Topological evolution and photoluminescent properties of a series of divalent zinc-based metal-organic frameworks tuned via ancillary ligating spacers

Article abstract of DOI:10.1016/j.jssc.2013.01.004

The combination of divalent zinc ions, 4-(4-carboxybenzamido)benzoic acid and exo-bidendate bipyridine ligands gave rise to a series of new MOFs: [ZnL(bipy)]·DMF·H₂O (1), [ZnL(bpe)]·1.5H ₂O (2), [ZnL(bpa)]·4H₂O (3) and [ZnL(bpp)]·1.75H₂O (4) (MOF=metal-organic framework, bipy=4,4′-bipyridine, bpe=trans-1,2-bis(4-pyridyl)ethylene, bpa=1,2-bis(4-pyridinyl)ethane, bpp=1,3-bis(4-pyridinyl)propane, H ₂L=4,4′-(carbonylimino)dibenzoic acid). Fine tune over the topology of the MOFs was achieved via systematically varying the geometric length of the second ligating bipyridine ligands. Single-crystal X-ray analysis reveals that complex 1 has a triply interpenetrated three-dimensional (3D) framework with elongated primitive cubic topology, whereas isostructural complexes 2 and 3 each possesses a 6-fold interpenetrated diamondiod 3D framework. Further expansion of the length of the bipyridine ligand to bpp leads to the formation of 4, which features an interesting entangled architecture of 2D→3D parallel polycatenation. In addition, the thermogravimetric analyses and solid-state photoluminescent properties of the selected complexes are investigated.

Full text of DOI:10.1016/j.jssc.2013.01.004

Journal of Solid State Chemistry 200 (2013) 265–270
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Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Topological evolution and photoluminescent properties of a series of divalent
zinc-based metal–organic frameworks tuned via ancillary ligating spacers
Xiao-Min Lian, Wen Zhao, Xiao-Li Zhao n
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, 3663 North Zhongshan Road,
Shanghai 200062, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The combination of divalent zinc ions, 4-(4-carboxybenzamido)benzoic acid and exo-bidendate
bipyridine ligands gave rise to a series of new MOFs: [ZnL(bipy)] ꢀ DMF ꢀ H2O (1), [ZnL(bpe)] ꢀ 1.5H2O
(2), [ZnL(bpa)] ꢀ 4H2O (3) and [ZnL(bpp)] ꢀ 1.75H2O (4) (MOF¼metal-organic framework, bipy¼4,40-
bipyridine, bpe¼trans-1,2-bis(4-pyridyl)ethylene, bpa¼1,2-bis(4-pyridinyl)ethane, bpp¼1,3-bis(4-
pyridinyl)propane, H2L¼4,40-(carbonylimino)dibenzoic acid). Fine tune over the topology of the MOFs
was achieved via systematically varying the geometric length of the second ligating bipyridine ligands.
Single-crystal X-ray analysis reveals that complex 1 has a triply interpenetrated three-dimensional (3D)
framework with elongated primitive cubic topology, whereas isostructural complexes 2 and 3 each
possesses a 6-fold interpenetrated diamondiod 3D framework. Further expansion of the length of the
bipyridine ligand to bpp leads to the formation of 4, which features an interesting entangled
architecture of 2D-3D parallel polycatenation. In addition, the thermogravimetric analyses and
solid-state photoluminescent properties of the selected complexes are investigated.
Received 19 October 2012
Received in revised form
4 January 2013
Accepted 6 January 2013
Available online 31 January 2013
Keywords:
Acylamide functionality
MOF
Bipyridine
4-(4-carboxybenzamido)benzoic acid
Photoluminescent property
& 2013 Elsevier Inc. All rights reserved.
1. Introduction
ligands on the formation of MOFs will be explored. The synthetic
strategy takes advantage of four factors: (1) the combination of
Intense interest in the chemistry of metal-organic frameworks
(MOFs) stems from their topological aesthetics and intriguing
potential applications as new functional solid materials for gas
storage, separation, heterogeneous catalysis, etc [1]. Most of these
applications are highly associated with the porosity of MOFs. One of
the main concerns regarding porosity of MOFs is catenation, which
will mitigate the free volume and reduce the pore size. Nevertheless,
the existence of catenation is not always negative, as their occur-
rence will contribute much to the structural diversity and intrigue of
MOFs [2]. Moreover, catenation can lead to materials with enhanced
properties or functions, such as superhard materials [3], magnetic
materials [4], and materials with high stability or enhanced adsorp-
tion capacity [5]. A conventional strategy of using long exo-
multidentate ligands has been successful to construct polycatenated
networks. Recently, a handful of new protocols such as liquid-phase
epitaxial growth, templated synthesis, manipulation of reaction
conditions have been applied to manipulate the catenation behavior
of MOFs and thus improve their properties [6]. In this report, we
address tune of catenation by incorporation of the exo-bidentate
bipyridine ligands 4,40-bipyridine (bipy), trans-1,2-bis(4-pyridy-
l)ethylene (bpe), 1,2-bis(4-pyridinyl)ethane (bpa), 1,3-bis(4-pyridi-
nyl)propane (bpp) into the Zn2þ–H2L system, anticipating that
systematic investigation of the effects of the pyridyl-based spacer
multicarboxylate ligands and multipyridyl ligands incorporates the
virtues of different functional groups to control the resulting
architecture by changing one of the ligands [7]; (2) the acylamide
group possesses both hydrogen-bonding donor and acceptor sites
and has been extensively employed in the construction of MOFs
with guest-accessible functional organic sites for catalysis inside the
channels [8]; (3) both theoretical studies and experimental observa-
tions indicate that decoration of MOFs with polar acylamide groups
can significantly enhance the CO2 binding ability and selectivity of
MOFs. This will improve their properties for practical applications
such as natural gas purification and greenhouse gas control [9]. (4) It
is well documented that exo-bidendate nitrogen ligands such as
bipy, bpe, bpa and bpp can coordinate to metal ions as spacer
ligands [10]. Execution of the synthetic procedure shown in
Scheme
1 yielded the following four complexes, [ZnL(bi-
py)] ꢀ DMF ꢀ H2O (1), [ZnL(bpe)] ꢀ 1.5H2O (2), [ZnL(bpa)] ꢀ 4H2O (3)
and [ZnL(bpp)] ꢀ 1.75H2O (4), whose structures and photolumines-
cent properties will be presented.
2. Experimental
2.1. Materials and physical measurements
All chemicals and reagents of analytical grade were commer-
cially available and used without further purification. 4,40-(car-
bonylimino)dibenzoic acid (H2L) was synthesized according to
n Corresponding author. Fax: þ86 21 62233179.
E-mail address: xlzhao@chem.ecnu.edu.cn (X.-L. Zhao).
0022-4596/$ - see front matter & 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jssc.2013.01.004

266
X.-M. Lian et al. / Journal of Solid State Chemistry 200 (2013) 265–270
Scheme 1.
the reported methods [11]. NMR spectra were obtained using a
Bruker Avance V 400M instrument. Elemental analyses were
determined on a Vario ELIII Elemental Analyzer. The IR spectra
were recorded on a Bruker TENSOR 27 spectrometer in the 4000–
500 cmꢁ1 range. Thermogravimetric analyses (TGA) were carried
out on a Netzsch STA 449 F3 instrument with a heating rate of
10 1C minꢁ1 under N2 atmosphere. Powder X-ray diffraction
(PXRD) data were recorded using a Rigaku (D/Max-Ultima IV)
2.4. Synthesis of [ZnL(bpa)] ꢀ 4H2O (3)
When the procedure for 1 was repeated using bpa instead of
bipy, colorless block-like crystals of 3 were obtained in 78% yield
(based on H2L). IR: 3446(w), 2928(w), 1660(vs), 1604(vs),
1561(w), 1526(s), 1431(w), 1381(vs), 1321(s), 1255(s), 1175(m),
1141(w), 1099(m), 1069(m), 1030(m), 1018(m), 900(w), 861(s),
833(s), 816(s), 783(s), 733(s), 701(m), 663(m).
diffractometer equipped with Cu-K
a radiation, with a step size
and a scan speed of 0.021 minꢁ1 and 51 minꢁ1, respectively.
Simulated PXRD patterns were calculated with the Mercury
program using the single crystal data [12]. Solid-state photolu-
minescent spectra of complexes 1–4 were measured on a Varian
Cary Eclipse fluorescence spectrometer.
2.5. Synthesis of [ZnL(bpp)] ꢀ 1.75H2O (4)
The synthetic procedure of 1was repeated using bpp instead of
bipy. Colorless block-like crystals were obtained in 69% yield
(based on H2L). Anal. Calcd for C28H26.5ZnN3O6.75 (Mr¼578): C,
58.14; H, 4.62; N, 7.26. Found: C, 57.96; H, 4.82; N, 7.16. IR:
3444(w), 1943(m), 1613(vs), 1529(s), 1434(w), 1368(vs), 1322(s),
1255(m), 1177(m), 1140(m), 1070(m), 1031(m), 1017(m), 900(w),
880(w), 858(m), 812(m), 784(s), 733(s), 701(w), 656(w), 626(w).
2.2. Synthesis of [ZnL(bipy)] ꢀ DMF ꢀ H2O (1)
A mixture of H2L (20.00 mg, 0.07 mmol), bipy (10.93 mg,
0.07 mmol) and Zn(NO3)2 ꢀ 6H2O (20.86 mg, 0.07 mmol) in 4 mL
DMF/H2O (1:7) was placed in a 15 mL Teflon-lined autoclave and
subjected to solvothermal condition at 140 1C for 48 h after
ultrasonic treatment and then cooled to room temperature (cool-
ing rate 0.1 1C minꢁ1). Colorless needle-shaped crystals were
collected by filtration and washed with DMF to give 1 (32 mg,
yield: 77% based on H2L). Anal. Calcd for C28H26ZnN4O7
(Mr¼595.91): C, 56.43; H, 4.40; N, 9.40. Found: C, 56.41; H,
4.27; N, 9.46. IR: 3482(w), 3074(w), 1662(s), 1604(s), 1541(s),
1396(vs), 1322(s), 1258(m), 1220(w), 1179(m), 1148(m), 1098(s),
1069(m), 1046(m), 1017(s), 860(s), 820(vs), 783(vs), 729(vs),
632(m), 609(s).
2.6. X-ray crystallography
Selected crystals were used for data-collection on a Bruker
SMART ApexII diffractometer equipped with graphite-
˚
monochromatic Mo K
in a nitrogen stream. Frames were collected at 0.51 intervals in
a radiation (l¼0.71073 A) at 173 K cooled
j
and for 30 s per frame such that a hemisphere of data was
o
collected. Raw data collection and refinement were done using
SMART. Data reduction was performed using SAINTþ. Absorption
corrections were applied using the SADABS program. For 1, the
structure was solved by Patterson method. For 2, 3 and 4, the
structures were solved by direct method. All the structures were
then refined by full-matrix least-squares on F2 with anisotropic
displacement using SHELX-97 [13]. Non-hydrogen atoms were
refined with anisotropic displacement parameters during the final
cycles. All the hydrogen atoms attached to carbon atoms were
placed in calculated positions and refined using the riding model.
Potential solvent accessible area and void space were calculated
using the PLATON/SOLV [14]. For 1, the uncoordinated DMF
molecules are disordered and were treated using the split-atom
models. The coordinated L2ꢁ in 2 was treated using the split-atom
models with half occupancies for each set to obtain the appro-
priate thermal parameters. Crystal data and structure refinement
details are summarized in Table 1.
2.3. Synthesis of [ZnL(bpe)] ꢀ 1.5H2O (2)
Complex 2 was synthesized in a similar manner to 1 except
that bpe was used instead of bipy. Colorless block-like crystals
were isolated in 84% yield (based on H2L). IR: 3481(w), 2990(w),
1655(w), 1613(vs), 1524(m), 1509(m), 1432(w), 1373(vs),
1318(s), 1254(s), 1175(w), 1140(m), 1099(w), 1069(w), 1027(s),
977(m), 860(w), 837(s), 812(w), 778(s), 729(s), 657(w).

X.-M. Lian et al. / Journal of Solid State Chemistry 200 (2013) 265–270
267
3. Results and discussions
Zn–O and Zn–N bond lengths fall into the range of 1.930(5)–
II
˚
˚
1.935(5) A and 2.039 (5)–2.047 (4) A, respectively. The Zn atom
serves as node with L2ꢁ and bpe ligands as linkers to construct a
3D structure with a diamondoid topology (for complex 2, Fig. 2c;
3.1. Structural description of [ZnL(bipy)] ꢀ DMF ꢀ H2O (1)
˚
˚
Solvothermal reaction of H2L with Zn(NO3)2 ꢀ 6H2O and bipy in
DMF–H2O system resulted in the formation of complex 1. Single-
crystal structure analysis reveals that 1 crystallize in monoclinic space
group P21/c. The asymmetric unit of 1 contains one ZnII atom, one
bipy, one L2ꢁ, one uncoordinated DMF and one lattice water
molecule. As shown in Fig. 1a, ZnII adopts a slightly distorted
octahedral geometry, being coordinated by four carboxylate oxygen
atoms from three L2ꢁ ligands (the Zn–O distances are in the ranges of
for complex 3, Fig. 3c). A cavity with the pore 31 A ꢂ 20 A is
generated by an independent equivalent diamondoid cage (for
complex 2, Fig. 2b; for complex 3, Fig. 3b). The potential voids are
large enough to generate a 6-fold interpenetrating 3D architec-
ture with a diamondoid topology (for complex 2, Fig. 2d; for
complex 3, Fig. 3d). It is noteworthy that only 15.8% of the
effective free volume in the desolvated 2 is left due to the 6-
fold interpenetration. For 3, the pore void space is 25.8% after six-
fold interpenetration. It is noteworthy that complex 3 still
˚
˚
2.038(3) A and 2.277(3) A) and two nitrogen atoms from two bipy
˚
˚
˚
˚
molecules (Zn1–N1¼2.132(3) A, Zn1–N2¼2.140(3) A). Four carbox-
ylate groups from four symmetry-related L2ꢁ ligands coordinate to
two ZnII centers to form the dinuclear Zn2(COO)4 secondary building
unit (SBU), which are further bridged by L2ꢁ to form a (4,4) rhomboid
grid layer. Within each layer, the rhomboid windows have dimen-
exhibits a 1D rectangle channels about 8.6 A ꢂ 9.2 A along the b
axis despite the 6-fold interpenetration.
3.3. Structural description of [ZnL(bpp)] ꢀ 1.75H2O (4)
˚
˚
sions of 19.02 A ꢂ 19.02 A with angles of 82.361 and 97.641 (defined
by Zn ꢀ ꢀ ꢀ Zn distances and Zn ꢀ ꢀ ꢀ Zn ꢀ ꢀ ꢀ Zn angles) (Fig. 1b). Further
pillaring of the layers through bipy ligands generates a 3D pillar-layer
architecture, and the Zn/Zn distance through the bipy ligand is
Continuous increase of the length and flexibility of the ancil-
lary ligand was achieved when bpp was used instead of bpe and
complex 4 with 2D -3D parallel polycatenation architecture was
harvested. Complex 4 crystallizes in monoclinic space group P21/
c, the crystallographically independent ZnII is four-coordinated in
a tetrahedral geometry being coordinated by two carboxylate
oxygen atoms and two pyridyl nitrogen atoms (Fig. 4a). Further
extension of the [ZnN2O2] tetrahedron through the bpp and L2ꢁ
form a 4-coordinated highly corrugated layer structure with 44-
sql topology (Fig. 4b). The rhomboid voids with dimensions of
˚
11.35 A (Fig. 1c). The topology of 1 can be best described as an
elongated primitive cubic net. A 3-fold interpenetrating framework is
observed due to the existence of large channels (Fig. 1c and d). The
total accessible volume after removal of the guest DMA and water
molecules is 26.9% using the PLATON/VOID routine.
˚
˚
12 A ꢂ 17 A and angles of 971 and 901 (defined by Zn ꢀ ꢀ ꢀ Zn
distance and Zn ꢀ ꢀ ꢀ Zn ꢀ ꢀ ꢀ Zn angles) within each layer allow
interpenetration between adjacent layers to occur. The most
intriguing feature of 4 is the 2D-3D parallel polycatenation.
The 44-sql layers stack with an ABAB sequences, and each of these
equivalent layers is polycatenated with the adjacent two parallel
layers (Fig. 4c). To the best of our knowledge, 2D-3D parallel
polycatenation based on 44-sql layers is rare and only few
examples have been reported [15].
3.2. Structural description of [ZnL(bpe)] ꢀ 1.5H2O (2) and
[ZnL(bpa)] ꢀ 4H2O (3)
Further expansion of the length of the exo-bidendate bipyr-
idine ligand to bpe and bpa leads to the formation of complexes 2
and 3, respectively. X-ray analysis showed 2 and 3 are virtually
isostructural though both crystallize in different space groups (for
complex 2, triclinic, P1 ; for complex 3, orthorhombic, Pccn). The
following discussion on the structural aspect will mainly focus on
complex 2. Single-crystal X-ray analysis reveals that the asym-
metric unit of crystal 2 consists of one ZnII, two halves bpe and
two halves L2ꢁ ligands. Each ZnII ion is in a slightly distorted
tetrahedral geometry, being coordinated by two carboxylate
oxygen atoms from two L2ꢁ and two nitrogen atoms from two
bpe molecules (for complex 2, Fig. 2a; for complex 3, Fig. 3a). The
3.4. Thermal stability analysis and powder X-ray diffraction (PXRD)
analysis
Thermogravimetric analyses (TGA) are performed on crystal-
line samples to examine the thermal stability (Figs. S1–S4). For 1,
Table 1
Crystallographic data of complexes 1–4.
Compound
1
2
3
4
Empirical Formula
C28H26N4O7Zn
595.87
C27H22N3O6.5Zn
557.86
C27H29N3O9Zn
604.91
C28H26.5N3O6.75Zn
578.41
M [g molꢁ1
]
Crystal system
Space group
Monoclinic
P21/c
Triclinic
Orthorhombic
Pccn
Monoclinic
P21/c
¯
P1 1
9.6217(5)
28.6285(1)
10.4801(5)
8.3235(4)
11.6874(6)
13.3742(7)
23.2651(1)
15.2345(9)
16.8340(1)
9.4166(5)
25.7859(1)
11.9616(6)
˚
a [A]
˚
b [A]
˚
c [A]
a
b
g
[1]
90
80.737(2)
90
90
111.3760(1)
85.828(2)
90
108.6140(1)
[]
˚
[]
90
83.364(2)
90
90
˚
V [A3]
2688.2(2)
1273.53(1)
5966.5(6)
2752.5(2)
Z
4
2
8
4
r
m
calcd. [g cmꢁ3
(Mo-K
) [mmꢁ1
]
1.465
1.417
1.329
1.385
a
]
0.968
1.008
0.876
0.941
F(0 0 0)
range, 1
Rint
1220
556
2448
1180
2.20–25.01
1.55–25.00
2.00–25.01
1.96–25.01
y
0.0345
0.0248
0.0587
0.0317
Final R indices [I42
R indices (all data)
s(I)]
R1¼0.0563, wR2¼0.1221
R1¼0.0607, wR2¼0.1238
R1¼0.0793, wR2¼0.2207
R1¼0.0880, wR2¼0.2324
R1¼0.1275, wR2¼0.2552
R1¼0.1475, wR2¼0.2726
R1¼0.0575, wR2¼0.1436
R1¼0.0743, wR2¼0.1594

268
X.-M. Lian et al. / Journal of Solid State Chemistry 200 (2013) 265–270
Fig. 1. Crystal structure of [ZnL(bipy)] ꢀ DMF ꢀ H2O (1): (a) the coordination environment of ZnII in 1; (b) Single ZnL layer in 1; (c) pillared 3D structure of 1; (d) Space-filling
showing of the 3-fold interpenetrating framework of 1.
Fig. 2. Crystal structure of [ZnL(bpe)] ꢀ 1.5H2O (2): (a) coordination environment around ZnII; (b) the single diamondoid cage in 2. Ligand bpe and L are represented in red
and gray, respectively; (c) a single 3D framework of 2; (d) schematic diagram of the 6-fold interpenetration in 2.
the weight loss of 15.17% between 20 1C and 220 1C represented
elimination of the water and DMF molecules of crystallization
(15.28% loss calcd). For 2, the weight loss of 4.45% up to 180 1C
corresponds to the removal of water molecules (cacld 4.84%). No
further weight loss is observed between 180 1C and 320 1C, and
decomposition begins at 320 1C. For 3, dehydration occurred
between 20 1C and 120 1C, as indicated by a total weight loss of
11.89% (cacld 11.91%). Rapid elimination of the organic

X.-M. Lian et al. / Journal of Solid State Chemistry 200 (2013) 265–270
269
Fig. 3. Crystal structure of [ZnL(bpa)] ꢀ 4H2O 3: (a) coordination environment around ZnII in 3; (b) single diamondoid cage in 3; (c) a single 3D framework of 3;
(d) schematic diagram of the 6-fold interpenetration in 3; (e) space-filling showing of the 1D rectangle channels in 3 after 6-fold interpenetration.
Fig. 4. Crystal structure of [ZnL(bpp)] ꢀ 1.75H2O 4: (a) coordination environment of ZnII in 4; (b) corrugated layer structure of 4; (c) schematic illustration of the parallel
polycatenation in 4.
components occurred above 300 1C. For 4, expulsion of the water
molecules happened in the range of 25 1C and 100 1C (obsd 5.62%,
cacld 5.45%), the mass remained largely stable until 380 1C.
PXRD analyses are carried out to check the structural identity.
For 1–4, the measured PXRD pattern closely matches the one
simulated from single-crystal diffraction data, indicating the
phase purity (Figs. S5–S8).
and photochemistry [16]. The luminescent properties of com-
plexes 1–4 as well as the free H2L ligand were investigated in the
solid state at room temperature. Complexes 1 and 4 exhibit very
weak fluorescent emission under experimental conditions,
whereas 2 and 3 exhibit emission enhancement (Fig. 5).
The main emission peak of the free H2L at 433 nm
(
lex¼334 nm) may be ascribed to the
[17]. Complexes 2, show emission peaks at 464 nm
lex¼365 nm) and 453 nm lex¼320 nm), respectively. The
p
n-p or pn- n transitions
3
3.5. Photoluminescent properties
(
(
enhancement of luminescence for the two complexes compared
with the free H2L under the same conditions may mainly
originate from coordination of the ligand to a zincII ion, which
effectively increases the rigidity of the ligand and reduces thermal
Photoluminescent properties of metal-containing comp-
lexes have attracted much attention due to their potential
applications in electroluminescent display, chemical sensors,

270
X.-M. Lian et al. / Journal of Solid State Chemistry 200 (2013) 265–270
development foundation for financial support (Grant No.
2008CG31) and Shanghai Rising-Star Program (10QA1402000).
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ligand [18]. Besides, in comparison with the free ligand, red-shifts
of about 31 nm and 20 nm are found for 2 and 3, respectively,
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This work was supported by the National Natural Science
Foundation of China (NSFC No. 20801018), Shanghai education
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