Structural diversity of four new metal-organic frameworks with a curved tetracarboxdiimide dicarboxylic acid

Article abstract of DOI:10.1039/c3ce41805g

Four new metal-organic frameworks (MOFs), {[Co₂(L) ₂(DMF)₃]·6.5DMF·5H₂O} _n (1), {[Cu(L)(H₂O)]·2DMA}_n (2), {[Zn₂(L)(DMF)₂(HCOO)₂] ·3DMF·2H₂O}_n (3), and {[Cd ₂(L)₂(DMF)(H₂O)(μ₂-OH ₂)₂]·3.5DMF·2H₂O}_n (4) (H₂L = N-phenyl-N′-phenylbicyclo[2.2.2]oct-7-ene-2,3,5,6- tetracarboxdiimide dicarboxylic acid; DMA = N,N-dimethylacetamide; DMF = N,N-dimethylformamide) have been synthesized under solvothermal conditions. MOFs 1, 2 and 3 display various interesting two-dimensional (2D) structures, including 2D lattice structure, 2-fold interpenetrated 2D structure, and 2D tube-based network. MOF 4 features an interesting two-fold interpenetrated 3D structure possessing a 6-connected pcu network with the point symbol of {4 ¹²·6³}. Photoluminescent properties of MOFs 3 and 4 have been investigated in the solid state at room temperature.

Full text of DOI:10.1039/c3ce41805g

CrystEngComm
View Article Online
View Journal | View Issue
PAPER
Structural diversity of four new metal–organic
frameworks with a curved tetracarboxdiimide
dicarboxylic acid†
Cite this: CrystEngComm, 2014, 16,
834
*
Huimin Li, Jingmin Zhou, Wei Shi, Xuejing Zhang, Zhenjie Zhang, Meng Zhang
*
and Peng Cheng
Four new metal–organic frameworks (MOFs), {[Co2(L)2(DMF)3]·6.5DMF·5H2O}n (1), {[Cu(L)(H2O)]·2DMA}n (2),
{[Zn2(L)(DMF)2(HCOO)2]·3DMF·2H2O}n (3), and {[Cd2(L)2(DMF)(H2O)(μ2-OH2)2]·3.5DMF·2H2O}n (4)
(H2L = N-phenyl-N′-phenylbicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxdiimide dicarboxylic acid; DMA =
N,N-dimethylacetamide; DMF = N,N-dimethylformamide) have been synthesized under solvothermal
conditions. MOFs 1, 2 and 3 display various interesting two-dimensional (2D) structures, including 2D
lattice structure, 2-fold interpenetrated 2D structure, and 2D tube-based network. MOF 4 features an
interesting two-fold interpenetrated 3D structure possessing a 6-connected pcu network with the point
symbol of {412·63}. Photoluminescent properties of MOFs 3 and 4 have been investigated in the solid
state at room temperature.
Received 7th September 2013,
Accepted 23rd October 2013
DOI: 10.1039/c3ce41805g
www.rsc.org/crystengcomm
acid,11 4-hydroxypyridine-2,6-dicarboxylic acid,12 thiophene-
2,5-dicarboxylic acid13 and furan-2,5-dicarboxylic acid,14
Introduction
Metal–organic frameworks (MOFs) have received great atten-
tion during the past decades owing to not only their various
intriguing structural topologies but also their great potentials
as functional materials in magnetism,1 catalysis,2 gas storage/
separation,3,4 ion exchange,5 optical properties,6,7 and so on.
Although the design and synthesis of such materials are highly
influenced by many factors, such as the coordination trend of
metal centers, the bridging modes of the ligands, as well as reac-
tion conditions, judicious selection of organic bridging ligands
with appropriate symmetry is still an effective approach to con-
struct MOFs with unique structures and properties. Among
numerous organic ligands, carboxylic acid ligands, such as
1,4-benzenedicarboxylate and 1,3,5-benzenetricarboxylate,8,9
are commonly used in the construction of MOFs due to the
coordination diversity of carboxylic group. Based on our previ-
ous studies, it is obvious that the coordination modes of
ligands with specific symmetry are key factors to the final
structures and properties of the products. For example, a
series of porous MOFs with high symmetry were successfully
obtained using dicarboxylic acid with C2-like symmetry such
as pyridine-3,5-dicarboxylic acid,10 pyridine-2,6-dicarboxylic
which provided an effective “symmetry approach” for the
construction of MOFs.
As a continuous work, our attention was paid to a type of
curved carboxylic acids with high symmetry as ligand to design
and construct new MOFs. N-Phenyl-N′-phenylbicyclo[2.2.2]oct-
7-ene-2,3,5,6-tetracarboxdiimide tetracarboxylic acid is an inter-
esting curved and directional ligand in MOFs chemistry.15 We
have designed and constructed a new type of MOF with this
ligand showing unusual interpenetrated cationic (MOF–A+) and
anionic (MOF–B−) nets, as well as ion exchange and lumines-
cent properties.15a N-Phenyl-N′-phenylbicyclo[2.2.2]oct-7-ene-
2,3,5,6-tetracarboxdiimide dicarboxylic acid (H2L) (Scheme 1),
similar to the above ligand, was still unexplored in this field.
H2L has specific symmetry within two benzoic acid groups
linked at their 4-position by a long curved acid dianhydride,
which can be a good candidate for the design and construc-
tion of diverse MOFs that deserves further exploration. In this
contribution, we report the synthesis and crystal structures of
four new MOFs with H2L. Reactions of H2L with four transi-
tion metal ions generated {[Co2(L)2(DMF)3]·6.5DMF·5H2O}n (1),
{[Cu(L)(H2O)]·2DMA}n (2), {[Zn2(L)(DMF)2(HCOO)2]·3DMF·2H2O}n
(3), and {[Cd2(L)2(DMF)(H2O)(μ2-OH2)2]·3.5DMF·2H2O}n (4).
The structures of these compounds are significantly influenced
by the reaction conditions, such as solvents, metal salt species
and ligand–metal ratio. MOFs 1, 2, and 3 display different 2D
structures, including 2D lattice structure, two-fold interpenetrated
2D lattice structure, and 2D tube-based structure. It is noted
that 2D planes of 2 are 2-fold interlinked with each other to
Department of Chemistry, Key Laboratory of Advanced Energy Materials
Chemistry (MOE), and Synergetic Innovation Center of Chemical Science and
Engineering (Tianjin), Nankai University, Tianjin 300071, PR China.
E-mail: shiwei@nankai.edu.cn, pcheng@nankai.edu.cn
† Electronic supplementary information (ESI) available: PXRD spectra and TGA
spectra. CCDC 951691–951694. For ESI and crystallographic data in CIF or
other electronic format see DOI:10.1039/c3ce41805g
834 | CrystEngComm, 2014, 16, 834–841
This journal is © The Royal Society of Chemistry 2014

View Article Online
CrystEngComm
Paper
(vs), 1299 (m), 1191 (s), 1104 (m), 1015 (w), 770 (s), 725 (m),
699 (m), 602 (m).
Synthesis of {[Cu(L)(H2O)]·2DMA}n (2)
The mixture of H2L (0.10 mmol, 0.0486 g), CuCl2·6H2O
(0.25 mmol, 0.0606 g), 0.5 mL ethanol and 3 mL DMA was
sealed in a 25 mL Teflon-lined autoclave. The mixture was
heated to 80 °C for 3 days, and then cooled to room tempera-
ture at a rate of 2 °C h−1. Blue rhombic block crystals were
obtained (yield: 55%, based on Cu). Element analysis (%) found
(calcd.) for C34H36CuN4O11 (2), C 54.87 (55.16), H 5.06 (4.90),
N 8.03 (7.67); IR (KBr, ν/cm−1): 3471 (m), 2945 (m), 1707 (vs),
1599 (vs), 1512 (s), 1406 (vs), 1303 (w), 1191 (s), 1016 (m),
837 (w), 800 (s), 769 (vs), 735 (s), 595 (m), 538 (w), 472 (w), 424 (w).
Scheme 1 The structure of H2L.
provide an unusual interpenetrated double layer. 2D tube-
based structure of 3 is also rare in coordination chemistry.
In addition, MOF
4 presents an interesting two-fold
interpenetrated 3D framework. The luminescent properties
of 3 and 4 were also studied.
Experimental section
Materials and instrumentation
Synthesis of {[Zn2(L)(DMF)2(HCOO)2]·3DMF·2H2O}n (3)
The mixture of H2L (0.10 mmol, 0.0486 g), Zn(ClO4)2·6H2O
(0.10 mmol, 0.0372 g), LiOH·H2O (0.2 mmol, 0.0839 g) and
3 mL DMF was sealed in a 25 mL Teflon-lined autoclave.
The mixture was heated to 80 °C for 3 days, and then cooled
to room temperature at a rate of 2 °C h−1. Colorless prism
crystals were obtained (yield: 60% based on Zn). Element
analysis (%) found (calcd.) for C43H57Zn2N7O19 (3), C 46.58
(46.67), H 5.09 (5.19), N 9.20 (8.86); IR (KBr, ν/cm−1): 3457
(br), 1713 (vs), 1659 (s), 1607 (m), 1558 (m), 1508 (w), 1338
(s), 1300 (w), 1194 (m), 1102 (m), 1018 (w), 843 (w), 770 (m),
728 (w), 600 (w).
All the reagents and solvents employed were commercially
available and used without further purification. Elemental
analyses (C, H, and N) were performed on a Perkin-Elmer
240 CHN elemental analyzer. IR spectra were recorded in the
range 400–4000 cm−1 on a Bruker TENOR 27 spectrophotome-
ter using KBr pellets. Powder X-ray diffraction measurements
were recorded on a D/Max-2500 X-ray diffractometer using
Cu Kα radiation. The luminescent spectra were measured
on a Varian Cary Eclipse fluorescence spectrophotometer.
Thermal analyses (under nitrogen atmosphere, heating rate
of 10 °C min−1) were carried out in a Labsys NETZSCH TG
1
209 Setaram apparatus. The H-NMR spectrum was measured
Synthesis of {[Cd2(L)2(DMF)(H2O)(μ2-OH2)2]·3.5DMF·2H2O}n (4)
on a Mercury Vx-300 NMR spectrometer.
The mixture of H2L (0.10 mmol, 0.0486 g), CdCl2·6H2O
(0.25 mmol, 0.0729 g), 0.5 mL methanol and 3 mL DMF was
sealed in a 25 mL Teflon-lined autoclave. The mixture was
heated to 80 °C for 3 days, and then cooled to room tempera-
ture at a rate of 2 °C h−1. Colorless block crystals were obtained
(yield: 42% based on Cd). Element analysis (%) found (calcd.)
for C65.5H73.5Cd2N8.5O25.5, C 48.72 (48.78), H 4.53 (4.59), N 7.87
(7.38); IR (KBr, ν/cm−1): 3459 (br), 2934 (w), 1772 (w), 1715 (vs),
1661 (vs), 1604 (vs), 1558 (s), 1508 (m), 1390 (vs), 1299 (m),
1192 (s), 1102 (m), 929 (w), 771 (s), 728 (m), 408 (w).
Synthesis of H2L
A mixture of 20 mmol (2.7400 g) 4-aminobenzoic acid and
10 mmol (2.4800 g) bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic
acid dianhydride was added into 100 mL acetic acid. Then the
mixture was heated to reflux for 12 h. White powder was
obtained by filtration, washing, and drying. H2L was used with-
out further purification. Element analysis (%) found (calcd.)
for H2L (C26H18O8N2), C 63.85 (64.20), H 4.02 (3.73), N 5.78
(5.76). IR bands (KBr, ν/cm−1) for H2L: 2937 (m), 1709 (vs), 1607
(m), 1513 (m), 1381 (s), 1285 (m), 1178 (s), 858 (w), 798 (m),
766 (m), 717 (m). 1H-NMR (300 MHz, DMSO-d6), δ (ppm): 3.45
(s, 2H), 3.52 (s, 1H), 6.31 (t, 1H), 7.30 (d, 2H) 7.99 (d, 2H).16
X-ray crystallography
Data collections of 1–4 were performed on an Oxford Super-
nova TM diffractometer with graphite-monochromated Mo-Kα
radiation (λ = 0.71073 Å) using ω-scan technique at 150 K. The
structures were solved by direct methods and refined with the
full matrix least-squares technique based on the SHELXS-97
and SHELXL-97 programs.17 Anisotropic thermal parameters
were assigned to all non-hydrogen atoms. The hydrogen atoms
of the organic ligand were generated geometrically; the hydro-
gen atoms of the water molecules were located from difference
maps and refined with isotropic temperature factors.
Synthesis of {[Co2(L)2(DMF)3]·6.5DMF·5H2O}n (1)
The mixture of H2L (0.10 mmol, 0.0486 g), CoCl2·6H2O
(0.25 mmol, 0.0595 g), LiOH·H2O (0.2 mmol, 0.0839 g) and
2 mL DMF was sealed in a 25 mL Teflon-lined autoclave.
After being heated at 80 °C for 3 days, it was cooled to room
temperature at a rate of 2 °C h−1. Red block crystals were
obtained (yield: 33% based on Co). Element analysis (%) found
(calcd.) for C80.5H108.5Co2N13.5O30 (1), C 51.64 (51.67), H 5.92
(5.84), N 9.89 (10.10); IR (KBr, ν/cm−1): 3371 (br), 2935.26 (w),
1773 (m), 1711 (vs), 1661 (s), 1602 (s), 1556 (s), 1508 (m), 1387
The contributions of disordered solvent molecules in 1–4
were treated as diffuse using the squeeze procedure in Platon.18
Details for structural analysis are summarized in Table 1.
This journal is © The Royal Society of Chemistry 2014
CrystEngComm, 2014, 16, 834–841 | 835

View Article Online
Paper
CrystEngComm
Table 1 Data collection and processing parameters for 1–4
Compounds
1
2
3
4
Formula
Fw
Temp, K
C61H53Co2N7O19
1305.96
293(2)
C34H36CuN4O11
740.21
293(2)
C43H57Zn2N7O19
1106.77
293(2)
C65.5H73.5Cd2N8.5O25.5
1612.65
293(2)
Crystal system
Space group
Triclinic
P1
Orthorhombic
Ibam
Orthorhombic
Pcca
Monoclinic
P2/c
¯
a, Å
b, Å
c, Å
α, °
11.4985(3)
21.2760(6)
21.4387(6)
77.071(2)
80.672(2)
88.411(2)
5044.0(2)
2
0.860
0.377
0.0304
0.922
11.744(2)
19.878(4)
36.094(7)
90
90
90
8426(3)
8
0.889
0.553
0.0954
11.7133(3)
18.7995(5)
24.1755(6)
90
90
90
5223.5(2)
8
1.227
0.965
0.0480
15.1796(7)
15.6453(5)
16.9845(15)
90
119.218(5)
90
3520.3(4)
2
1.242
0.668
0.0444
1.069
0.0867, 0.2439
0.1062, 0.2622
2.03/−1.11
β, °
γ, °
V, Å3
Z
Dc, g cm−3
μ, mm−1
Rint
GOF on F2
R1, wR2 [I > 2σ(I)]
R1,wR2(all data)
1.044
1.053
0.0565, 0.1683
0.0756, 0.1788
1.436/−0.592
0.0793, 0.2198
0.1248, 0.2488
0.536/−0.349
0.0629, 0.1713
0.0812, 0.1834
1.03/−0.71
Δρmax/min(e Å−3
)
pH value, metal salts species, temperature, and time of reac-
tion, etc.) can influence the reaction process and the final
products. Solvent as template is one of the keys to the con-
struction of MOFs because solvent can act as space-filling
molecules.19 For MOFs 1, 3 and 4, DMF solvents behave as
not only coordinated molecules but also crystal lattice mole-
cules. For MOF 2, one water molecule coordinates with Cu2+
Results and discussion
Synthesis and structures
MOFs 1–4 were generated by solvothermal reaction of H2L
with different transition metal salts (CoII, CuII, ZnII and
CdII salts), and the synthetic strategies of 1–4 were presented
in Scheme 2. In general, the reaction variables (solvent,
Scheme 2 Synthesis schematic diagrams for 1–4.
836 | CrystEngComm, 2014, 16, 834–841
This journal is © The Royal Society of Chemistry 2014

View Article Online
CrystEngComm
Paper
and free DMA molecules act as space-filling solvents. pH
value is another important factor to construct MOFs. Without
LiOH·H2O, 2D two-fold interpenetrated 2 and 3D two-fold
interpenetrated 4 were obtained. The difference of transition
metal ions also plays an essential role in the construction of
the compounds. The diverse connection modes of the sec-
ondary building units (SBUs) are due to the coordination
trend of the central metal ions, and further leads to the dif-
ferent structures. For 1, two six-coordinated CoII ions are
three-fold connected by carboxyl groups to form a dinuclear
secondary building units (SBUs) and adjacent dinuclear
Co-SBUs are linked through L2− to generate 2D lattice structure.
For 2, each dinuclear CuII paddle-wheel SBU is connected with
adjacent four CuII SBUs through L2− to generate a 2D rhombic
layer as well. However, different from 1, MOF 2 presents an inter-
esting interpenetrating network due to the diversity of metal
ions and pH value. For 3, four-coordinated and six-coordinated
ZnII ions are alternately connected with each other through car-
boxyl groups to form a 1D chain and these chains are
connected by L2− generating a 2D structure with 1D tube-shape
channels. For 4, CdII ions adopt six-coordinated and eight-
coordinated modes forming a trinuclear Cd3 SBU and these
Cd3 SBUs in a line are linked by μ2-OH2 to CdII chains, which
are further connected with each other by L2− from different
directions to generate a two-fold interpenetrated 3D structure.
Scheme 3 The coordination modes of H2L in 1–4.
(O9 and O15A), and other three oxygen atoms from DMF
molecules. The Co–O bond lengths are in the range of
1.995(2)–2.228(3) Å. Co1 and Co2 are three-fold bridged by
two (κ1-κ1)-carboxylic groups (O3 and O4, O15A and O16B)
and one (κ1-κ2-μ2)-carboxylic group (O9 and O10) to form
a dinuclear SBU. These Co-SBUs are connected through
(κ1-κ1)-(κ2)-μ3-L2− along b axis and (κ1-κ1)-(κ1-κ2-μ2)-μ4-L2−
along c axis to generate a 2D lattice structure along a axis
(Fig. 1b). The 2D planes are pile-up of dislocations to form a
3D supramolecular structure through weak intermolecular
interaction of π⋯π dislocated stacking (Fig. 1c).
Crystal structure of {[Co2(L)2(DMF)3]·6.5DMF·5H2O}n (1)
¯
1 belongs to triclinic space group P1. There are two crystallo-
graphically independent six-coordinated CoII ions (Co1 and
Co2), two L2−, three DMF molecules in the asymmetric
unit (Fig. 1a). Co1 coordinates with six oxygen atoms from
three carboxylic oxygen atoms (O1A, O2A, and O4) of
(κ1-κ1)-(κ2)-μ3-L2− (Scheme 3a) and other three carboxylic oxy-
gen atoms (O9, O10, and O16B) of (κ1-κ1)-(κ1-κ2-μ2)-μ4-L2−
(Scheme 3b). Co2 adopts a slightly distorted octahedral coor-
dination geometry with three carboxylic oxygen atoms from
one (κ1-κ1)-(κ2)-μ3-L2− (O3) and two (κ1-κ1)-(κ1-κ2-μ2)-μ4-L2−
Crystal structure of {[Cu(L)(H2O)]·2DMA}n (2)
MOF 2 crystallizes in orthorhombic space group Ibam. As
shown in Fig. 2, there are one crystallographically independent
CuII ions, one L2− and one water molecules in the asymmetric
unit. CuII ion is five-coordinated with four carboxylic oxygen
atoms (O1, O1A, O2B, and O2C) from (κ1-κ1)-(κ1-κ1)-μ4-L2−
(Scheme 3c) and one water molecule (Fig. 2a). The Cu–O bond
lengths range from 1.940(3) to 2.131(6) Å. Two adjacent
CuII ions are linked with four (κ1-κ1)-carboxylic groups to
form binuclear SBUs of square paddlewheels, which are fur-
ther linked by (κ1-κ1)-(κ1-κ1)-μ4-L2− to build a 2D plane with
rhombic lattices (Fig. 2b). Each 2D layer has an undulating
net with rhombic windows, in which each dinuclear CuII
paddle-wheel SBU connects with four neighboring SBUs
by the curved ligands. It is notable that, different from 1,
two (4,4) nets are interlinked with each other to generate a
parallel interpenetrated 2D layer (Fig. 2c). Although the
Fig. 1 (a) The coordination environment of MOF 1 (H atoms and
solvent molecules were omitted for clarity), (b) the 2D lattice structure
along a-axis, (c) the packing diagram along a-axis, (d) the packing
diagram along b-axis, (e) the packing diagram along c-axis.
This journal is © The Royal Society of Chemistry 2014
CrystEngComm, 2014, 16, 834–841 | 837

View Article Online
Paper
CrystEngComm
Fig. 3 (a) The coordination environment of MOF 3 (H atoms and solvent
molecules were omitted for clarity), (b) the 3D supermolecular network.
tetrahedral coordination geometry. The formate groups were
generated by the decomposition of DMF.21 Zn2 is six-
coordinated with two carboxylic oxygen atoms (O3A and O3B)
from two (κ1-κ1)-(κ1-κ1)-μ4-L2−, two formate oxygen atoms (O1
and O1B) and two oxygen atoms (O10 and O10A) from two
DMF molecules to form octahedral coordination geometry.
The Zn–O bond lengths vary from 1.957(5) to 2.138(5) Å.
Zn1 and Zn2 are connected by two (κ1-κ1)-carboxylic oxy-
gen atoms and (κ1-μ2)-formate oxygen atoms forming a
binuclear SBU. Adjacent binuclear SBUs are connected by
(κ1-κ1)-carboxylic groups and formate groups to form 1D
chains, which are further linked by L2− ligands to a 2D layer.
The weak interactions of π⋯π stacking between adjacent
layers generate a 3D supermolecular network with 1D tube-
shape channel along a axis with the dimensions of ca.
9.8 Å × 15.3 Å, which is produced by two L2− curved in oppo-
site directions connected with Zn2 (Fig. 3b). The channels
are occupied by water and DMF molecules. PLATON18 analy-
sis reveals that the structure contains voids of 1229.5 Å3,
which represents 23.1% volume per unit cell with the
removal of water and DMF molecules. As far as we know,
2D tube-based plan structure is still unexplored, although
2D square-grid structure and MOFs with 1D tube-shape
channel are known.22
Fig. 2 (a) The coordination environment of MOF 2 (H atoms and
solvent molecules were omitted for clarity), (b) the 2D rhombic plane
viewed along a-axis, (c) two-fold interpenetration viewed along the
b-axis, and (d) the staking diagram along c-axis.
formation of structurally interpenetrated networks is hardly
prospective and is obtained rather accidentally, such a par-
allel interpenetrated 2D layer is interesting and rather rare.
The reported parallel interpenetrated 2D compounds with
(4,4) nets tend to adopt a single metal ion as a node to
connect with four ligands,20 while 2 adopts dinuclear CuII
paddle-wheel SBUs linked with each other by four L2−
.
Though the main networks of MOFs 1 and 2 are similar, the
packing modes of the networks are totally different. In MOF 1,
each Co2 SBU is linked with four curved L2−, and the curved
L2− ligands along the same direction are bent consistently,
while the L2− along different directions are bent oppositely.
In MOF 2, the contrary is the case. L2− along the same direc-
tion linked to one Cu2 SBU are bent in opposite directions. As
a result, the 2D networks of 1 tend to pile-up of dislocations
(i.e. interdigitation) and those of 2 prefer to interpenetrate as
a double layer so that they can minimize the systematic
energy through optimal filling of the space. In addition,
MOFs 1 and 2 show two ways in which a crystal can maximize
its packing efficiency interdigitation and interpenetration.
It is also noted that interdigitation and interpenetration are
caused by different bent directions of the same ligand, which
is not reported up to date, to the best of our knowledge.
Crystal structure of {[Cd2(L)2(DMF)(H2O)(μ2-OH2)2]·3.5
DMF·2H2O}n (4)
MOF 4 crystallizes in monoclinic space group P2/c and
exhibits an interesting two-fold interpenetrating 3D structure.
There are two crystallographically independent CdII ions
(Cd1 and Cd2), one L2−, one DMF molecule, and three
water molecules in the asymmetric unit, as shown in Fig. 4a.
Cd1 is coordinated with eight oxygen atoms from two
(κ2)-carboxylic groups (O7A, O8A, O7B, and O8B) and two
(κ1-κ2-κ1-μ3)-carboxylic groups (O1, O2, O1A, and O2A) of
(κ2)-(κ1-κ2-κ1-μ3)-μ4-L2− (Scheme 3d), and the coordination
geometry of Cd1 ion can be viewed as a distorted trigonal
dodecahedron. Cd2 is six-coordinated adopting octahedral
coordination geometry with two carboxylic oxygen atoms
(O1 and O2A) from (κ2)-(κ1-κ2-κ1-μ3)-μ4-L2−, two μ2-OH2
molecules (O9 and O9A), one water molecule, and one DMF
molecule. The Cd–O bond lengths are in the range of
2.276–2.543 Å. Cd1 is connected with two Cd2 by two
Crystal structure of {[Zn2(L)(DMF)2(HCOO)2]·3DMF·2H2O}n (3)
Single crystal X-ray analyses reveal that 3 crystallizes in ortho-
rhombic space group Pcca. As shown in Fig. 3a, there are two
crystallographically independent ZnII ions (Zn1 and Zn2), one
L2−, two DMF and two HCOO− in the asymmetric unit. Zn1 is
four-coordinated with two carboxylic oxygen atoms (O5 and
O5A) from two (κ1-κ1)-(κ1-κ1)-μ4-L2− (Scheme 3c) and two for-
mate oxygen atoms (O1 and O1A), forming slightly distorted
(κ1-κ2-κ1-μ3)-carboxylic groups forming
a trinuclear Cd3
SBU, and adjacent trinuclear SBUs are linked by two μ2-OH2
838 | CrystEngComm, 2014, 16, 834–841
This journal is © The Royal Society of Chemistry 2014

View Article Online
CrystEngComm
Paper
are well in agreement with the simulated data, demonstrating
the phase purity of the compounds.
The thermal stabilities of 1–4 were measured by TGA
in N2 atmosphere from 25 to 800 °C (Fig. S2, ESI†). For 1,
a weight loss of 41.83% from 25 to 239.5 °C was observed,
corresponding to the loss of three coordinated DMF mole-
cules, five water molecules and six and half DMF molecules
in the lattice (theoretical 41.90%). With increasing the tem-
perature to 400 °C, the structure began to decompose, illus-
trating the strong thermal stability of 1. For 2, a weight loss
of 23.35% from 25 to 340.5 °C was observed, corresponding
to the release of two free DMA (theoretical 23.54%), then the
framework decomposed upon further heating. For 3, the first
weight loss of 22.61% occurred in the temperature ranging
from 25 to 339.6 °C due to the loss of three lattice DMF
and two lattice water molecules (theoretical 22.99%), and
further heating led to the decomposition of ligands. MOF 4
displayed a weight loss of 18.21% between 25 °C and 213.0 °C,
which is in accordance with the loss of lattice solvent mole-
cules (3.5DMF and 2H2O, theoretical 18.07%). With increas-
ing the temperature to 268.3 °C, the second weight loss of
3.85%, which accords with the loss of three coordinated water
molecules (theoretical 3.35%). On further heating, sharp
weight loss was observed, indicating the decomposition of the
organic ligands.
Fig. 4 (a) The coordination environment of MOF 4 (H atoms and
solvent molecules were omitted for clarity), (b) 1D chain, (c) the 3D
framework, and (d) the two-fold interpenetrated structure.
atoms to an one-dimensional (1D) Cd3 chain (Fig. 4b). Fur-
thermore, 1D Cd3 chains are linked by (κ2)-(κ1-κ2-κ1-μ3)-μ4-L2−
along different directions into a beautiful three-dimensional
(3D) network. Two sets of such 3D networks are inter-
penetrated with each other by weak interactions of π⋯π stack-
ing to form a two-fold interpenetrated structure (Fig. 4c). In
order to simplify this complicated framework, the network
topology has been analyzed by the freely available computer
program TOPOS.23 If each trinuclear Cd3 SBU is considered as
a six-connected node which links with four ligands and
another two Cd3 SBUs by μ2-OH2, and all the ligands and
μ2-OH2 serve as bridging linkers, the structure can be consid-
ered as a 6-connected net named pcu (Fig. 5). The point symbol
of the topology can be expressed as {412·63}. Among the two-
fold interpenetrated structures based on 3D networks, MOFs
based on 6-connected octahedral nodes and linear linkers
are rarely observed.24
Luminescent properties
Although a lot of transition metal ions have been used to
construct MOFs, the Zn and Cd-based MOFs are the most
interested transition-metal-based luminescent MOFs. The d10
metal ions not only have various coordination numbers and
geometries, but also display luminescent properties when
coordinated with functional ligands.25 The photoluminescent
properties of MOFs 3 and 4 have been studied in the solid
state at room temperature, as shown in Fig. 6. The strongest
emission peak at 333 nm for H2L ligand is observed upon
excitation at 270 nm. This emission band can be attributed
to π*–π or π*–n transitions.26 Excitation of the as-synthesized
3 at 340 nm leads to the maximum emission peak at 408 nm.
Powder X-ray diffraction (PXRD) and thermal gravimetric
analyses (TGA)
To confirm the phase purity of the four new compounds,
PXRD patterns have been carried out at room temperature
(Fig. S1, ESI†). The peak positions of the experimental PXRD
Fig. 5 The two-fold interpenetrated topological diagram of 4 (Cd3 SBU:
6-connected node).
Fig. 6 The solid-state emission spectra of H2L, 3, and 4.
CrystEngComm, 2014, 16, 834–841 | 839
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
CrystEngComm
Upon excitation at 328 nm the maximum emission peaks of 4
are observed at 377 nm. On comparison with the free H2L
ligand, the maximum emission peak of 3 shows a red shift of
75 nm and that of 4 shows a red shift of 44 nm. Considering
that ZnII ions and CdII ions are difficult to oxidize or reduce
due to their d10 configuration, the emissions of MOFs 3 and
4 are neither metal-to-ligand charge transfer (MLCT) nor ligand-
to-metal charge transfer (LMCT) in nature,27 which are mainly
based on the luminescence of ligands.28 The photoluminescent
of 3 and 4 may originate from the intraligand π*–π or π*–n
transition of the H2L ligand that is modified by the ZnII and
CdII ions. Different coordination environments may be an
important factor on influencing different luminescent behav-
iours of 3 and 4.
Y. K. Seo, J. Kim, A. Vimont, M. Daturi, C. Serre and
G. Férey, Angew. Chem., Int. Ed., 2008, 47, 4144; (d)
D. N. Dybtsev, A. L. Nuzhdin, H. Chun, K. P. Bryliakov,
P. Konstantin, E. P. Talsi, V. P. Fedin and K. Kim, Angew.
Chem., 2006, 118, 930; (e) C. D. Wu, A. Hu, L. Zhang and
W. B. Lin, J. Am. Chem. Soc., 2005, 127, 8940; (f) C. D. Wu,
A. Hu, L. Zhang and W. Lin, J. Am. Chem. Soc., 2005, 127,
8940; (g) J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh,
Y. J. Jeon and K. Kim, Nature, 2000, 404, 982.
3 (a) T. M. McDonald, W. R. Lee, J. A. Mason, B. M. Wiers,
C. S. Hong and J. R. Long, J. Am. Chem. Soc., 2012, 134, 7056;
(b) P. S. Myunghyun, J. P. Hye, K. P. Thazhe and D. W. Lim,
Chem. Rev., 2012, 112, 782; (c) J. Kang, S. H. Wei and
Y. H. Kim, J. Am. Chem. Soc., 2010, 132, 1510; (d)
A. W. Thornton, K. M. Nairn, J. M. Hill, A. J. Hill and
M. R. Hill, J. Am. Chem. Soc., 2009, 131, 10662; (e) B. Kesanli,
Y. Cui, M. Smith, E. Bittner, B. Bockrath and W. Lin, Angew.
Chem., 2005, 117, 74; (f) B. L. Chen, M. Eddaoudi, S. T. Hyde,
M. O. Keeffe and O. M. Yaghi, Science, 2001, 291, 1021.
4 (a) C. Zlotea, R. Campesi, F. Cuevas, E. Leroy, P. Dibandjo,
C. Volkringer, T. Loiseau, G. Férey and M. Latroche, J. Am.
Chem. Soc., 2010, 132, 2991; (b) J. H. Luo, H. W. Xu, Y. Liu,
Y. H. Zhao, L. L. Daemen, C. Brown, T. V. Timofeeva,
S. Q. Ma and H. C. Zhou, J. Am. Chem. Soc., 2008, 130, 9626;
(c) X. S. Wang, S. Ma, P. M. Forster, D. Yuan, J. Eckert,
J. J. López, B. J. Murphy, J. B. Parise and H. C. Zhou, Angew.
Chem., Int. Ed., 2008, 47, 7263; (d) A. R. Millward and
O. M. Yaghi, J. Am. Chem. Soc., 2005, 127, 17998; (e)
J. L. C. Rowsell and O. M. Yaghi, Angew. Chem., Int. Ed.,
2005, 44, 4670; (f) D. Sun, Y. Ke, T. M. Mattox, A. O. Betty
and H. C. Zhou, Chem. Commun., 2005, 5447.
5 (a) W. G. Lu, L. Jiang, X. L. Feng and T. B. Lu, Inorg. Chem.,
2009, 48, 6997; (b) A. P. Nelson, D. A. Parrish,
L. R. Cambrea, L. C. Baldwin, N. J. Trivedi, K. L. Mulfort,
O. K. Farha and J. T. Hupp, Cryst. Growth Des., 2009, 9,
4588; (c) A. Nalaparaju, R. Babarao, X. S. Zhao and
J. W. Jiang, ACS Nano, 2009, 3, 2563; (d) K. L. Gurunatha,
S. Mohapatra, P. A. Suchetan and T. K. Maji, Cryst. Growth
Des., 2009, 9, 3844; (e) J. A. Zhao, L. W. Mi, J. Y. Hu,
H. W. Hou and Y. T. Fan, J. Am. Chem. Soc., 2008, 130,
15222; (f) S. A. Kozimor, B. M. Bartlett, J. D. Rinehart and
J. R. Long, J. Am. Chem. Soc., 2007, 129, 10672.
6 (a) X. Feng, J. S. Zhao, B. Liu, L. Y. Wang, S. Ng, G. Zhang,
J. G. Wang, X. G. Shi and Y. Y. Liu, Cryst. Growth Des., 2010,
10, 1399; (b) Y. W. Lin, B. R. Jian, S. C. Huang, C. H. Huang
and K. F. Hsu, Inorg. Chem., 2010, 49, 2316; (c) L. Zhang,
Y. Y. Li, Z. J. Qin, Q. P. Li, J. K. Cheng, J. Zhang and
Y. G. Yao, Inorg. Chem., 2008, 47, 8286; (d) C. A. Bauer,
T. V. Timofeeva, T. B. Settersten, B. D. Patterson, V. H. Liu,
B. A. Simmons and M. D. Allendorf, J. Am. Chem. Soc., 2007,
129, 7136.
7 (a) Q. Yue, Q. Sun, A. L. Cheng and E. Q. Gao, Cryst. Growth
Des., 2010, 10, 44; (b) L. Yan, Q. Yue, Q. X. Jia, G. Lemercier
and E. Q. Gao, Cryst. Growth Des., 2009, 9, 2984; (c) H. Ren,
T. Y. Song, J. N. Xu, S. B. Jing, Y. Yu, P. Zhang and
L. R. Zhang, Cryst. Growth Des., 2009, 9, 105; (d) X. L. Chen,
Conclusion
In summary, we have successfully synthesized four new
MOFs with an interesting curved dicarboxylic ligand. MOFs
1, 2, and 3 display various 2D structures, including 2D lattice
structure, two-fold 2D interpenetrated lattice, and tube-based
2D network, respectively. MOF 4 shows an interesting two-
fold interpenetrated 3D structure possessing a 6-connected
pcu topology with the point symbol of {412·63}. The differ-
ences in the reaction conditions have played an important
role on the structural diversity of 1–4. The luminescent mea-
surements of 3 and 4 indicate that different coordination
environments of d10 ions (ZnII or CdII) influence the lumines-
cent properties of the ligands. This work illustrates a promis-
ing approach to rational design and synthesis of MOFs with
long curved dicarboxylates ligands and more effort is being
focused on porous and functional MOFs with diverse struc-
tures based on this curved dicarboxylate ligand.
Acknowledgements
We thank the “973 program” (2012CB821702), the NSFC
(21373115 and 21331003) and MOE (20120031130001) for
financial support.
Notes and references
1 (a) D. Pierre and R. L. Jeffrey, Chem. Soc. Rev., 2011, 40,
3249; (b) K. Mohamedally, Chem. Soc. Rev., 2009, 38, 1353;
(c) N. W. Ockwig, O. Delgado-Friedrichs, M. O'Keeffe and
O. M. Yaghi, Acc. Chem. Res., 2005, 38, 176; (d) H. L. Gao,
B. Zhao, X. Q. Zhao, Y. Song, P. Cheng, D. Z. Liao and
S. P. Yan, Inorg. Chem., 2008, 47, 11057; (e) M. H. Zeng,
B. Wang, X. Y. Wang, W. X. Zhang, X. M. Chen and S. Gao,
Inorg. Chem., 2006, 45, 7069; (f) D. Sun, D. J. Collins, Y. Ke,
J. L. Zuo and H. C. Zhou, Chem.–Eur. J., 2006, 12, 3768; (g)
Y. X. Ke, D. J. Collins, D. F. Sun and H. C. Zhou, Inorg.
Chem., 2006, 45, 1897.
2 (a) Y. L. Jeong, K. F. Omar, R. John, A. S. Karl, T. N. SonBinh
and T. H. Joseph, Chem. Soc. Rev., 2009, 38, 1450; (b)
L. Q. Ma, A. Carter and W. B. Lin, Chem. Soc. Rev., 2009, 38,
1248; (c) Y. K. Hwang, D. Y. Hong, J. S. Chang, S. H. Jhung,
840 | CrystEngComm, 2014, 16, 834–841
This journal is © The Royal Society of Chemistry 2014

View Article Online
CrystEngComm
B. Zhang, H. M. Hu, F. Fu, X. L. Wu, T. Qin, M. L. Yang,
Paper
G. B. Michael, D. G. Mostafab and N. R. Chaudhuri, J. Solid
State Chem., 2008, 181, 457.
G. L. Xue and J. W. Wang, Cryst. Growth Des., 2008, 8, 3706;
(e) Y. Q. Wei, Y. F. Yu and K. C. Wu, Cryst. Growth Des.,
2008, 8, 2087.
21 (a) J. Juillard, Pure Appl. Chem., 1977, 49, 885; (b) M. Boča,
I. Svoboda, F. Renz and H. Fuess, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 2004, 60, 631; (c) H. Li, W. Shi,
K. Zhao, Z. Niu, X. Chen and P. Cheng, Chem.–Eur. J., 2012,
18, 5715.
22 (a) X. L. Zhao, J. M. Dou, D. Sun, P. P. Cui, D. F. Sun and
Q. Y. Wu, Dalton Trans., 2012, 41, 1928; (b) R. Q. Zou,
X. H. Bu and R. H. Zhang, Inorg. Chem., 2004, 43, 5382; (c)
B. Kumar, H. Yoshito and F. Makoto, Angew. Chem., Int. Ed.,
2002, 41, 3395.
8 (a) M. Dinca, A. F. Yu and J. R. Long, J. Am. Chem. Soc.,
2006, 128, 8904; (b) C. Serre, F. Millange, C. Thouvenot,
M. Nogues, G. Marsolier, D. Louer and G. Férey, J. Am.
Chem. Soc., 2002, 124, 13519.
9 (a) J. Zhang, T. Wu, S. M. Chen, P. Y. Feng and X. H. Bu,
Angew. Chem., Int. Ed., 2009, 48, 3486; (b) S. L. Xie, B. Q. Xie,
X. Y. Tang, N. Wang and S. T. Yue, Z. Anorg. Allg. Chem.,
2008, 634, 842; (c) C. Daiguebonne, N. Kerbellec, K. Bernot,
Y. Gérault, A. Deluzet and O. Guillou, Inorg. Chem., 2006, 45,
5399; (d) T. M. Reineke, M. Eddaoudi, M. O'Keeffe and
O. M. Yaghi, Angew. Chem., Int. Ed., 1999, 38, 2590.
10 (a) Y. H. Zhao, Z. M. Su, Y. M. Fu, K. Z. Shao, P. Li, Y. Wang,
X. R. Hao, D. X. Zhu and S. D. Liu, Polyhedron, 2008, 27,
583; (b) F. E. Jarrod, D. W. Rosa and E. Mohamed, Chem.
Commun., 2005, 16, 2095.
11 (a) L. L. Wen, D. B. Dang, C. Y. Duan, Y. Z. Li, Z. F. Tian and
Q. J. Meng, Inorg. Chem., 2005, 44, 7161; (b) B. Zhao,
X. Y. Chen, P. Cheng, D. Z. Liao, S. P. Yan and Z. H. Jiang,
J. Am. Chem. Soc., 2004, 126, 15394; (c) K. G. Suji and
K. B. Parimal, Inorg. Chem., 2003, 42, 8250.
12 (a) H. L. Gao, L. Yi, B. Zhao, X. Q. Zhao, P. Cheng, D. Z. Liao
and S. P. Yan, Inorg. Chem., 2006, 45, 5980; (b) B. Zhao,
H. L. Gao, X. Y. Chen, P. Cheng, W. Shi, D. Z. Liao, S. Y. Yan
and Z. H. Jiang, Chem.–Eur. J., 2006, 12, 149.
13 (a) B. L. Chen, K. F. Mok, S. C. Ng and G. B. D. Michael, New
J. Chem., 1999, 23, 877; (b) B. L. Chen, K. F. Mok, S. C. Ng
and G. B. D. Michael, Polyhedron, 1999, 18, 1211; (c)
W. Huang, D. Y. Wu, P. Zhou, W. B. Yan, D. Guo, C. L. Duan
and Q. J. Meng, Cryst. Growth Des., 2009, 9, 1362.
14 (a) H. H. Li, W. Shi, N. Xu, Z. J. Zhang, Z. Niu, T. Han and
P. Cheng, Cryst. Growth Des., 2012, 12, 260; (b) H. H. Li,
W. Shi, K. N. Zhao, Z. Niu, H. M. Li and P. Cheng, Chem.–
Eur. J., 2013, 19, 3358.
15 (a) Z. J. Zhang, W. Shi, Z. Niu, H. H. Li, B. Zhao, P. Cheng,
D. Z. Liao and S. P. Yan, Chem. Commun., 2011, 47, 425; (b)
K. L. Mulfort, O. K. Farha, C. D. Malliakas, M. G. Kanatzidis
and J. T. Hupp, Chem.–Eur. J., 2010, 16, 276.
16 K. Baooram, B. Francis, R. Bissessur and R. Narain, Compos.
Sci. Technol., 2008, 68, 617.
17 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
2008, 64, 112.
23 V. A. Blatov, Multipurpose crystallochemical analysis with
the program package TOPOS. IUCr Comp Comm Newsletter
7, 4–38, 2006; available at http://iucrcomputing.ccp14.ac.uk/
iucr top/comm-/ccom/newsletters/2006nov/.
24 (a) H. L. Jiang, T. A. Makal and H. C. Zhou, Coord. Chem.
Rev., 2013, 257, 2232; (b) G. P. Yang, L. Hou, X. J. Luan,
B. Wu and Y. Y. Wang, Chem. Soc. Rev., 2012, 41, 6992; (c)
Y. Takashima, V. M. Martínez, S. Furukawa, M. Kondo,
S. Shimomura, H. Uehara, M. Nakahama, K. Sugimoto and
S. Kitagawa, Nat. Commun., 2011, 2, 168; (d) K. L. Mulfort,
O. K. Farha, C. D. Malliakas, M. G. Kanatzidis and
J. T. Hupp, Chem.–Eur. J., 2010, 16, 276; (e) M. H. Mir,
S. Kitagawa and J. J. Vittal, Inorg. Chem., 2008, 47, 7728; (f)
B. L. Chen, S. Ma, F. Zapata, F. R. Fronczek, E. B. Lobkovsky
and H. C. Zhou, Inorg. Chem., 2007, 46, 1233.
25 (a) J. Y. Zou, H. L. Gao, W. Shi, J. Z. Cui and P. Cheng,
CrystEngComm, 2013, 15, 2682; (b) Y. J. Cui, Y. F. Yue,
G. D. Qian and B. L. Chen, Chem. Rev., 2012, 112, 1126; (c)
X. M. Jing, H. Meng, G. H. Li, Y. Yu, Q. S. Huo, M. Eddaoudi
and Y. L. Liu, Cryst. Growth Des., 2010, 10, 3489.
26 (a) P. Cui, Z. Chen, D. L. Gao, B. Zhao, W. Shi and P. Cheng,
Cryst. Growth Des., 2010, 10, 4370; (b) M. S. Wang, S. P. Guo,
Y. Li, L. Z. Cai, J. P. Zou, G. Cu, W. W. Zhou, F. K. Zheng
and G. C. Guo, J. Am. Chem. Soc., 2009, 131, 13572; (c)
L. Z. Duan, H. Wu, J. P. Ma, X. W. Wu and Y. B. Dong, Inorg.
Chem., 2010, 49, 11164.
27 (a) M. S. Wang, S. P. Guo, Y. Li, L. Z. Cai, J. P. Zou, G. Cu,
W. W. Zhou, F. K. Zheng and G. C. Guo, J. Am. Chem. Soc.,
2009, 131, 13572; (b) P. Cui, Z. Chen, D. L. Gao, B. Zhao,
W. Shi and P. Cheng, Cryst. Growth Des., 2010, 10, 4370; (c)
L. Duan, Z. H. Wu, J. P. Ma, X. W. Wu and Y. B. Dong, Inorg.
Chem., 2010, 49, 11164.
28 (a) G. Yuan, K. Z. Shao, D. Y. Du, X. L. Wang, Z. M. Su and
J. F. Ma, CrystEngComm, 2012, 14, 1865; (b) L. L. Wen,
Z. D. Lu, J. G. Lin, Z. F. Tian, H. Z. Zhu and Q. J. Meng,
Cryst. Growth Des., 2007, 7, 93; (c) S. L. Zheng, J. H. Yang,
X. L. Yu, X. M. Chen and W. T. Wong, Inorg. Chem., 2004,
43, 830.
18 A. L. Spek, Acta Crystallogr., Sect. A: Found. Crystallogr.,
1990, 46, C34.
19 S. Norbert and B. Shyam, Chem. Rev., 2012, 112, 933.
20 (a) S. R. Batten, B. F. Hoskins and R. Robson, Chem.–Eur. J.,
2000, 6, 156; (b) S. C. Manna, A. D. Jana, G. M. Rosair,
This journal is © The Royal Society of Chemistry 2014
CrystEngComm, 2014, 16, 834–841 | 841