Tuning the Ionicity of Stable Metal-Organic Frameworks through Ionic Linker Installation

Article abstract of DOI:10.1021/jacs.8b12530

The predictable topologies and designable structures of metal-organic frameworks (MOFs) are the most important advantages for this emerging crystalline material compared to traditional porous materials. However, pore-environment engineering in MOF materia

Full text of DOI:10.1021/jacs.8b12530

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Article
Tuning the Ionicity of Stable Metal-Organic
Frameworks through Ionic Linker Installation
Jiandong Pang, Shuai Yuan, Jun-Sheng Qin, Christina Lollar, Ning Huang, Jialuo
Li, Qi Wang, Mingyan Wu, Daqiang Yuan, Maochun Hong, and Hong-Cai Zhou
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b12530 • Publication Date (Web): 28 Jan 2019
Downloaded from http://pubs.acs.org on January 28, 2019
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Tuning the Ionicity of Stable Metal-Organic Frameworks
through Ionic Linker Installation
Jiandong Pang,†,# Shuai Yuan,†,# Jun-Sheng Qin,† Christina T. Lollar,† Ning Huang,† Jialuo Li,† Qi
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Wang,† Mingyan Wu,‡,§ Daqiang Yuan,*,‡,§ Maochun Hong,‡,§ and Hong-Cai Zhou*,†
†Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, United States
‡State Key Laboratory of Structure Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of
Sciences, Fuzhou, Fujian 350002, China
§University of Chinese Academy of Sciences, Beijing 100049, China
Supporting Information Placeholder
ABSTRACT: The predictable topologies and designable structures of metal-organic frameworks (MOFs) are the most important
advantages for this emerging crystalline material compared to traditional porous materials. However, pore-environment engineering
in MOF materials is still a huge challenge when it comes to the growing requirements of expanded applications. A useful method
for the regulation of pore-environments, linker installation, has been developed and applied to a series of microporous MOFs.
Herein, employing PCN-700 and PCN-608 as platforms, ionic linker installation was successfully implemented in both
microporous and mesoporous Zr-based MOFs to afford a series of ionic frameworks. Selective ionic dye capture results support the
ionic nature of these MOFs. The mesopores in PCN-608 are able to survive after installation of the ionic linkers, which is useful for
ion exchange and further catalysis. To illustrate this, Ru(bpy)32+, a commonly used photoactive cation, was encapsulated into the
anionic mesoporous PCN-608-SBDC via ion exchange. Photocatalytic activity of Ru(bpy)3@PCN-608-SBDC was examined by
aza-Henry reactions, which show good catalytic performance over three catalytic cycles.
iconicity of the whole framework. A representative example is
INTRODUCTION
IRMOF-76, a cationic MOF possessing imidazolium moieties
(NHC precursors) on each linker.28
Metal–organic frameworks (MOFs), also known as porous
coordination polymers (PCPs), have attracted considerable
research attention owing to their unlimited structural diversity
and functional tunability.1-4 Indeed, the pore environment of
MOFs can be precisely designed with atomic precision,
leading to numerous advances in basic sciences and
applications including gas storage, separation, ion exchange,
chemical sensing, catalysis, energy harvesting, and
biomedicine.5-17 MOF structures are formed by connecting
metal-containing nodes with organic linkers through
coordination bonds. The positive charges of the metal cations
are usually compensated by the negatively charged organic
linkers forming an electrically neutral framework.18 By virtue
of the high tunability of framework fragments, ionic MOFs
may be realized through residual charges on the framework
and counterions in the cavity. Ionic MOFs represent a unique
class of MOF materials that combines inherent porosity,
structural tunability, and ion exchange capability. They have
been explored as potential alternatives to conventional ion
exchangers for various applications including ion separation,
water purification, etc.19-24
Compared with the myriad of neutral MOFs in the literature,
the field of ionic MOFs is less explored possibly due to
synthetic difficulties.29 Indeed, there have been a limited
number of charged metal clusters that are suitable for MOF
synthesis. Employment of organic linkers with extra charge
may often lead to unexpected framework structures during
self-assembly. In addition, some charged functional groups,
+
such as -NR3 , cannot survive harsh solvothermal synthesis
conditions. Moreover, counterion exchange might occur,
whereby free Na+ is replaced with strongly coordinating
transition metals, thus deactivating the -SO3 Na+ groups.
-
Amongst the scarce number of ionic MOFs, many of them
exhibit limited chemical stability. This hinders the practicality
of ionic MOFs because acidic or basic conditions are usually
required for material regeneration after ion exchange.
Compared with the well-established synthetic methods for
neutral MOFs, a general method to simultaneously control the
structure, stability, and ionicity of MOFs is still lacking. This
synthetic difficulty is attributed to an inherent lack of MOF
formation control in one-pot reactions.
To construct ionic MOFs, one of two main strategies are
adopted. First, ionic MOFs can be constructed from utilization
of charged metal clusters as inorganic building units. For
example, Feng and coworkers have constructed a series of
Recently, our group developed a stepwise synthetic method,
namely linker installation, to introduce functional groups into
stable MOFs under mild conditions.30 In this method, Zr-
MOFs with coordinatively unsaturated Zr6O4(OH)8(H2O)4
clusters are selected as matrices. Linear dicarboxylate linkers
with specific functional groups are subsequently installed into
the matrices by occupying the coordination vacancies on the
+
cationic MOFs based on positively charged In3O(COO)6
clusters.25-27 Secondly, extra charges can be introduced onto
-
+
the organic linkers by -SO3 or -NR3 groups, which alter the
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Zr6O4(OH)8(H2O)4 clusters.31-33 Herein, we propose that
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PCN-222 and NU-1000, can also be obtained utilizing C2v
symmetry, tetratopic carboxylate ligands which are also based
on coordinatively unsaturated 8-connected Zr6 clusters.
Furthermore, a similar open pocket can be observed in PCN-
608 with a size of approximately 8.2 Å, which is expected to
fit a BDC ligand (Figure S7). Therefore, PCN-608 was
selected as the mesoporous prototype MOF for installation of
the ionic linkers.
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linkers with designated ionic functional groups can be
installed into stable Zr-MOFs to tune the ionicity of the whole
structure without altering the pore size or stability. Using this
method, cationic and anionic moieties were incorporated into a
series of microporous and mesoporous MOFs. The resulting
cationic and anionic Zr-MOFs represents a combination of
high chemical stability, tunable porosity, and adjustable
ionicity.
Tuning the Ionicity of MOFs by Linker Installation.
Constructed by the linear Me2-BPDC ligand (2,2'-dimethyl-
biphenyl-4,4’-dicarboxylic acid) and Zr6 cluster, PCN-700 can
be considered a structural derivative of the famous UiO-67
with four linkers in the equatorial plane of the octahedral
secondary building unit eliminated (Figure 1a & 1e).
Therefore, the topology of PCN-700 was changed to a 8-c bcu
network from that of a 12-c fcu framework with a decrease in
the connection number of the Zr6 cluster. As has been
confirmed in our previous work, an H2BDC (1,4-
benzenedicarboxylic acid) ligand can be post-synthetically
installed into PCN-700 and connected to two neighboring Zr6
clusters along the c-axis (Figure 1c & 1g). Accordingly, two
geometrically equivalent linear dicarboxylate ligands, i.e.
9
RESULTS AND DISCUSSION
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Selection of the MOF Platforms. Our group has previously
confirmed PCN-700 as a good microporous MOF candidate
for linker installation.31 Besides the coordinatively-unsaturated
Zr6 clusters, the inherent flexibility of PCN-700 also plays an
important role in the process of linker installation. Therefore, a
mesoporous Zr-MOF with both 8-connected Zr6 clusters and
intrinsic flexibility makes for a perfect platform to apply this
strategy. In addition to PCN-700, we have also constructed a
series of similar microporous Zr-MOFs based on tetratopic
carboxylate ligands, i.e. the PCN-605, PCN-606, and PCN-
609 series, which also show significant flexibility due to the
rotation and deformation of the ligands.33-35 Multi-step linker
installation has been especially successful in the scu topology
PCN-606 and PCN-609 series to afford several quaternary or
quinary multivariate MOFs. Luckily, the PCN-608 series, a
class of mesoporous MOFs that are topologically similar to
H2MPDC
(2,5-dicarboxy-1-methylpyridin-1-ium)
and
H3SBDC (2-sulfoterephthalic acid), were selected to install
into PCN-700 to form positively and negatively charged
microporous MOFs.
As-synthesized single crystals of PCN-700 were
Figure 1. Structures of (a) PCN-700, (b) PCN-700-MPDC, and (c) PCN-700-BDC viewed along the a-axes. (d) Structure of PCN-700-
SBDC viewed along the b-axis. The square 1D channels in (e) PCN-700, (f) PCN-700-MPDC, (g) PCN-700-BDC, and (h) PCN-700-
SBDC viewed along the c-axes. The MPDC- ligand in PCN-700-MPDC and the SBDC3- ligand in PCN-700-SBDC show significant
disorder. Only one installed linker is shown in (b) and (d) for clarity. Color scheme: black, C; red, O; dark blue, N; yellow, S; light blue,
Zr; pink, I; khaki, Na.
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Figure 2. Structure of (a) PCN-608, (b) PCN-608-MPDC, (c) PCN-608-BDC, and PCN-608-SBDC viewed along the (1, 2, 0) direction.
The hexagonal 1D channels in (e) PCN-608, (f) PCN-608-MPDC, (g) PCN-608-BDC, and (h) PCN-608-SBDC viewed along the c-axes.
The MPDC- ligand in PCN-608-MPDC and the SBDC3- ligand in PCN-608-SBDC show significant disorder. Only one installed linker is
shown in (b) and (d) for clarity. Color scheme: black, C; red, O; dark blue, N; yellow, S; light blue, Zr; pink, I; khaki, Na; light orange,
substituents
on
the
ligands
including
-NH2
or
-OMe
groups.
o
immersed in DMF solutions of MPDC or SBDC at 85 C
overnight to give the anionic or cationic MOFs, PCN-700-
MPDC or PCN-700-SBDC, respectively. Single crystal X-ray
diffraction experiments show that all the ionic MOFs remain
in the tetragonal space group P42/mmc with the c- axes slightly
decreased after linker installation. The structure of the ionic
PCN-700 is similar to that of PCN-700-BDC and the
topologies of the MOF changed from a 8-c bcu to a 10-c bct
network (Figure S9). The methyl group on MPDC and the
sulfonic acid group on SBDC are highly disordered because of
the high symmetry of the frameworks. As shown in Figure 1,
the counterions are located in the square 1D channels along
the c-axes. Powder X-ray diffraction (PXRD) were measured
to check the phase purity of the ionic MOFs (Figure S10). The
linker ratios in the ionic PCN-700 derivatives were determined
by 1H NMR measurements of the digested samples (Figure S1
and S2, Table S1). The experimental results are a little higher
than those calculated from single crystal data because some of
the linear linkers may coordinate to the Zr6 cluster with only
one carboxylate, leaving the other end dangling.
that the a- and c-axes of PCN-608-NH2-BDC (40.97 Å and
14.81 Å, respectively) are slightly different from that of PCN-
608-NH2 (41.05 Å and 14.69 Å, respectively) with the space
group remaining unchanged. Careful analysis of the single
crystal structure of PCN-608-NH2-BDC indicate that the
BDC2- ligand installed into PCN-608-NH2 is also connected to
two neighboring Zr6 clusters along the c-axis, as expected
(Figure 2c and 2g). After linker installation, the Zr6 cluster in
the mesoporous MOF becomes a 10-connected node and the
framework PCN-608-NH2-BDC adopts
a
rare {4,10}-c
symbol of
network with topological point
a
{32.42.52}2{38.416.58.613} (Figure S9).36 It should be noted that
10-connected Zr6 cluster or 12-connected Zr6 cluster should be
exist in the as-synthesized PCN-608-NH2 or PCN-608-NH2-
BDC if we considered the terminal coordinated
monocarboxylate (such as benzoate and trifluoroacetate) or
BDC ligand as one ‘connection’. However, this mono-
coordination mode is not stable, and tends to be removed by
solvent washing and activation. Therefore, the Zr6 clusters are
considered as 8-connected nodes in PCN-608-NH2 and as 10-
connected nodes in PCN-608-NH2-BDC.
As has been reported previously, the PCN-608 series of
MOFs crystallize in the hexagonal space group P6/mmm with
3.3 nm hexagonal 1D open channels along the c-axis (Figure
2a and 2e). Each Zr6 cluster in PCN-608 connects to eight
fully deprotonated TPCB4- fragments and, conversely, each
TPCB4- fragment links to four Zr6 clusters (Figure S8).
Briefly, PCN-608 adopts the {4,8}-c csq network if we
simplify the ligands as planar 4-connected nodes and the Zr6
clusters as 8-connected nodes (Figure S9). Firstly, the amino-
substituted PCN-608 was chosen due to the high quality of its
single crystals. As-synthesized single crystals of PCN-608-
NH2 were immersed into a solution of H2BDC in DMF at 85
oC for 24 h before being washed three times with fresh DMF.
Single crystal X-ray diffraction experiments at 100 K reveal
Similarly, ionic mesoporous PCN-608 derivatives, PCN-
608-NH2-MPDC and PCN-608-NH2-SBDC, were also
obtained through solvent assisted installation of H2MPDC and
H3SBDC (Figure 2). The methyl and sulfonic groups on the
installed linkers are also seriously disordered because of the
high symmetry of the crystals. The counterions in the ionic
PCN-608 series MOFs are also located in the open 1D
channels along the c-axes (Figure 2). The analog of PCN-608-
NH2 with the amino groups replaced by methoxy groups,
PCN-608-OMe, is used for ionic linker installation in order to
avoid the influence of the active group in future applications (-
OMe is omitted from now on for brevity).
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Figure 3. UV-Vis spectra of DMF solutions of MLB+/OG2- in the presence of freshly prepared (a) PCN-700, (b) PCN-700-BDC, (c) PCN-
700-MPDC, (d) PCN-700-SBDC, (e) PCN-608, (f) PCN-608-BDC, (g) PCN-608-MPDC, and (h) PCN-608-SBDC. The prototype MOFs
PCN-700 and PCN-608, as well as PCN-700-BDC and PCN-608-BDC, which contain the electrically neutral linker BDC, adsorb neither
postively nor negatively charged organic dyes. The cationic microporous PCN-700-MPDC and mesoporous PCN-608-MPDC show
selective adsorption of the anionic dye OG2-. The anionic microporous PCN-700-SBDC and mesoporous PCN-608-SBDC show selective
adsorption of the cationic dye MLB+.
Additionally, PXRD patterns were obtained to verify the
successful installation of the ditopic linear linkers (Figure S11
and S14). According to powder X-ray diffraction data, the c-
axes of PCN-608-BDC, PCN-608-MPDC, and PCN-608-
SBDC (14.8063, 15.1671, and 15.0609 Å, respectively) are
slightly shortened compared with PCN-608 (15.6163 Å),
meaning the installation of the linear dicarboxylate ligands
was successful. 1H NMR spectra of the digested samples were
measured in order to figure out the linker ratio in the MOFs
(Figure 4c). As shown in Table S1, the linker ratios of the
H4TPCB ligand and the linear dicarboxylate ligands are all
approximately 1:1 in PCN-608 derivatives, which is consistent
with the calculated results from single crystal data.
charges, i.e. methylene blue (MLB+), sudan I (SDI0), and
orange G (OG2-) were selected for dye encapsulation in order
to verify the charges of the frameworks (Figure S15). It should
be noted that the anionic microporous and mesoporous MOF
samples were pretreated with dilute NaOH aqueous solution
before the ion exchange tests in order to replace the hydrogen
ions with sodium ions.
Fresh crystalline samples of PCN-700 and PCN-608 (~10
mg) were put into DMF solutions of MLB+, SDI0, and OG2-.
As expected, the concentrations of all three dyes in DMF
solutions were nearly constant after 20 hours, indicating that
the prototype MOFs possess electrically neutral frameworks
(Figure 3a, 3e, and S16). Additionally, the installation of the
uncharged H2BDC linker into the MOFs has no effect on the
chargeability of the prototype frameworks. As shown in
Figure S17, the concentrations of all the three kinds of dyes in
DMF solutions were nearly constant after fresh crystalline
samples of PCN-700-BDC and PCN-608-BDC (~10 mg) were
immersed into the solutions for 20 hours. However, when
fresh crystalline sample of PCN-700-MPDC and PCN-608-
MPDC (~10 mg) were immersed into the solutions for 20
hours, the concentrations of the anionic dye (OG2-) were
reduced to almost zero while the concentrations of the cationic
and neutral dyes (MLB+ and SDI0) remained nearly constant
(Figure S18). In addition, selectively capture of OG2- from a
mixture solution of OG2-/MLB+ was also observed for PCN-
700-MPDC and PCN-608-MPDC, indicating the cationic
nature of the frameworks after H2MPDC installation (Figure
3c & 3g). On the contrary, the concentrations of the anionic
and neutral dyes (OG2- and SDI0) were nearly constant while
the concentration of the cationic dye (MLB+) was almost
reduced to zero after fresh crystalline samples
It should be noted that the one pot synthesis of PCN-700-
MPDC, PCN-700-SBDC, PCN-608-MPDC, and PCN-608-
SBDC using a mixture of linkers was not successful. The
MPDC ligand is thermally labile and decomposes under
-
solvothermal synthesis. On the other hand, the -SO3 groups
tends to coordinate with Zr4+ during one-pot reactions to form
impurities. DMF was used as solvent during linker installation
to facilitate the deprotonation and the subsequent installation
of linear linkers. In theory, the process of neutral and ionic
linker installation in the zirconium-based MOFs can be
accelerate if the proto MOFs were pre-activated to remove the
coordinated solvents (-H2O/OH-), which has been
demonstrated in the literature.37-40 In our specific case, the
linker installation can readily occur in as-synthesized MOFs so
that the pre-activation was not used.
Selective Ion Exchange by Ionic MOFs. According to the
literature, charged MOFs have been considered as platforms
for selective, ion-exchange based encapsulation of organic
41-43
dyes.27,
Therefore, three organic dyes with different
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Figure 4. (a) N2 adsorption isotherms of PCN-608 and its derivatives show typical type IV isotherm shapes. (b) PXRD patterns of PCN-
608 and its derivatives after gas adsorption. (c) H NMR spectra of the digested samples for PCN-608 and its derivatives after gas
adsorption. The peaks marked with yellow asterisks should be attributed to the main ligand H4TPCB; part of the green asterisk marked
peak should be attributed to the neutral linear linker H2BDC; the light blue asterisk marked peaks should be attributed to the positively
charged linear linker H2MPDC; and the orange asterisk marked peaks should be attributed to the negatively charged linear linker H2SBDC.
1
of PCN-700-SBDC and PCN-608-SBDC (~10 mg) were
immersed into the solutions for 20 hours (Figure S19).
Moreover, selectively capture of MLB+ from a mixture
solution of OG2-/MLB+ was also observed for PCN-700-
SBDC and PCN-608-SBDC, indicating the anionic nature of
the frameworks after H3SBDC installation (Figure 3d & 3h).
MOFs after activation under high vacuum (Figure 4c).
Furthermore, TGA curves of MOF samples before and after
insertion of linkers were monitored (Figure S23). The weight
loss before 300 oC was attributed to the removal of
coordinated water or terminal ligands on the Zr6 cluster. PCN-
608-BDC shows reduced water loss, which is in line with the
replacement of terminal H2O/OH- by BDC linker. PCN-608-
SBDC gradually loss water at a lower temperature (before 200
oC), which can be attributed to the removal of Na+ coordinated
water in the cavity. The methylpyridinium moieties in PCN-
608-MPDC are thermally labile, which decomposes at much
lower temperature (before 150 oC) compared with other
samples.
Porosity Analysis and Stability Tests The N2 adsorption
isotherms were measured for PCN-608 and its derivatives in
order to investigate the influence of linker installation on MOF
porosity (Figure 4a). Although the saturated N2 uptake amount
decrease significantly after linker installation, all four
adsorption isotherms belong to the typical IV isotherm type,
indicating the mesoporous nature of the MOFs. The N2
adsorption amount of PCN-608-SBDC is similar to that of
PCN-608-BDC, which may be because some BDC ligands are
encapsulated in the pores. Pore size distribution of PCN-608
and its derivatives were also analyzed by NLDFT methods
based on the N2 sorption data, indicating the mesoporosity of
the four MOFs (Figure S20). The BET surface areas and pore
volumes of the MOFs decrease after neutral and ionic linker
installation, while the pore size distributions shift slightly
(Table S2). In short, mesopores can survive in the PCN-608
2+
Immobilization of Cationic Ru(bpy)3 Catalysts in
2+
Anionic PCN-608-SBDC. Ru(bpy)3 has received much
attention because of its distinct photocatalytic properties.44-46
2+
-
Commonly used Ru(bpy)3
contains Cl- or PF6 as
conterions.47 These kind of photocatalysts show high activity
under both UV and visible light. However, the recyclability of
this expensive compound is not easy due to its exceptional
solubility in commonly used solvents. Considering the
coexistence of mesopores and ionic framework in PCN-608
series MOFs, the anionic mesoporous MOF PCN-608-SBDC
was chosen to encapsulate Ru(bpy)32+ cations. In this way, the
photocatalyst can be accessed by substrate in the mesopores
1
series MOFs after installation of neutral or ionic linkers. H
NMR spectra of the digested samples after gas adsorption
were measured, showing the integrity of the multicomponent
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and the photocatalyst can be retained inside of the pores and
further reused after the product is separated.
linkers into two prudently selected prototype frameworks
(PCN-700 and PCN-608). The topologies of the parent MOFs
changed due to the increase in connection number of the Zr6
cluster from 8-c to 10-c, while the porosity of the networks
was retained. Selective ion exchange-based dye capture shows
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As-synthesized PCN-608-SBDC was immersed into an
aqueous solution of Ru(bpy)3Cl2 after pretreatment with dilute
2+
NaOH solution. The cation exchange based Ru(bpy)3
2+
the ionicity of the MOFs. Ru(bpy)3 cations can be
adsorption was monitored by UV-Vis spectra (Figure S21).
The Ru(bpy)32+ adsorption amount in PCN-608-SBDC is about
16 mg / 100 mg after 48 hours, which is consistent with the
encapsulated into the anionic mesoporous PCN-608-SBDC
and the resulting hybrid photocatalyst shows high catalytic
activity and recyclability. Our research sheds light on the
design and synthesis of ionic MOFs, as well as the precise
regulation of pore environments in both microporous and
mesoporous MOFs.
theoretical results from single crystal data supposing each two
2+
sodium ions exchange with one Ru(bpy)3
ion. The
9
photocatalytic activity of the hybrid Ru(bpy)3@PCN-608-
SBDC was tested by an aza-Henry reaction as a model
reaction under visible light. As shown in Table 1, the chloride
salt Ru(bpy)3Cl2 shows very high conversion yield for the aza-
Henry reaction, which is consistent with that of previous
reports. However, the catalyst dissolves in the nitromethane
solvent and could not be recycled by centrifugation.
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ASSOCIATED CONTENT
Supporting Information.
The Supporting Information is available free of charge via the
Internet at http://pubs.acs.org.
Text, tables, and figures giving experimental procedures for the
syntheses of the ligands, PXRD, N2 adsorption isotherms, 1H
NMR spectra, and other additional information (PDF)
X-ray crystallographic details of the structures (CIF)
Table 1. Aza-Henry reactions catalyzed by the hybrid
photocatalyst Ru(bpy)3@PCN-608-SBDC
AUTHOR INFORMATION
Corresponding Author
*ydq@fjirsm.ac.cn
*zhou@chem.tamu.edu
conversion yields (%)b
catalyst
Ru(bpy)3Cl2
PCN-608
substratea
run 1
99
run 2
N.A.
N.A.
N.A.
99
run 3
N.A.
N.A.
N.A.
93
Author Contributions
#J.P. and S.Y. contributed equally.
Notes
1a
1a
1a
1a
1b
1c
18
The authors declare no competing financial interest.
PCN-608-SBDC
17
98
ACKNOWLEDGMENT
Ru(bpy)3@PCN-
608-SBDC
98
97
96
The gas sorption studies were supported by the Center for Gas
Separations Relevant to Clean Energy Technologies, an Energy
Frontier Research Center funded by the U.S. Department of
Energy, Office of Science, Office of Basic Energy Sciences (DE-
SC0001015). Structural analyses were supported by the Robert A.
Welch Foundation through a Welch Endowed Chair to HJZ (A-
0030). The National Science Foundation Graduate Research
Fellowship (DGE: 1252521) is gratefully acknowledged. The
authors also acknowledge the financial support of the U.S.
Department of Energy Office of Fossil Energy National Energy
Technology Laboratory (DEFE0026472) and National Science
Foundation Small Business Innovation Research (NSF-SBIR)
program under Grant No. (1632486). The authors also
acknowledge the financial supports of the Key Research Program
of Frontier Sciences of the Chinese Academy of Sciences
(QYZDB-SSW-SLH019 and QYZDY-SSW-SLH025), 973
Program (2014CB932101 and 2013CB933200), National Nature
Science Foundation of China (21771177, 21390392 and
21371169), Youth Innovation Promotion Association CAS, and
Chun Miao Project of Haixi Institutes (CMZX-2016-001). The
powder diffractions were carried out at the Advanced Photon
Source on beamline 17-BM-B with the kind assistance of Andrey
Yakovenko. S. Yuan also acknowledges the Dow Chemical
Graduate Fellowship.
97
98
93
a For the substrate and the product, 1a, 2a, R = H; 1b, 2b, R =
Br; 1c, 2c, R = OCH3. b Conversion yields were determined by
1H NMR of the crude product.
The conversion yield of the aza-Henry reaction catalyzed by
the hybrid photocatalyst was almost as high as that of the
2+
chloride salt, when the Ru(bpy)3 cation was encapsulated
into the mesopores of the anionic PCN-608-SBDC. Three
substrates with different substituents were applied in the
photocatalytic reaction in order to investigate the wide
applicability of the new catalyst. The catalytic activities of
Ru(bpy)3@PCN-608-SBDC for the three substrates are all
very high (Table 1). Moreover, the catalyst has been tested for
three cycles without an obvious decrease in the conversion
yield, indicating that Ru(bpy)3@PCN-608-SBDC is
a
promising reusable photocatalyst. Additionally, taking the
substrate 1b as an example, catalytic conversion was
monitored as a function of time (Figure S24). The conversion
steadily increases within 1 hour and then level off.
Furthermore, powder X-ray diffraction patterns of the hybrid
photocatalyst were measured after three cycles of catalytic
reactions, corroborating the stability of the material (Figure
S22).
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