Solvent templates induced porous metal-organic materials: Conformational isomerism and catalytic activity

Article abstract of DOI:10.1021/ic502369y

Solvent templates induced Co-based metal-organic materials; conformational isomers {[Co₂(pdpa)(CH₃CN)(H₂O)₃]·CH₃OH·H₂O}_n (1) and {[Co₂(pdpa)(CH₃CN)(H₂O)₃]}_n (2) and {[Co₅(pdpa)₂(μ₃-OH)₂(H₂O)₆]·2H₂O}_n (3) [H₄pdpa = 5,5′-(pentane-1,2-diyl)-bis(oxy)diisophthalic acid] were synthesized under the same solvothermal conditions except with different concentrations of cyclic ethers (1,4-dioxane or tetrahydrofuran) as structure-directing agents. Structural transformations from a three-dimensional (3D) framework of 1 containing channels with dimensions of μ6 ? × 6 ? to a two-dimensional layer structure of 2 consisting of large open channels with a size of μ15 ? × 8 ? and then to a 3D nonporous framework of 3, resulting from the different concentrations of cyclic ethers, were observed. The anion-π interactions between electron-efficient oxygen atoms of cyclic ethers and electron-deficient dicarboxylic acid aromatic cores in H₄pdpa imported into the synthetic process accounted for the conformational change of the ligand H₄pdpa and the following structural variations. A systematic investigation was conducted to explore how different concentrations of structure-directing agents affected the frameworks of resultant metal-organic frameworks. Furthermore, 1-3 were shown to be available heterogeneous catalysts for the synthesis of 2-imidazoline and 1,4,5,6-tetrahydropyrimidine derivatives by the cascade cycloaddition reactions of aromatic nitriles with diamines. The results showed that the catalytic activity of 2 was much higher than that of 1 and 3, because of its unique structural features, including accessible catalytic sites and suitable channel size and shape. In addition, a plausible mechanism for these catalytic reactions was proposed, and the reactivity-structure relationship was further clarified.

Full text of DOI:10.1021/ic502369y

Article
pubs.acs.org/IC
Solvent Templates Induced Porous Metal−Organic Materials:
Conformational Isomerism and Catalytic Activity
Ran Ding, Chao Huang, Jingjing Lu, Junning Wang, Chuanjun Song, Jie Wu,* Hongwei Hou,*
and Yaoting Fan
College of Chemistry and Molecular Engineering, Zhengzhou University, Henan 450052, China
*
S Supporting Information
ABSTRACT: Solvent templates induced Co-based metal−organic
materials; conformational isomers {[Co (pdpa)(CH CN)(H O) ]·
2
3
2
3
CH OH·H O} (1) and {[Co (pdpa)(CH CN)(H O) ]} (2) and
3
2
n
2
3
2
3
n
{
1
[Co (pdpa) (μ -OH) (H O) ]·2H O} (3) [H pdpa = 5,5′-(pentane-
5
2
3
2
2
6
2
n
4
,2-diyl)-bis(oxy)diisophthalic acid] were synthesized under the same
solvothermal conditions except with different concentrations of cyclic
ethers (1,4-dioxane or tetrahydrofuran) as structure-directing agents.
Structural transformations from a three-dimensional (3D) framework of
1
containing channels with dimensions of ∼6 Å × 6 Å to a two-
dimensional layer structure of 2 consisting of large open channels with a
size of ∼15 Å × 8 Å and then to a 3D nonporous framework of 3,
resulting from the different concentrations of cyclic ethers, were
observed. The anion−π interactions between electron-efficient oxygen
atoms of cyclic ethers and electron-deficient dicarboxylic acid aromatic
cores in H pdpa imported into the synthetic process accounted for the conformational change of the ligand H pdpa and the
4
4
following structural variations. A systematic investigation was conducted to explore how different concentrations of structure-
directing agents affected the frameworks of resultant metal−organic frameworks. Furthermore, 1−3 were shown to be available
heterogeneous catalysts for the synthesis of 2-imidazoline and 1,4,5,6-tetrahydropyrimidine derivatives by the cascade
cycloaddition reactions of aromatic nitriles with diamines. The results showed that the catalytic activity of 2 was much higher
than that of 1 and 3, because of its unique structural features, including accessible catalytic sites and suitable channel size and
shape. In addition, a plausible mechanism for these catalytic reactions was proposed, and the reactivity−structure relationship was
further clarified.
5
INTRODUCTION
pH value, etc. Furthermore, solvent as an external stimuli can
also affect the coordination assemblies of specific reactants from
both thermodynamic and kinetic perspectives, yielding diverse
■
The use of metal−organic frameworks (MOFs) as heteroge-
neous catalysts has attracted a growing amount of attention
because they combine the advantages of both homogeneous
and heterogeneous catalysts without their disadvantages. For
example, they are the building blocks of MOFs [i.e., metal
centers at the nodes of the constituent secondary building units
6
MOFs. The solvent templates are not only shape-selective but
also site-selective, resulting from their polarity, bulkiness, and
interactions with metal sites or organic ligands of MOFs, such
7
8
1
9
10
as a coordination bond, a hydrogen bond, an anion−π
11
12
bond, and an XH π-type bond (X = O, N, or C). It has been
determined that coordination assemblies are affected by solvent
templates in two disparate ways: (i) solvent molecules as
ligands and/or guests stay in the crystalline lattice to affect the
product structure, and (ii) solvent molecules as structure-
directing agents influence the crystal growth, framework, and
(
SBUs) and organic linkers], and the supramolecular structures
2
can be carefully tuned to adapt various catalytic reactions. The
ability to easily isolate, reuse, and recover MOF-based catalysts
is also desirable for simplifying operation and reducing the
3
levels of pollution and waste. In addition, an important
advantage of MOFs as heterogeneous catalysts is the fact that
their porous frameworks permit substrates to be transported
and to interact rapidly while possessing exceptional shape
selectivity, size selectivity, chemoselectivity, and enantioselec-
13
final morphology yet do not exist in the final structure. The
structure-directing effect of solvents is more suitable for
synthesizing heterogeneous MOF catalysts because solvent
molecules located within channels will prevent the diffusion of
reactants and products in the solid interior. Besides, removing
the solvents will leave unsaturated coordination positions of
4
tivity. These excellent features of MOF catalysts are mostly
attributed to their flexible and diverse structures. Though it is
still difficult to precisely predict the final structure of
coordination assembly, researchers have summarized many
factors that can influence the formation of MOFs, including the
metal ion, organic ligand, reaction time, temperature, pressure,
Received: September 29, 2014
©
XXXX American Chemical Society
A
DOI: 10.1021/ic502369y
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
catalytically active metal sites free to capture substrates. Though
a few examples of coordination assemblies affected by the
structure-directing effect of solvent molecules have been
reported and have become some of the most fascinating
phenomena in crystallography and materials science, the
intricate mechanism involved in these solvent-directed
coordination assemblies remains largely unclear.
pore size distributions of 2 were collected on a Micromeritics ASAP
2
420 Accelerated Surface Area and Porosimetry System under
ultrahigh vacuum in a clean system, with a diaphragm and turbo
pumping system. Ultra-high-purity-grade (>99.999%) N gas was used
2
14
in all adsorption measurements. The experimental temperature was
maintained with liquid nitrogen (77 K). Prior to measurement, the
bulk sample of 2 was washed with absolute ethanol (EtOH) three
times, dried under vacuum, and then transferred into a stainless steel
Especially, in some cases, solvent templates as structure-
directing agents do not change the SBUs or chemical
compositions of resultant MOFs but simply change the
conformation of their structural skeletons, resulting in the
formation of conformational isomers (also called as poly-
column. After 20 min of soaking and venting of supercritical CO (SC-
2
CO ) by a DB-80 simplex pump, the column pressure regulator was
2
set at 109 bar by soaking SC-CO
increased to 60 °C. SC-CO in the column was gradually vented after
and the column temperature was
2
2
1
2 h.
Synthesis of {[Co (pdpa)(CH CN)(H O) ]·CH OH·H O} (1). A
1
5
2
3
2
3
3
2
n
morphs). Conformational isomers of MOFs have attracted a
great deal of interest in the field of heterogeneous catalysis in
recent years because the isomers have identical SBUs and
organic ligands, providing a useful platform for exploring the
role of the structural features of MOFs in their shape and size
mixture of Co(NO ) ·6H O (0.058 g, 0.2 mmol), H pdpa (0.043 g,
3
2
2
4
0
.1 mmol), NaOH (0.016 g, 0.4 mmol), and a 1:2:8 CH CN/
3
CH OH/H O mixture (10 mL) was placed in a 25 mL Teflon-lined
3
2
stainless steel container. The container was sealed and heated at 160
C for 3 days. After the mixture had cooled to ambient temperature at
°
16
selectivity during catalytic reactions. In previous reports, it has
been summarized that the conformational isomers could be
obtained by altering the solvent system from polar to
a rate of 5 °C/h, purple crystals of 1 were obtained with a yield of 34%
(based on Co). Anal. Calcd for C H Co NO : C, 41.69%; H, 4.52%;
24
31
2
15
−1
N, 2.03%. Found: C, 41.58%; H, 4.69%; N, 2.17%. IR (KBr, cm ):
343 (m), 3072 (w), 2268 (s), 1616 (m), 1453 (w), 1264 (m), 1043
7
17
18
3
nonpolar, organic to inorganic, or dry to wet. However,
(
s), 773 (s), 713 (w).
Synthesis of {[Co (pdpa)(CH CN)(H O) ]} (2). A mixture of
examples of solvent-induced conformational isomers remain
1
4
2
3
2
3 n
rare.
Herein, we present a series of Co-based MOFs, conforma-
tional isomers {[Co (pdpa)(CH CN)(H O) ]·CH OH·H O}
n
Co(NO ) ·6H O (0.058 g, 0.2 mmol), H pdpa (0.043 g, 0.1 mmol),
3
2
2
4
NaOH (0.016 g, 0.4 mmol), 1,4-dioxane (or THF) (1 mL), and a
1:2:8 CH CN/CH OH/H O mixture (9 mL) was placed in a 25 mL
2
3
2
3
3
2
3
3
2
(
{
(
1) and {[Co (pdpa)(CH CN)(H O) ]} (2) and
2 3 2 3 n
Teflon-lined stainless steel container. The container was sealed and
heated at 160 °C for 3 days. After the mixture had cooled to ambient
temperature at a rate of 5 °C/h, purple crystals of 2 were obtained
[Co (pdpa) (μ -OH) (H O) ]·2H O} (3) [H pdpa = 5,5′-
5
2
3
2
2
6
2
n
4
pentane-1,2-diyl)-bis(oxy)diisophthalic acid], which were
synthesized under the same sovlothermal conditions except
with different concentrations of cyclic ethers [1,4-dioxane or
tetrahydrofuran (THF)] as structure-directing agents. With the
concentration of solvent-directing agents increasing, the
resultant structures transformed from a three-dimensional
with a yield of 79% (based on Co). Anal. Calcd for C23
H25Co NO13:
2
C, 43.08%; H, 3.93%; N, 2.18%. Found: C, 43.24%; H, 3.80%; N,
−1
2
1
.27%. IR (KBr, cm ): 3343 (m), 2946 (w), 2268 (s), 1616 (m),
454 (w), 1266 (m), 1041 (s), 774 (s), 717 (w).
Synthesis of {[Co (pdpa) (μ -OH) (H O) ]·2H O} (3). A
5
2
3
2
2
6
2
n
mixture of Co(NO ) ·6H O (0.058 g, 0.2 mmol), H pdpa (0.043 g,
3
2
2
4
(3D) porous framework of 1 to a two-dimensional (2D)
0
.1 mmol), NaOH (0.016 g, 0.4 mmol), a 1:2:8 CH CN/CH OH/
3 3
porous structure of 2 and then to a 3D nonporous 3. In
particular, 1 and 2 are solvent-induced conformational isomers.
We reasoned that the structural variations among 1−3 result
H O mixture (2 mL), and 1,4-dioxane (or THF) (8 mL) was placed in
2
a 25 mL Teflon-lined stainless steel container. The container was
sealed and heated at 160 °C for 3 days. After the mixture had cooled to
ambient temperature at a rate of 5 °C/h, purple crystals of 3 were
obtained with a yield of 65% (based on Co). Anal. Calcd for
C H Co O : C, 37.94%; H, 3.79%. Found: C, 37.84%; H, 3.68%. IR
from the conformational transformation of ligand H pdpa
4
caused by the anion−π interaction between cyclic ethers and
1
1
ligand H pdpa. In addition, we demonstrated the catalytic
42 50
5
30
4
−
1
(
KBr, cm ): 3375 (m), 3149 (m), 1662 (m), 1506 (m), 1285 (w),
potential of 1−3 with respect to the synthesis of 2-imidazoline
and 1,4,5,6-tetrahydropyrimidine derivatives by the cascade
cycloaddition reactions of diamines with aromatic nitriles. The
structure−activity relationship was clarified, indicating the
important roles of channel size and coordination environment
of metal sites in these catalytic reactions.
1
007 (m), 745 (vw).
Typical Procedure for the Synthesis of 2-Imidazoline (7a−d)
and 1,4,5,6-Tetrahydropyrimidine Derivatives (8a−d) with
Catalysts 1−3. Nitrile (1.0 mmol, 1.0 equiv, 4a−d), ethylenediamine
or 1,3-diaminopropane (0.5 mL, 5 or 6, respectively), catalyst (0.1
mmol, 0.1 equiv based on cobalt ions, 1−3), and toluene (5 mL) were
mixed and heated to reflux. After 4 h, the bulk of the cool solvent was
filtered and evaporated in vacuo, and then the residue was partitioned
EXPERIMENTAL SECTION
■
between chloroform (25 mL) and H O (25 mL). The organic phase
2
Materials and Physical Measurements. All reagents and
solvents were commercially available and used as received without
was washed with saturated aqueous NaCl, dried with Na SO , filtered,
2 4
and evaporated in vacuo. The residue was purified by column
1
further purification. H pdpa was synthesized according to a modified
chromatography on silica gel (3:1 EtOAc/MeOH). H NMR spectra
4
19
13
procedure from the literature. The atomic absorption spectrum was
recorded on a Z28000 graphite-oven atomic absorption spectropho-
tometer. Fourier transform infrared spectra were recorded on a
Bruker-ALPHA spectrophotometer with KBr pellets in the 400−4000
were recorded on a 300 MHz instrument and C NMR spectra on a
75 MHz instrument.
Crystal Data Collection and Refinement. The data of 1−3 were
collected on a Rigaku Saturn 724 CCD diffractometer (Mo Kα; λ =
0.71073 Å) at 20 ± 1 °C. Absorption corrections were applied by
using a numerical program. The data were corrected for Lorentz and
polarization effects. The structures were determined by direct methods
−1
cm region. Elemental analyses (C, H, and N) were conducted on a
FLASH EA 1112 elemental analyzer. Powder X-ray diffraction
(
PXRD) patterns were recorded using Cu Kα1 radiation on a
PANalyticalX’Pert PRO diffractometer. Thermogravimetric analyses
TGA) were performed on a Netzsch STA 449C thermal analyzer at a
2
and refined with a full-matrix least-squares technique based on F with
2
0
(
the SHELXL-97 crystallographic software package. Hydrogen atoms
were placed at calculated positions and refined as riding atoms with
isotropic displacement parameters. The SQUEEZE program imple-
mented in PLATON was used to remove electron densities in 2 and 3,
and the numbers of guest molecules for 2 and 3 were calculated by
−1
1
13
heating rate of 10 °C min in air. H and C nuclear magnetic
resonance (NMR) spectra were recorded with Bruker Avance-300
spectrometers. Liquid chromatography−mass spectrometry spectra
were measured on an Agilent MSD-1100 ESI-MS/MS system. The
B
DOI: 10.1021/ic502369y
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
TGA and elemental analysis data. Crystallographic crystal data and
structure processing parameters for 1−3 are listed in Table 1. Selected
bond lengths and bond angles for 1−3 are listed in Table S1 of the
Supporting Information.
Table 1. Crystallographic Data and Refinement Parameters
for 1−3
1
2
3
formula
fw
C H O Co
C H O Co
C H O Co5
2
4
31 15
2
23 25 13
2
42 50 30
691.36
641.30
293(2)
0.71073
triclinic
1329.47
293(2)
0.71073
orthorhombic
Fdd2
temp (K)
wavelength (Å)
crystal system
space group
a (Å)
293(2)
0.71073
monoclinic
P2 /c
1
P1
̅
7.7720(16)
18.629(4)
19.518(5)
90
10.570(2)
10.659(2)
13.810(3)
104.32(3)
103.67(3)
109.51(3)
1331.5(5)
2
23.362(5)
22.491(5)
22.738(5)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
104.23(3)
90
90
90
2739.2(11)
4
11948(4)
8
Z
D (g cm−3)
1.676
1.600
1.478
c
μ (mm−1)
1.288
1.313
1.442
F(000)
GOF on F2
1424
656
5416
1.133
0.959
0.953
no. of reflections
collected
24436
6252
5531
no. of unique
6487
6252
5531
reflections
a
R , wR [I > 2σ(I)]
0.0720, 0.1932
0.0563, 0.1505
0.0869, 0.2160
1
2
a
R = ∑||F | − |F ||/∑|F |. wR = [∑w(F − F ) /∑w(F ) ]1/2.
2
2
2
2 2
1
o
c
o
2
o
c
o
RESULTS AND DISCUSSION
■
Figure 1. (a) View of the infinite 2 spiral chain along the b axis (top)
1
Structure of {[Co (pdpa)(CH CN)(H O) ]·CH OH·H O}
and a axis (bottom). Red and green curved arrows indicate P- and M-
helicity, respectively. (b) View of the 3D framework with helical spirals
of 1. (c) View of the 3D 4,4-connected net with a topological point
2
3
2
3
3
2
n
(
1). X-ray analysis revealed that 1 is a 3D framework and
crystallizes in the monoclinic crystal system P2 /c. The
1
2
4
symbol of {4 .8 }.
asymmetric unit of 1 consists of two crystallographically
independent Co(II) ions, one completely deprotonated
pdpa4 ligand, three coordinated water molecules, and one
coordinated acetonitrile molecule (Figure S1 of the Supporting
Information). Two Co(II) centers are connected by two
−
̅
system P1. The asymmetric unit of 2 consists of two
independent Co(II) ions, one completely deprotonated
pdpa4 ligand, three coordinated water molecules, and one
coordinated acetonitrile molecule (Figure S2 of the Supporting
Information). As seen with 1, four oxygen atoms from two
carboxylate groups and two independent Co(II) ions construct
a {Co (CO ) } SBU, which is approximately identical to that of
−
4−
carboxylate groups of pdpa ligands to form a dinuclear
Co (CO ) } SBU. As shown in Figure 1a, the {Co (CO ) }
{
2
2 2
2
2 2
4−
SBUs are further extended by pdpa ligands to construct
infinite 2 helical motifs in P- and M-helicity, which should
1
2
2 2
originate from the dihedral angle between the two aromatic
1. Thus, 2 can be regarded as a conformational isomer of 1.
However, under the effect of solvent templates, the dihedral
angle between two aromatic rings of a pdpa ligand changes
rings of the pdpa4 ligand being 20.0° and the distinct
−
4
−
4−
conformations of pdpa ligand with two dicarboxylic acid
aromatic cores pointing in different directions. A significant
structural feature of 1 is that the helical spirals form open
channel dimensions of ∼6 Å × 6 Å (considering van der Waals
radii) along the a axis. The helical channels are arranged
alternatively in P- and M-helicity, leading to a 3D network with
a mesomeric lattice (Figure 1b). Topologically, 1 can be
considered as a 4,4-connected net with a topological point
from 20.0° to 0.3°, which indicates that the conformation of the
ligand transforms from distortion of 1 to planarity of 2. Thus,
4−
two {Co (CO ) } SBUs and two pdpa ligands form a closed
2
2 2
circle instead of the helical spiral of 1. All circles in the same
plane are connected by pdpa4 ligands or Co(II) SBUs, creating
a 2D framework (Figure 2a). As shown in Figure 2b, these 2D
sheets are stacked by π···π interactions with a distance of
approximately 3.7 Å, creating a 3D layer framework including
one-dimensional channels of ∼15 Å × 8 Å (Figure 2b,
considering van der Waals radii).
−
2
4
symbol of {4 .8 } (Figure 1c).
Structure of {[Co (pdpa)(CH CN)(H O) ]} (2). 2 was
2
3
2
3 n
successfully obtained under the same solvothermal conditions
that were used for 1 except with the addition of 1,4-dioxane as a
structure-directing agent (1:9 Vtemplate:Vprior solvents). X-ray
analysis indicated that 2 crystallizes in the triclinic crystal
Structure of {[Co (pdpa) (μ -OH) (H O) ]·2H O} (3). 3
5
2
3
2
2
6
2
n
was obtained under the conditions used for 2 except that the
level of 1,4-dioxane was ≥80% (by volume) of the solvent
C
DOI: 10.1021/ic502369y
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
completely different from the {Co (CO ) } SBU in 1 and 2.
2
2 2
4
−
Moreover, all carboxylate groups of symmetrical pdpa ligands
are deprotonated and adopt bismonodentate and monodentate
coordination modes to bridge pentanuclear Co(II) SBUs,
forming a 3D framework (Figure 3a). The pentanuclear Co(II)
SBU can be defined as a unimodal 8-connected node, and the
pdpa4 ligand acts as 4-connected linkers. From a topological
point of view, 3 can be considered to be a 4,8-connected net
−
3
23
2
3 3
with a topological point symbol of {4 .6 .8 }{4 .6 } (Figure
2
3
b).
Structure-Directing Effect of Solvent Templates. It has
been demonstrated that solvent molecules as structure-directing
agents can modulate the structures of MOFs, but the
achievement still remains a scarcely explored field of research,
7
especially for the synthesis of conformational isomers.
Initially, 1 was obtained as the only product by heating a
mixture of Co(NO ) ·6H O and Na pdpa in a 1:2:8 CH CN/
3
2
2
4
3
CH OH/H O mixture at 160 °C for 3 days and cooling it to
3
2
ambient temperature at 5 °C/h. Interestingly, when we treated
the reaction mixture under exactly the same conditions that are
mentioned above except with the addition of a low
concentration of 1,4-dioxane as a template (1:9
Vtemplate:Vprior solvents), 2 was obtained as the only product.
Therefore, the addition of a low concentration of 1,4-dioxane
resulted in the 3D framework of 1 changing to 2D layer
structure of 2, in which the {Co (CO ) } SBUs remained
2
2 2
4
−
invariable but the conformation of the pdpa ligand trans-
formed from slight distortion (20.0°) to planarity (0.3°). As a
result, the channel size grows from ∼6 Å × 6 Å for 1 to ∼15 Å
Figure 2. (a) View of the 2D network along the b axis. (b) Space-
filling model of the 2D stacked layer framework containing one-
dimensional channels.
×
8 Å for 2. By contrast, when the solvent volume ratio of 1,4-
dioxane to prior solvents was increased to 4:1, 3 was obtained
and exhibited a compact 3D framework with pentanuclear
cobalt [Co (μ -OH) (H O) ] SBUs, which were greatly
mixture. The result of the crystallographic analysis revealed that
5
3
2
2
2
3
exhibits a compact 3D framework and crystallizes in the
different from the SBUs of 1 and 2. The conformation of the
pdpa4 ligand returns to the distorted form (82.8°), and the
coordination environment of metal sites is dense, suppressing
the existence of available channels (Figure 4). Thus, a series of
Co-based MOFs (1−3) were successfully obtained under the
same solvothermal conditions except with different concen-
trations of 1,4-dioxane as the structure-directing agent.
The fact that the same reactions conducted at different
concentrations of 1,4-dioxane afforded entirely different
frameworks prompted us to take a systematic approach to
−
orthorhombic crystal system Fdd2. The asymmetric unit of 3
contains two and one-half Co(II) ions, one completely
deprotonated pdpa ligand, one μ -hydroxyl oxygen atom,
and three coordinated water molecules (Figure S3 of the
Supporting Information).
4−
3
Five symmetry-related Co(II) atoms (Co1, Co2, Co3, Co2A,
and Co3A) are linked together by two μ -hydroxyl oxygen
atoms and two water molecules to construct a [Co (μ -
OH) (H O) ] cluster as a pentanuclear Co(II) SBU, which is
3
5
3
2
2
2
Figure 3. (a) View of the compact 3D stacked plot of 3 along the c axis. (b) View of the 3D 4,8-connected net with a topological point symbol of
3
23
2
3 3
{
4 .6 .8 }{4 .6 } .
2
D
DOI: 10.1021/ic502369y
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 4. View of the conformational variations of the H pdpa ligand among 1−3: (a) slight distortion in 1, (b) planarity in 2, and (c) distortion in
4
3.
exploring what influence the concentration of structure-
directing agents might have upon the framework of MOFs.
The following observations are detailed in Table 2 and
supported by PXRD patterns (Figure 5). (1) Without a solvent
template, only 1 could be obtained. (2) The addition of a low
concentration of template (1:9 < Vtemplate:Vprior solvents < 1:1)
afforded 2, whereas a high concentration of solvent template
(Vtemplate:Vprior solvents > 4:1) led to 3. (3) A mixture of 2 and 3
was obtained at an intermediate concentration of solvent
template. The results indicated that the solvent volume ratio
controlled the complexes’ syntheses and a high concentration
of solvent templates tended to favor 3 over 2. We reasoned that
the prior mixture of solvents H O, CH OH, and CH CN with a
Table 2. Summary of the Products Isolated at Different
Proportions of Template Guest (1,4-dioxane or THF)
a
entry volume ratio between template and prior solvent obtained product
1
2
3
4
5
6
7
8
9
1
none
1:9
2:8
3:7
4:6
5:5
6:4
7:3
8:2
9:1
1
2
2
3
3
2
volume ratio of 8:2:1 favors the formation of dinuclear
Co (CO ) } units, which are the SBUs in both 1 and 2. 1,4-
2
{
2
2 2
2
Dioxane as structure-directing agent at low concentrations
affects only the configuration of the ligand and has no influence
on the {Co (CO ) } SBUs. In 1 and 2, two aromatic rings of
2
2 and 3
2
2 2
2 and 3
the ligand point in different directions, leading to the
conformational isomerism. By contrast, with the 1,4-dioxane:p-
rior solvent volume ratio increasing to more than half of the
mixed solvents, 3 with [Co (μ -OH) (H O) ] SBUs begins to
3
3
0
a
The prior solvent is a mixture of H O, CH OH, and CH CN with a
2
3
3
5
3
2
2
2
volume ratio of 8:2:1.
be generated, along with the formation of 2 with {Co (CO ) }
2
2 2
SBUs. When the 1,4-dioxane:prior solvent volume ratio
increases to >4:1, which favors the formation of the [Co (μ -
5
3
OH) (H O) ] units instead of the {Co (CO ) } units, 3 is
2
2
2
2
2 2
obtained as the only product.
Interestingly, THF, of which the polarity (dipole moment of
1
.75) is much larger than that of 1,4-dioxane (dipole moment
21
of 0.45), could also be used as a structure-directing agent to
obtain 2 and 3 with the same volume ratio of templates to prior
solvents as 1,4-dioxane. It indicated that the solvent structure-
directing effect herein did not result from the polarity. We
attributed this solvent effect to the anion−π interactions
between the electronegative oxygen atoms of cyclic ethers (1,4-
dioxane or THF) and electron-deficient dicarboxylic acid
aromatic cores in H pdpa because the electron-deficient π
4
systems could operate as receptors capable of binding an anion
11
or molecule with electronegative atoms. Additionally, the
addition of heterocyclic aromatic compounds (pyrrole,
pyrazine, or imidazole) containing electronegative N atoms
instead of cyclic ether (1,4-dioxane or THF) as a template at a
low concentration (0.5 equiv) under the same reaction
conditions also could achieve the structural transformation
Figure 5. PXRD patterns for 1 simulated from a CIF file (black), 2
simulated from a CIF file (dark blue), 3 simulated from a CIF file
(
green), samples in entry 1 of Table 2 (cyan), samples in entries 2−6
of Table 2 (magenta), samples in entry 7 of Table 2 (red), samples in
entry 8 of Table 2 (orange), and samples in entries 9 and 10 of Table 2
(
violet).
E
DOI: 10.1021/ic502369y
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
from 1 to 2. In comparison, adding solvents such as chloroform,
dichloromethane, cyclohexane, dimethylformamide (DMF),
morpholine, and N-methyl-2-pyrrolidone (NMP) could not
produce 1−3 successfully. The results further validated our
inference that the anion−π interactions of templates and
ligands accounted for the conformational change of ligand
Catalytic activities of 1−3 were initially evaluated in toluene at
reflux for 4 h, with aromatic nitriles (4a and 4b) and
ethanediamine as substrates. As shown in Table 3, 1 and 2
Table 3. Catalyzed Synthesis of 2-Imidazolines from 4 with
1,2-Ethanediamine
H pdpa and the following structural variations.
4
Though it has been well demonstrated that the coordination
assemblies of specific reactants will be affected by the solvents
used in reactions to influence the crystal growth, crystalline
morphology, and lattice structure of the final solid, studies that
aimed to determine if the ratio of template to a mixed solvent is
a controlling factor in determining the ultimate topologies of a
22
series of MOFs are really rare. Besides, we proved that the
templates in this work as structure-directing agents at low
concentrations could influence the configuration of the ligand
rather than the SBUs, thus providing an effective means of
leading to conformational isomerism. This methodology is
different from that described for the previously reported
conformational isomers obtained by altering the solvent system
from polar to nonpolar, organic to inorganic, or dry to wet and
can easily achieve the conformational isomerism in a more
controlled way. More importantly, we reasoned that conforma-
tional isomers 1 and 2 could be directly attributed to the
anion−π interaction between electron-efficient atoms of
templates and electron-deficient dicarboxylic acid aromatic
cores in H pdpa introduced into the process of self-assembly.
4
TGA of 1−3. The TGA experiments were conducted to
investigate the thermal stability of 1−3 (Figure S4 of the
Supporting Information). The result for 1 shows a weight loss
of 7.5% (calcd, 7.2%) in the range of 50−120 °C attributed to
the departure of one water molecule and one methanol
molecule, and 1 begins to lose its four coordinated solvent
molecules at 150 °C, of which the weight is 13.4% (calcd,
1
3.7%). The main skeleton of 1 begins to collapse at 330 °C.
The curve of 2 reveals that a preliminary weight loss of 13.9%
(
calcd, 14.8%) ranging from 100 to 150 °C is attributed to the
removal of three water molecules and one acetonitrile molecule.
After that, the decomposition of H pdpa ligands occurs at 330
4
°
C. As for 3, the weight loss of 10.0% (calcd, 10.8%) in the
range of 50−200 °C is due to the departure of six lattice water
molecules and two uncoordinated water molecules, and the
ligands of 3 collapse at 310 °C.
Catalytic Capacity of 1−3. As useful building blocks in
biochemistry and pharmacology, 2-substituted 1,4,5,6-tetrahy-
dropyrimidine and 2-imidazoline derivatives attracted a great
deal of interest for their potential anthelmintic, antidepressant,
23
antibacterial, and fungicide activity. In particular, many
researchers have focused on the catalytic cascade cycloaddition
reaction of aromatic nitriles with diamines because it is a direct
method for synthesizing imidazoline and tetrahydropyrimidine
24
rings according with the requirements of green chemistry.
However, the design and synthesis of effective heterogeneous
MOF catalysts for this reaction and the relationship between
the structural features of MOFs and their catalytic activities still
need to be studied further.
The excellent match between the experimental and simulated
PXRD patterns of 1−3 proved the phase purity of their bulky
crystalline samples (Figure S5 of the Supporting Information).
To study the potentials of 1−3 as heterogeneous catalysts in
the catalytic cascade cycloaddition reaction of aromatic nitriles
with diamines, we compared their activities with homogeneous
Co(OAc)2 by keeping the Co content the same (10%).
were effective catalysts for the cascade cyclization of aromatic
nitriles (4a and 4b) with 1,2-ethanediamine, leading to 7a and
7b, respectively, with moderate to high yields (45−89%). In
comparison, Co(OAc)2 as a homogeneous catalyst gave
cycloaddition products 7a and 7b with yields of 59 and 35%,
respectively. Importantly, the catalytic activity of 2 was higher
than that of 1, giving yields of 89 and 60% for 7a and 7b,
respectively. By contrast, 3 provided poor yields for 7a and 7b,
indicating its catalytic capacity is lower than those of 1 and 2.
Similarly, with respect to the synthesis of 2-substituted 1,4,5,6-
tetrahydropyrimidines by the cascade cycloaddition reactions of
F
DOI: 10.1021/ic502369y
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
aromatic nitriles (4a and 4b) with 1,3-propanediamine, 1 gave a
moderate yield, 2 was highly effective and could generate the
desired products 8a and 8b in yields of 89 and 81%,
respectively, while 3 gave poor conversions (Table 4).
Co(OAc) as the catalyst under the same reaction conditions.
2
Substrates 4a−4d when subjected to catalysis by Co(OAc) did
2
not follow the order of decrease of 1 and 2. Therefore, the
substrate size should be an important factor for determining the
yield of the heterogeneous catalytic reaction.
According to the structural analysis of 1−3, they exhibit
Table 4. Catalyzed Synthesis of 1,4,5,6-
Tetrahydropyrimidines from 4 with 1,3-Propanediamine
various channel dimensions from ∼6 Å × 6 Å for 1 to ∼15 Å ×
8
Å for 2 to nonporosity for 3. The catalytic capacity of 1−3
increases in the order 2 > 1 > 3, consistent with the expansion
of their channel sizes. This trend indicates that the channel
features could be a crucial factor in determining the reaction
rate for the MOF-catalyzed cascade cycloaddition of aromatic
nitriles with diamines. The pore size distributions (PSDs) of 2
after SC-CO activation exhibit a main pore size distribution
2
centered around 15 Å (Figure S6 of the Supporting
Information). The large channels of 2 could facilitate the
transport of organic substrates and products and provide
enough space where substrates could access and react with
25
catalytic active sites. In addition, 1 and 2 are conformational
isomers and contain the same SBUs and organic ligands but
differ in the conformations of their skeletons. Conformational
isomers 1 and 2 could provide an excellent platform for
exploring the effect of channel size and structural features on
heterogeneous catalysis because they eliminated the interfer-
ence afforded by the variations of metal sites and organic
ligands. As shown in entries 2 and 3 of Tables 3 and 4, both 1
and 2 are effective and give similar yields with substrate 4a.
However, with the size of the substrate increasing, the catalytic
activity of 1 decreased apparently and was lower than that of 2.
For the bulky substrate 4d with dimensions of 6.73 Å × 6.46 Å,
1
7
was completely inactive but 2 gave a conversion of 15% for
d (6.61 Å × 7.76 Å) and 12% for 8d (6.64 Å × 8.16 Å).
Because 1 and 2 have the same SBUs and elementary
composition, this difference should be ascribed to the channel
size of 1 not matching with bulky 4d. As a result, 2 gave a
catalytic activity higher than that of 1, proving the importance
of channel sizes to the MOF catalysts.
To further confirm that the catalytic reactions proceeded
within the crystal voids, large crystals of 2 (∼0.3 mm × 0.25
mm × 0.2 mm) without grinding and stirring were used as the
catalyst for the synthesis of 8a, giving a yield of 50% under the
same reaction conditions. Because large crystals have too few
surface catalytic sites to meet the requirement of the reaction,
interior channels proved to be the place within which the
reaction proceeds. Additionally, atomic absorption analysis of
the filtrate showed a low level of remaining cobalt ions (<1
ppm), strongly confirming its heterogeneity.
Scheme 1. Proposed Mechanism for the Synthesis of 2-
Imidazolines Catalyzed by Co-Based MOFs
To prove the effect of the substrate size in this reaction, we
conducted the processes catalyzed by 1−3 with the more bulky
substrates 4c and 4d as substrates (entries 9−16 in Tables 3
and 4). With an increase in the bulk of aromatic nitriles, the
yields of reactions catalyzed by 1 and 2 obviously decreased in
the order 4a > 4b > 4c > 4d, corresponding to the increase in
substrate size. With the more bulky 4d, only a trace amount of
the desired compound was produced when 2 was used as a
heterogeneous catalyst, while 1 and 3 were unsuitable catalysts.
To eliminate the possibility of the different reactivity of 4a−4d
generating such a decrease, experiments were conducted with
G
DOI: 10.1021/ic502369y
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 6. Comparison of the PXRD patterns of 2 before and after catalysis.
The mechanism for the synthesis of 2-imidazolines catalyzed
by 2 has been proposed tentatively (Scheme 1). The nitrile is
first activated by the catalyst to give I. Ethanediamine attacks I
to afford II. Cyclization of II gives the final product. In
addition, we reasoned that the coordination environment of
metal sites in 1 and 2 also plays an important role in
determining their catalytic activities. The cobalt ions in
conformational isomers 1 and 2 are coordinated with not
only carboxylic groups but also water molecules. Because water
molecules are good leaving groups, they may facilitate
departure during the catalytic process, leaving unsaturated
cobalt sites exposed to aromatic nitriles.
2-substituted 1,4,5,6-tetrahydropyrimidines, indicating that the
channel size has a positive effect on the catalytic ability of
heterogeneous catalysts.
ASSOCIATED CONTENT
Supporting Information
■
*
S
X-ray crystallographic information for 1−3 in CIF format,
coordination environment of 1−3, TGA plots and PXRD
1
patterns for 1−3, selected bond lengths and angles for 1−3, H
13
NMR and C NMR data for 7a−7d and 8a−8d, results of the
reusability experiment, and pore size distributions of 2. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Compared with previously reported catalysts for this kind of
2
6
27
28
29
reaction, such as La(OTf) , CuCl, sulfur, CS2, and
2
3
3
0
H S, 2 as a heterogeneous catalyst has several advantages,
AUTHOR INFORMATION
Corresponding Authors
E-mail: wujie@zzu.edu.cn.
E-mail: houhongw@zzu.edu.cn. Fax: (86)371-67761744.
■
such as a higher catalytic activity stemming from its capability in
stabilizing the intermediates, boosted catalyst stability arising
from the spatial separation of single catalytic sites, reusability,
steric hindrance selectivity, and environmental friendliness. 2
recovered from the catalytic reaction via centrifugation and
filtration could be recycled and reused at least four times
*
*
Notes
The authors declare no competing financial interest.
(
Figure S7 of the Supporting Information). Moreover, the
ACKNOWLEDGMENTS
■
PXRD of 2 recovered from the reaction closely matched that of
the pristine solid of 2, strongly proving that 2 is stable under
the catalytic condition (Figure 6).
This work was funded by the National Natural Science
Foundation of China (21201152 and 21371155) and the
Research Fund for the Doctoral Program of Higher Education
of China (20124101110002).
CONCLUSION
■
REFERENCES
In summary, with cyclic ethers (THF or 1,4-dioxane) as
structure-directing agents, the assemblies of cobalt nitrate and
■
(1) (a) Hasegawa, S.; Horike, S.; Matsuda, R.; Furukawa, S.;
Mochizuki, K.; Kinoshita, Y.; Kitagawa, S. J. Am. Chem. Soc. 2007, 129,
ligand H pdpa under the same solvothermal condition resulted
4
2
8
2
607−2614. (b) Tanaka, K.; Oda, S.; Shiro, M. Chem. Commun. 2008,
20−822. (c) Evans, O. R.; Ngo, H. L.; Lin, W. J. Am. Chem. Soc.
001, 123, 10395−10396. (d) Henschel, A.; Gedrich, K.; Kraehnert,
R.; Kaskel, S. Chem. Commun. 2008, 4192−4194. (e) Horike, S.;
Dinca, M.; Tamaki, K.; Long, J. R. J. Am. Chem. Soc. 2008, 130, 5854−
855. (f) Liu, J. W.; Chen, L. F.; Cui, H.; Zhang, J. Y.; Zhang, L.; Su,
in three solvent-induced Co-based MOFs 1−3 with different
structural features. Furthermore, systematically tuning the
frameworks and the cavity shapes of MOFs 1−3 could be
accomplished by simply changing the concentration of
introduced solvent templates. The interactions between the
oxygen atoms of the template guest (1,4-dioxane or THF) and
electron-deficient dicarboxylic acid aromatic cores in H pdpa,
the so-called anion−π interactions, could influence the
configuration of ligand H pdpa and the following structural
variations. In particular, in the case without solvent templates or
with a low concentration of solvent templates, porous
conformational isomers 1 and 2 with identical SBUs and
organic ligands, but consisting of different structural skeletons
and channels, were obtained. Thus, herein we provide a method
for obtaining conformational isomers in a more controlled way.
Further catalytic experiments showed that 2 was an effective
heterogeneous catalyst for the synthesis of 2-imidazolines and
5
C. Y. Chem. Soc. Rev. 2014, 43, 6011−6061. (g) Dhakshinamoorthy,
A.; Garcia, H. Chem. Soc. Rev. 2014, 43, 5750−5765.
4
́
(2) (a) Corma, A.; Garcia, H.; Llabres i Xamena, F. X. Chem. Rev.
2
010, 110, 4606−4655. (b) Tanski, J. M.; Wolczanski, P. T. Inorg.
4
Chem. 2001, 40, 2026−2033. (c) Zhang, X.; Llabres i Xamena, F. X.;
́
Corma, A. J. Catal. 2009, 265, 155−160. (d) Suslick, K. S.; Bhyrappa,
P.; Chou, J. H.; Kosal, M. E.; Nakagaki, S.; Smithenry, D. W.; Wilson,
S. R. Acc. Chem. Res. 2005, 38, 283−291. (e) Seo, J. S.; Whang, D.;
Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim, K. Nature 2000, 404, 982−
9
(
86.
3) (a) Corkum, E. G.; Hass, M. J.; Sullivan, A. D.; Bergens, S. H.
Org. Lett. 2011, 13, 3522−3525. (b) Amarajothi, D.; Mercedes, A.;
Hermenegildo, G. ACS Catal. 2011, 1, 48−53. (c) Anh, P.; Alexander,
H
DOI: 10.1021/ic502369y
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
U. C.; Felipe, G.; Carolyn, B. K.; Omar, M. Y. Inorg. Chem. 2011, 50,
(19) Shao, X. B.; Jiang, X. K.; Wang, X. Z.; Li, Z. T.; Zhu, S. Z.
Tetrahedron 2003, 59, 4881−4889.
7
3
(
388−7390. (d) Kesanli, B.; Lin, W. B. Coord. Chem. Rev. 2003, 246,
05−326.
(20) (a) Sheldrick, G. M. SHELXS 97, Program for the solution of
4) (a) Wang, C.; Zheng, M.; Lin, W. B. J. Phys. Chem. Lett. 2011, 2,
Crystal Structures; University of Go
(b) Sheldrick, G. M. SHELXS 97, Program for the Refinement of Crystal
Structures; University of Gottingen: Gottingen, Germany, 1997.
̈ ̈
ttingen: Gottingen, Germany, 1997.
1
701−1709. (b) Ma, L.; Falkowski, J. M.; Abney, C.; Lin, W. Nat.
Chem. 2010, 2, 838−846. (c) Kortunov, P. V.; Heinke, L.; Arnold, M.;
Nedellec, Y.; Jones, D. J.; Caro, J.; Karger, J. J. Am. Chem. Soc. 2007,
̈
̈
(21) Loudon, G. M. Organic Chemistry, 4th ed.; Oxford University
Press: New York, 2002.
1
29, 8041−8047. (d) Oxford, G. A. E.; Snurr, R. Q.; Broadbelt, L. J.
Ind. Eng. Chem. Res. 2010, 49, 10965−10973. (e) Oxford, G. A. E.;
Dubbeldam, D.; Broadbelt, L. J.; Snurr, R. Q. JJ. Mol. Catal. A: Chem.
(22) Fu, A. Y.; Jiang, Y. L.; Wang, Y. Y.; Gao, X. N.; Yang, G. P.; Hou,
L.; Shi, Q. Z. Inorg. Chem. 2010, 49, 5495−5502.
2
011, 334, 89−97. (f) Falkowski, J. M.; Wang, C.; Liu, S.; Lin, W. B.
(23) (a) Dunbar, P. G.; Durant, G. J.; Fang, Z.; Abuh, Y. F.; El-
Assadi, A. A.; Ngur, D. O.; Periyasamy, S.; Hoss, W. P.; Messer, W. S.
J. Med. Chem. 1993, 36, 842−847. (b) Dolinkin, A. O.; Chernov’yants,
M. S. Pharm. Chem. J. 2010, 44, 99−106.
Angew. Chem., Int. Ed. 2011, 50, 8674−8678. (g) Huang, C.; Ding, R.;
Song, C. J.; Lu, J. J.; Liu, L.; Han, X.; Wu, J.; Hou, H. W.; Fan, Y. T.
Chem.Eur. J. 2014, 20, 16156−16163.
(
5) (a) Sakamoto, H.; Matsuda, R.; Bureekaew, S.; Tanaka, D.;
(24) An, S. J.; Yin, B.; Liu, P.; Li, X. G.; Li, C.; Li, J. L.; Shi, Z.
Synthesis 2013, 45, 2525−2532.
Kitagawa, S. Chem.Eur. J. 2009, 15, 4985−4989. (b) Li, C. P.; Zhao,
(25) Song, F. J.; Wang, C.; Falkowski, J. M.; Ma, L. Q.; Lin, W. B. J.
X. H.; Chen, X. D.; Yu, Q.; Du, M. Cryst. Growth Des. 2010, 10, 5034−
Am. Chem. Soc. 2010, 132, 15390−15398.
5
1
042. (c) Li, C. P.; Yu, Q.; Chen, J.; Du, M. Cryst. Growth Des. 2010,
0, 2650−2660. (d) Yu, Q.; Zhang, X. Q.; Bian, H. D.; Liang, H.;
(26) Forsberg, J. H.; Spaziano, V. T.; Balasubramanian, T. M.; Liu, G.
K.; Kinsley, S. A.; Duckworth, C. A.; Poteruca, J. J.; Brown, P. S.;
Zhao, B.; Yan, S. P.; Liao, D. Z. Cryst. Growth Des. 2008, 8, 1140−
1
7
(
Miller, J. L. J. Org. Chem. 1987, 52, 1017−1021.
146. (e) Cook, T. R.; Zheng, Y. R.; Stang, P. J. Chem. Rev. 2013, 113,
34−777.
6) (a) Chen, S. C.; Zhang, Z. H.; Huang, K. L.; Chen, Q.; He, M. Y.;
(27) Rousselet, G.; Capdevielle, P.; Maumy, M. Tetrahedron Lett.
1
(
993, 34, 6395−6398.
28) Mirkhani, V.; Moghadam, M.; Tangestaninejad, S.; Kargar, H.
Teterahedron Lett. 2006, 47, 2129−2132.
29) Corbel, J. C.; Uriac, P.; Huet, J.; Martin, C. A. E.; Advenier, C.
Eur. J. Med. Chem. 1995, 30, 3−13.
30) Levesque, G.; Gressier, J.-C.; Proust, M. Synthesis 1981, 963−
65.
Cui, A. J.; Li, C.; Liu, Q.; Du, M. Cryst. Growth Des. 2008, 8, 3437−
445. (b) Norbert, S.; Shyam, B. Chem. Rev. 2012, 112, 933−969.
7) Huang, X. C.; Zhang, J. P.; Lin, Y. Y.; Chen, X. M. Chem.
Commun. 2005, 2232−2234.
8) (a) Ma, L. Q.; Lin, W. B. J. Am. Chem. Soc. 2008, 130, 13834−
3835. (b) Tynan, E.; Jensen, P.; Kruger, P. E.; Lees, A. C. Chem.
3
(
(
(
9
(
1
Commun. 2004, 776−777. (c) Schareina, T.; Schick, C.; Kempe, R. Z.
Anorg. Allg. Chem. 2001, 627, 131−133.
(
9) (a) Tzeng, B. C.; Yeh, H. T.; Chang, T. Y.; Lee, G. H. Cryst.
Growth Des. 2009, 9, 2552−2555. (b) Senkovska, I.; Kaskel, S. Eur. J.
Inorg. Chem. 2006, 4564−4569. (c) Dinca, M.; Long, J. R. J. Am. Chem.
Soc. 2005, 127, 9376−9377.
(
10) (a) Lin, J. B.; Zhang, J. B.; Zhang, W. X.; Xue, W.; Xue, D. X.;
Chen, X. M. Inorg. Chem. 2009, 48, 6652−6660. (b) Burrows, A. D.;
Cassar, K.; Friend, R. M. W.; Mahon, M. F.; Rigby, S. P.; Warren, J. E.
CrystEngComm 2005, 7, 548−550. (c) Li, C. P.; Du, M. Chem.
Commun. 2011, 47, 5958−5972.
(
11) (a) Tanaka, D.; Masaoka, S.; Horike, S.; Furukawa, S.; Mizuno,
M.; Endo, K.; Kitagawa, S. Angew. Chem., Int. Ed. 2006, 45, 4628−
4
8
(
631. (b) Wang, D. X.; Wang, M. X. J. Am. Chem. Soc. 2013, 135,
92−897.
12) Kasai, K.; Fujita, M. Chem.Eur. J. 2007, 13, 3089−3105.
(
13) (a) Li, C. P.; Tian, Y. L.; Guo, Y. M. Inorg. Chem. Commun.
2
008, 11, 1405−1408. (b) He, M. Y.; Chen, S. C.; Zhang, Z. H.;
Huang, K. L.; Yin, F. H.; Chen, Q. Inorg. Chim. Acta 2009, 362, 2569−
576. (c) Fromm, K. M.; Doimeadios, J. L. S.; Robin, A. Y. Chem.
2
Commun. 2005, 4548−4550.
(
(
14) Li, C. P.; Du, M. Chem. Commun. 2011, 47, 5958−5972.
15) (a) Hennigar, T. L.; MacQuarrie, D. C.; Losier, P.; Rogers, R.
D.; Zaworotko, M. J. Angew. Chem., Int. Ed. 2003, 36, 972−973.
(
b) Zhang, K. P.; Huang, X. C.; Chen, X. M. Chem. Soc. Rev. 2009, 38,
2
385−2396. (c) Makal, T. A.; Yakovenko, A. A.; Zhou, H. J. Phys.
Chem. Lett. 2011, 2, 1682−1689. (d) Du, M.; Li, C. P.; Chen, M.; Ge,
Z. W.; Wang, X.; Wang, L.; Liu, C. S. J. Am. Chem. Soc. 2014, 136,
1
0906−10909. (e) Chen, X. D.; Zhao, X. H.; Chen, M.; Du, M.
Chem.Eur. J. 2009, 15, 12974−12977.
16) (a) Kishan, M. R.; Tian, J.; Thallapally, P. K.; Fernandez, C. A.;
(
Dalgarno, S. J.; Warren, J. E.; McGrail, B. P.; Atwood, J. L. Chem.
Commun. 2010, 46, 538−540. (b) Zhu, N. Y.; Lennox, M. J.; Duren,
T.; Schmiit, W. Chem. Commun. 2014, 50, 4207−4210.
(
17) (a) Chen, X. D.; Du, M.; Mak, T. C. W. Chem. Commun. 2005,
417−4419. (b) Braga, D.; Maini, L.; Mazzeo, P. P.; Ventura, B.
Chem.Eur. J. 2010, 16, 1553−1559.
18) (a) Chen, C. Y.; Cheng, P. Y.; Wu, H. H.; Lee, H. M. Inorg.
Chem. 2007, 46, 5691−5699. (b) Frahm, D.; Hoffmann, F.; Froba, M.
Cryst. Growth Des. 2014, 14, 1719−1725.
4
(
̈
I
DOI: 10.1021/ic502369y
Inorg. Chem. XXXX, XXX, XXX−XXX