the contribution of the electron density by the remaining water
molecule was removed by the SQUEEZE routine in PLATON.20b
Relevant crystallographic data are presented in Table 1, while
the selected bond lengths and angles are given in the ESI
(Table S1, ESI ).
3
SYNTHESIS OF {[COL(BPYB)0.5]?(H2O)2}n (5). Co(NO3)2?6H2O (29.1
mg, 0.1 mmol), H2L (33.3 mg, 0.1 mmol) and bpyb (23.2 mg,
0.1 mmol) were added to water (2 mL) and DMF (6 mL). The
final mixture was placed in a Parr Teflon-lined stainless steel
vessel (15 mL) under autogenous pressure and heated at 100
uC for three days. Large quantities of black-block crystals were
obtained and the crystals were filtered off, washed with
distilled water, and dried under ambient conditions. Yield of
the reaction was ca. 67% based on the H2L ligand. Anal. calcd
for C28H23CoN2O6: C, 62.00%, H, 4.27%, N, 5.16%; found: C,
62.03%, H, 4.35%, N, 5.21%. IR (KBr, cm21): 3442(m), 3072(w),
Results and discussion
Crystal structure of {ZnL(bimx)0.5}n (1)
The crystal structure determination reveals that compound 1
crystallizes in the triclinic crystal system of P1. The asymmetric
unit contains one Zn(II) cation, half of the bimx ligand, one
deprotonated L ligand (Fig. 1a). In an asymmetric unit, the two
carboxylate groups of the L ligand take different coordination
modes, one carboxylate group takes
a
bismonodentate
Table 1 Crystallographic data and structure refinement details for complexes 1–5
Compound
1
2
3
4
5
Formula
Formula weight
C
27H20N3O4Zn
C33H28N4O5Co
619.52
C30H21N3O4Cd
599.92
C38H27N5O4Zn
683.04
C28H19N2O4Co
506.38
515.83
Crystal system
Space group
a/Å
b/Å
c/Å
Triclinic
P1
Monoclinic
C2/c
28.3656(16)
11.4712(6)
18.2929(10)
90.00
102.8760(10)
90.00
8
Monoclinic
C2/c
28.676(4)
11.7344(15)
17.820(3)
90.00
101.202(2)
90.00
8
Monoclinic
P2(1)/n
11.972(3)
12.043(4)
27.792(8)
90.00
99.959(4)
90.00
4
3947(2)
1.150
0.663
1408.0
Monoclinic
C2/c
25.0837(11)
8.7814(4)
22.6654(10)
90.00
91.8530(10))
90.00
8
9.6317(6)
10.0666(6)
13.2230(8)
100.8150(10)
108.2140(10)
102.0740(10)
2
1145.87(12)
1.495
1.112
a (u)
b (u)
c (u)
Z
V (Å3)
5802.6(5)
1.418
0.641
5882.1(15)
1.355
0.779
4989.9(4)
1.348
0.724
Dc (g cm23
)
m(Mo Ka) (mm21
F(000)
)
530.0
2568
2416.0
2080
Total, unique data
Rint
8428, 5687
0.0544
18 291, 6652
0.0968
17 472, 6802
0.0392
26 485, 6922
0.1043
13 679, 4399
0.1374
Observed data [I . 2s(I)]
Nref, Npar
R1, wR2 (I . 2s(I)) in-
4617
5079
4540
5397
3601
5687, 316
0.0390/0.0894
0.948
6652, 390
0.0428/0.1180
1.005
6578, 343
0.0448/0.1301
1.020
6922, 433
0.0756/0.2145
1.084
4399, 316
0.0492/0.1376
1.073
S
Min. and max. residual density/e Å23
20.618, 0.522
20.448, 0.427
20.843, 1.379
21.213, 1.182
20.558, 0.690
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Fig. 1 (a) Coordination environment of the Zn(II) ions in 1. The hydrogen atoms are omitted for clarity (30% ellipsoid probability). Symmetry codes: #1 = 1 2 x, 2 2 y, 1
2 z; #2 = 1 + x, 1 + y, 1 + z; #3 = 2x, 1 2 y, 2z; #4 = 2x, 1 2 y, 1 2 z; #5 = 21 + x, 21 + y, 21 + z. (b) Views of the 1D beaded chain formed by the deprotonated L
ligands and Cd cations. (c) A perspective view of the 2D framework. (d) The simplified ABAB fashion of compound 1.
coordination mode to bridge two Zn centers while the other
carboxylate group adopts a monodentate coordination mode
(Scheme 2a). Zn(II) is four-coordinated, bound by three O
atoms from three L ligands and one N atom from the bimx
ligands to form a distorted tetrahedron geometry. Neighboring
zinc atoms are also joined into a [Zn2(CO2)4] binuclear unit
with a two-membered ring by the bridging carboxylates. The
Zn–Zn distance across the binuclear unit is 3.347(4) Å. Two L
ligands connect two [Zn2(CO2)4] units to form a M2L2 ring, and
each [Zn2(CO2)4] unit binds to two adjacent units through the
four L ligands to form a 1D beaded chain (Fig. 1b). Finally, the
chains are connected by the bimx ligands to form a 2D sheet
(Fig. 1c). The sheets are stacked in ABAB fashion (Fig. 1d). The
Zn–O bond distances vary in the range of 1.9389(14)–
1.9872(14) Å and the Zn–N bond distance is 2.0012(21) Å. All
these distances fall in the normal range found in other Zn
complexes.21,22
Crystal structure of {[CoL(4,49-bipy)]?DMF}n (2)
The crystal structure determination reveals that compound 2
crystallizes in the monoclinic crystal system of C2/c. The
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Scheme 2 Crystallographically established coordination modes of the carboxylic groups in compounds 1–5.
asymmetric unit contains one Co(II) cation, one 4,49-bipy
ligand, one deprotonated L ligand and one DMF molecule,
which is omitted for clarity (Fig. 2a). In the asymmetric unit,
the two carboxylate groups of the L ligand take different
coordination modes, one carboxylate group takes a bismono-
dentate coordination mode to bridge two Co centers while the
other carboxylate group adopts a chelating in bidentate mode
(Scheme 2b). Co(II) is six-coordinate, bound by four O atoms
from three L ligands and two N atoms from two 4,49-bipy
ligands. Neighboring cobalt atoms are also joined into a
[Co2(CO2)4] binuclear unit. The Co–Co distance across the
binuclear unit is 4.086 Å. Two L ligands connect two
[Co2(CO2)4] units to form a M2L2 ring, and each [Co2(CO2)4]
unit binds to two adjacent units through the four L ligands to
form a 1D beaded chain. The chain can be simplified as the
chain of a diagonal parallelogram (Fig. 2b). Finally, the chains
are connected by the 4,49-bipy ligands to form a 2D sheet
(Fig. 2c). The sheets are stacked in ABAB fashion and form a
3D framework (Fig. 2d). The Co–O bond distances vary in the
range of 2.0196(14)–2.2024(15) Å, and the Co–N bond
distances vary in the range of 2.1760(18)–2.1805(18) Å. All
these distances fall in the normal range found in reported Co
complexes.
Crystal structure of {[CdL(4,49-bipy)]?DMF}n (3)
X-Ray analysis reveals that the asymmetric unit of compound 3
consists of one crystallographically independent cadmium(II)
cation, one deprotonated L22 ligand, one 4,49-bipy ligand and
one free DMF molecule. The DMF molecule was removed by
the SQUEEZE routine in PLATON. As shown in Fig. 3a, the L
ligand adopts the similar coordination mode (Scheme 2c), in
which one carboxylate group takes a m3-chelating–bridging
tridentate mode while the other carboxylate group adopts a
chelating bidentate mode. The Cd center is seven-coordinated
by five oxygen atoms belonging to four separated L ligands as
well as two nitrogen atoms from 4,49-bipy ligands with the Cd–
O distances ranging from 2.313(3) Å to 2.546(3) Å and Cd–N
distances ranging from 2.330(3) Å to 2.341(4) Å, which can be
compared with values reported previously.23 Two L ligands
connect two [Cd2(CO2)4] units to form a M2L2 ring, and each
[Cd2(CO2)4] unit binds to two adjacent units through the L to
form a 1D beaded chain (Fig. 3b). The Cd–Cd distance across
the binuclear unit measures 3.863 Å. Then, the 4,49-bipy
ligands join all infinite 1D chains into a 2D layer (Fig. 3c). The
layers are stacked in ABAB fashion, which is similar to
compound 2, and simplified as in the Fig. 3d. As we know,
the transition metal centers are bridged by flexible dicarbox-
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Fig. 2 (a) Coordination environment of the Co(II) ions in compound 2. The hydrogen atoms and lattice DMF molecules are omitted for clarity (30% ellipsoid
probability). Symmetry codes: #1 = 0.5 2 x, 1.5 2 y, 2 2 z; #2 = 20.5 + x, 1.5 2 y, 20.5 + z; #3 = 1 2 x, y, 2.5 2 z; #4 = x, 21 + y, z; # 5 = 0.5 + x, 1.5 2 y, 0.5 + z. (b)
Views of the beaded 1D chain formed by the L ligands and Co cations. (c) A perspective view of the 2D framework. (d) The simplified 3D structure of compound 2.
ylate ligands to generate 1D chains, and 2D layers, which are
pillared by rigid ligands into higher dimensional frameworks.
The pimelic acid generates 2D layers, and the L acid is inclined
to generate 1D chains.24a The result implies that the subtle
difference in co-ligand has a great influence on the structure of
the complexes.
reported work.25 The L ligands connect Zn atoms to form a 1D
chain, which is composed of ‘‘V-shapes’’ (Fig. 4b). Then the
bibp ligands join all infinite 1D chains into a 3D framework
(Fig. 4c). With the topological viewpoint, the Zn can be viewed
as 4-connecting nodes and the L ligands as linkers, the
framework adopts the cds topology, a 4-connected {65?8} net,
as shown in Fig. 4d. According to Blatov’s classification,26 the
interpenetration can be classified as type Class IIIa, Z = 4[2 6
2] (Zt = 2; Zn = 2).
Crystal structure of {[ZnL(bibp)]?DMA?(H2O)2}n (4)
Compound 4 crystallizes in a monoclinic space group P2(1)/n,
as shown in Fig. 4a, the asymmetric unit contains one Zn(II)
ion, one deprotonated L ligand, one 4,49-bibp ligand. The
Zn(II) ion is coordinated by two carboxylic O atoms from two L
ligands and two nitrogen atoms from two bibp ligands to form
a distorted tetrahedron geometry. In addition, there are one
DMA and two H2O molecules removed by the SQUEEZE
routine in PLATON. In an asymmetric unit, the two carboxylate
groups of the L ligands take the same coordination modes.
They all take a monodentate coordination mode (Scheme 2d).
The bond lengths of Zn1–N2 and Zn1–N5#2 are 2.048(4) and
2.012(4) Å, respectively, and the Zn1–O1 distance is 1.943(4) Å.
They are reasonably compared with the values in previously
Crystal structure of {[CoL(bpyb)0.5]?(H2O)2}n (5)
The crystal structure determination reveals that complex 5
crystallizes in the monoclinic crystal system of C2/c. In the
asymmetric unit, it contains an independent Co(II) cation, an L
ligand, a half of a bipb ligand and two H2O molecules (Fig. 5a).
The coordination geometry for each Co atom is a distorted
octahedron with four O atoms from four different ligands
forming the middle plane. One nitrogen atom and one Co
atom are in the axial position of the distorted octahedron. In
this compound, the H2L ligand acts as a ‘‘V-shape’’ link and
the carboxylate group adopts a bismonodentate coordination
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Fig. 3 (a) Coordination environment of the Cd(II) ions in 3. The hydrogen atoms are omitted for clarity (30% ellipsoid probability). Symmetry codes: #1 = x, 21 + y, 21
+ z; #2 = x, 2y, 1 2 z; #3 = x, y, 21 + z; #4 = 0.5 + x, 0.5 2 y, 0.5 + z; #5 = 2x, y, 0.5 2 z; #6 = 0.5 2 x, 0.5 2 y, 1 2 z; #7 = 0.5 2 x, 20.5 2 y, 1 2 z; #8 = x, 21 + y, z; #9 =
20.5 + x, 0.5 2 y, 20.5 + z. (b) View of the 1D chain formed by the L ligands and Cd cations. (c) A perspective view of the 2D framework. (d) The simplified formation
of ABAB fashion.
mode (Scheme 2e) to bridge two Co centers to form paddle-
wheel [Co2(CO2)4] clusters, the distance of Co–Co is 2.745(7) Å.
The Co–O bond lengths are in the range of 2.017(2)–2.095(2) Å
and the Co–N bond length is 2.062(2) Å, which are all similar
to those values found in reported complexes.24b Each L22
ligand links two SBUs to form a 2D layered network (Fig. 5b).
Then the bpyb ligands link the layers to further generate an
infinite 3D framework (Fig. 5c). The dinuclear Co(II) SBUs can
be regarded as 6-connected nodes with the L ligands acting as
linkers. A topology analysis reveals that the structure can be
represented as the Schlafli symbol {44?610?8}, as displayed in
Fig. 5d.
For compound 1, there is not any weight loss before 430 uC,
because compound 1 has not free small molecules such as
H2O, DMF, DMA, CH3CN and so on in its system. So, it
possesses better thermal stability before 430 uC. Compounds 2
and 3 have similar structures so have similar thermal stability.
A weight loss is observed from 100 to 189 uC, which is
attributed to the loss of the free DMF molecules. Their
structures decompose quickly after 400 uC. For complex 4, a
weight loss of 15.37% (calcd 15.26%) is observed from 90 to
190 uC, which is attributed to the loss of the free DMA and H2O
molecules, and it decomposes quickly after 400 uC. For
complex 5, there is a weight loss of 6.64% (calcd 6.97%) in
the extent from 80 to 100 uC, which is ascribed to the loss of
two H2O molecules. The TGA of the complexes are shown in
PXRD and TG results
To confirm whether the crystal structures are truly representa-
tive of the bulk materials, PXRD experiments are carried out
for compounds 1–5. The PXRD experimental and computer-
simulated patterns of the corresponding complexes are shown
the ESI (Fig. S6).
3
Photochemical properties
During the past few years, the coordination polymers with d10
metal centers have been investigated for fluorescence proper-
ties with potential applications in photochemistry, chemical
sensors, and light-emitting diodes (LEDs).26b Compounds 1, 3
and 4 are insoluble in common organic solvents; therefore, the
in the ESI (Fig. S1–S5). They show that the synthesized bulk
3
materials and the measured single crystals are the same.
To estimate the stability of the coordination architectures,
the thermal behavior of complexes 1–5 were studied by TGA.
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Fig. 4 (a) Coordination environment of the Zn(II) ions in compound 4. The hydrogen atoms are omitted for clarity (30% ellipsoid probability). Symmetry codes: #1 =
0.5 + x, 1.5 2 y, 0.5 + z; #2 = 21 + x, 1 + y, z; #3 = 1 + x, 21 + y, z; #4 = 20.5 + x, 1.5 2 y, 20.5 + z. (b) View of the ‘‘V-shapes’’ 1D chain structure formed by the L
ligands and Zn cations along the b axis. (c) View of the 3D framework. (d) Schematic representation of the {65?8} topological net with 4-fold interpenetrating
architecture.
luminescent properties of the free ligands L, 4,49-bipy, bibp
and bimx and complexes 1, 3 and 4 are investigated in the
solid state and at room temperature, as depicted in Fig. 6. The
emission peaks of the L, 4,49-bipy, bibp and bimx ligands were
observed with wavelengths at 423 nm for L (lex = 304 nm), 370
nm for 4,49-bipy (lex = 317 nm), 438 nm for bibp (lex = 321 nm)
and 420 nm for bimx (lex = 352 nm), which could be attributed
to the p*–p or p*–n transitions of the ligands. The emission
peaks were at 415 nm in compound 1 (lex = 298 nm), 457 nm
in compound 3 (lex = 306 nm) and 412 nm in compound 4 (lex
= 362 nm). Compound 1 exhibits an intense emission with a
maximum at 415 nm upon excitation at 298 nm. They are
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Fig. 5 (a) Coordination environment of the Co(II) ions in compound 5. The hydrogen atoms omitted for clarity (30% ellipsoid probability). Symmetry codes: #1 = 2x,
2y, 2z; #2 = x, 1 2 y, 20.5 2 z; #3 = 2x, 21 + y, 0.5 2 z; #4 = 0.5 2 x, 21.5 2 y, 2z; #5 = 2x, 1 + y, 0.5 2 z; #6 = x, 1 2 y, 0.5 + z. (b) Views of the 2D net structure and
Co(II) ions along the c axis. (c) Views of the 3D framework along the b axis. (d) The {44?610?8} topology net.
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bibp and 4,49-bipy ligands show intense absorption peaks at
240–400 nm, which can be ascribed to p–p* and n–p*
transitions of the ligands. Energy bands of 2 and 5 from
500–600 nm, are assigned as d–d transitions of the corre-
sponding metal ions, while higher energy bands from 300 to
500 nm are assigned as probably being metal-to-ligand charge-
transfer (MLCT) transitions.29 The lower energy bands of
compounds 2 and 5 in the 600–900 nm range are owing to the
4
4
electronic transitions from T1g(F) to T2g(F).30
Magnetic properties
As observed in the crystal structure, the adjacent Co atoms in
complex 5 are bridged by carboxylate groups to form paddle-
wheel [Co2(CO2)4] clusters, thus its magnetic property is
interesting. Variable-temperature magnetic susceptibility mea-
surements were performed on a crystalline sample of 5 in the
temperature range of 1.8–300 K. The temperature dependence
of magnetic susceptibility data for 5 is shown in Fig. 7 in the
form of xMT and xM vs T plots (xM is the molar magnetic
susceptibility for two Co(II) ions). At room temperature, xMT is
3.921 cm3 K mol21, which is slightly greater than the expected
value of 3.75 cm3 K mol21 for two isolated high-spin Co(II) ions
(g = 2 and S = 3/2) per formula because of the prominent
orbital contribution arising from the 4T1g ground state of
Co(II). Upon cooling, the xMT rapidly decreases and practically
vanishes at T , 50 K, indicating antiferromagnetic coupling
between the Co ions.31 The xM value slowly increases from
0.01307 cm3 K mol21 at 300 K to 0.01349 cm3 K mol21 at 229
K, but decreases to 0.00734 cm3 K mol21 at 40 K, which is
attributed to the spin–orbit coupling. Then the xM value
rapidly increases to 0.04302 cm3 K mol21 at 2 K, which implies
that there is a small amount of impurities in compound 5. The
magnetic susceptibility data were fitted assuming that the
carboxylate bridges of the Co(II) ions form an isolated spin–
dimer system.
Fig. 6 Solid-state photoluminescent spectra of 1, 3 and 4 and the correspond-
ing ligands at room temperature.
similar to those of the free L ligand so can be ascribed to the
p*–p or p*–n transitions within the molecular orbital mani-
folds of the imidazolyl of bimx moieties and phenyl rings of L
moieties. The emission bands of compound 3 are also similar
to those of the free L ligand but show a red shift of 34 nm as
compared with that of the L ligand, which may be assigned to
ligand to metal change transfer (LMCT).27 Compound 4
exhibits mission characteristics similar to those of the L
ligand but shows an obvious blue shift of 26 nm as compared
with that of the L ligand. The phenomenon is probably caused
by a change in the HOMO and LUMO energy levels of the
deprotonated L22 anions and neutral ligands coordinating to
the metal centers, a charge-transfer transition between ligands
and metal centers, and a joint contribution of the intraligand
transitions or charge-transfer transitions between the coordi-
nated ligands and the metal centers.28 In addition, the blue
shift is also attributed to the non-coplanar ligands and the
different distortion among the benzene rings, which prevent
the efficient electron transfer in compound 4.
Conclusions
All UV-vis absorption spectra for the three free ligands and
complexes 2 and 5 were recorded in reflectance mode in solid
In summary, we have successfully synthesized and character-
ized five new compounds by the self-assembly of H2L,
4,49-bipy, bibp, bpyb, bimx ligands, and different bivalent
metal salts under different solvothermal conditions. The
research explains that changing the central metals and the
solvents may play an important role to construct the
structural diversities of coordination polymers. In addition,
the research provides a new example of the H2L ligand for
the design of novel frameworks. The flexible H2L ligand can
provide more possibilities for the construction of unusual
topology structures and microporous coordination polymers.
Subsequent works will be focused on the structures and
properties of a series of coordination compounds con-
structed by the H2L ligand with other auxiliary ligands and
metal ions to prevent interpenetrating architecture to get
good properties and porous structures of coordination
polymers.
state at room temperature, as shown in ESI (Fig. S7). The L,
3
Fig. 7 Temperature dependence of xMT and xM vs. T for 5.
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Acknowledgements
This work was supported by grants from the Natural Science
Foundation of China (no. 91022011; 20971065; 21021062) and
National Basic Research Program of China (2010CB923303).
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