Tuning the Dimensionality of Interpenetration in a Pair of Framework-Catenation Isomers to Achieve Selective Adsorption of CO2 and Fluorescent Sensing of Metal Ions

Article abstract of DOI:10.1021/acs.inorgchem.5b00934

A pair of framework-catenation isomers (UPC-19 and UPC-20) based on an anthracene-functionality dicarboxylate ligand were synthesized and characterized for the first time through tuning of the dimensionality of interpenetration. The interpenetration dimen

Full text of DOI:10.1021/acs.inorgchem.5b00934

Communication
pubs.acs.org/IC
Tuning the Dimensionality of Interpenetration in a Pair of
Framework-Catenation Isomers To Achieve Selective Adsorption of
CO2 and Fluorescent Sensing of Metal Ions
Rongming Wang, Minghui Zhang, Xiaobin Liu, Liangliang Zhang,* Zixi Kang, Wen Wang,
Xiaoqing Wang, Fangna Dai, and Daofeng Sun*
State Key Laboratory of Heavy Oil Processing, College of Science, China University of Petroleum (East China), Qingdao, Shandong
266580, People’s Republic of China
S
* Supporting Information
secondary building units (SBUs), reducing reagent concen-
ABSTRACT: A pair of framework-catenation isomers
(UPC-19 and UPC-20) based on an anthracene-
functionality dicarboxylate ligand were synthesized and
characterized for the first time through tuning of the
dimensionality of interpenetration. The interpenetration
dimensionality significantly influences the properties
including the porosity, gas-uptake capacity, and fluorescent
sensing ability: UPC-19 with 5-fold interpenetration is
nonporous, whereas the 3-fold interpenetration form of
UPC-20 is porous and exhibits selective adsorption of CO2
and fluorescent sensing of Cu2+ and Fe3+ through
fluorescence quenching.
trations, using liquid-phase epitaxy, and introducing template
molecules were successfully applied in the control of inter-
penetration in MOFs.9,10 Recently, Hupp and our group
reported a strategy that used organic ligand with hindrance
groups to suppress the formation of interpenetrating frame-
works.11 Because the interpenetrating and noninterpenetrating
frameworks showed quite different structural features, the
control of interpenetration or tuning of the dimensionality of
interpenetration in MOFs could generate porous MOF materials
that exhibit unexpected properties including gas adsorption/
separation, catalysis, and fluorescent sensor. However, studies on
the tuning of the dimensionality of interpenetration in MOFs are
seldom reported to date.12 In this Communication, we report a
pair of framework-catenation isomers, Zn4O(LOMe)3 (UPC-19)
and Zn4O(LOMe)3·7H2O (UPC-20), with different dimension-
alities of interpenetration (Scheme 1). Furthermore, the isomer
showed different gas-absorption and fluorescent-sensing proper-
ties.
elective adsorption of CO2 from flue gas using porous
Smaterials through physisorption is one of the most efficient
and low-cost strategies to prevent global warming.1 Currently,
the widely used porous materials include zeolites, active carbons,
and nanotubes.2 Although some of these porous materials exhibit
high stability and gas-uptake capacity, the low selectivity to CO2
is the insuperable drawback for these materials in the application
of CO2 capture. Hence, developing new porous materials with
high selectivity and gas-uptake capacity to CO2 is still an
extremely challenging task.
Scheme 1. Schematic Representation of H2LOMe and
Formation of Two Interpenetration Frameworks with
Different Dimensionalities Controlled by the Temperature
and Solvents
Metal−organic frameworks (MOFs) are a new type of porous
material that is built from metal-based nodes and organic linkers
and possesses potential applications in gas storage, catalysis,
electronics, and drug delivery.3,4 Recently, the studies of porous
MOFs on the application of selective adsorption/capture have
been increasing year by year.5,6 On the basis of current research,
one of the strategies to build porous MOFs with selective
adsorption of CO2 is to use the interpenetration nature of the
frameworks, through which the pore size and geometry can be
fully tuned and decorated to meet the requiring character for
selective adsorption of CO2.7 Actually, interpenetration is a very
common phenomenon in the construction of porous MOFs. In
some cases, the generation of interpenetration in MOFs can
significantly reduce the porosity to result in the formation of a
nonporous framework,8 although the single framework exhibits
large channels. Hence, research on the control of inter-
penetration or tuning of the interpenetration dimensionality is
very important for the construction of porous MOFs. In the past
decade, several strategies such as applying rigid-rod-shaped
UPC-19 possesses a 5-fold interpenetrating framework with a
pcu net, which is similar to the well-known MOF-5 series.13 The
Zn4O(COO)6 SBUs generated from the linkage of six
carboxylate groups are connected by LOMe ligands to generate
an open framework with 3D channels (Figure S1a,b in the
Supporting Information, SI). The dimensions of the channels are
19.2 × 11.9 Å. Because of the existence of large channels in the
Received: April 27, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b00934
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Inorganic Chemistry
Communication
single net of UPC-19, five such nets interpenetrate mutually to
provide a 3D dense structure with a 5-fold interpenetrating
framework (Figure S1c in the SI). There are no obvious
hydrogen-bonding or π···π interactions among the ligands in
different nets.
confirm the performance of UPC-20, ideal adsorbed solution
theory (IAST) was applied to evaluate the mixed-gas adsorption
behavior. As shown in Figure 1, the selectivities of UPC-20 for
UPC-20 exhibits a 3-fold interpenetrating framework based on
a single net similar to that of UPC-19. Thus, UPC-19 and UPC-
20 are a pair of framework-catenation isomers with different
dimensionalities. In the crystal structure of UPC-20, there are
two independent asymmetric units (A and B), forming two
independent nets. As shown in Figure S2 in the SI, LOMe ligands
in A and B units are slightly distinct: the two benzene rings are
almost vertical with the central anthracene ring, with average
dihedral angles of 70.8° in unit A and 84.4° in unit B. The ligands
in unit A link the Zn4O(COO)6 SBUs to generate a 3D open
framework with a pcu net that is similar to the single net in UPC-
19, whereas the ligands in unit B connect the Zn4O(COO)6
SBUs to give rise to a 3D framework that is different from the
single net in UPC-19. Accordingly, two nets generated from unit
A interpenetrate each other, providing a 2-fold interpenetrating
framework, which further interpenetrates with the other net
arising from unit B to result in the final 3-fold interpenetrating
structure. The C−H···π interactions (3.79 Å) among the LOMe
ligands in different nets further stabilize the whole framework
(Figure S3 in the SI). Despite the existence of interpenetration,
UPC-20 exhibits 1D channels along the [101] direction due to
the low interpenetration dimensionality compared to that of
UPC-19. After removal of guest solvents, a total solvent-
accessible volume of 38.6% was calculated based on the
PLATON/VOID routine for UPC-20.14
Figure 1. (a) CO2/N2 sorption isotherms at 273 K. (b) CO2/CH4
sorption at 273 K. (c and d) IAST CO2/N2 and CO2/CH4 selectivities
for 10:90 CO2/N2 and CO2/CH4 mixtures, respectively, at 273 K.
CO2 over CH4 and N2 under 10:90 CO2/CH4 and CO2/N2 gas
mixtures are 5 and 15, respectively. In the past decade, although a
large amount of literature reported control or tuning of the
interpenetration in MOFs, achieving selective gas adsorption
through tuning of the dimensionality of interpenetration in a pair
of framework-catenation isomers remains unexplored prior to
this work, to the best of our knowledge.
The porosities of the final frameworks in UPC-19 and UPC-
20 were also investigated by gas-uptake measurements. As
expected, a restricted adsorption behavior of UPC-19 was
observed for the N2 adsorption isotherm at 77 K. A similar result
was also found for CO2 adsorption, as shown in Figure S4 in the
SI, which is in agreement with the result from the crystal
structure. In contrast, the N2 adsorption isotherm at 77 K for
UPC-20 exhibits a reversible type I behavior, indicating its
permanent porosity. The Brunauer−Emmett−Teller surface
area calculated from the N2 isotherm is 697.4 m2 g−1, with a pore
volume of 0.37 cm3 g−1. Importantly, UPC-20 can adsorb 42.7
cm3 g−1 of CO2 at 273 K, further confirming its porosity. In
addition, various gas-uptake measurements including H2 at 77
and 87 K, CO2 at 295 K, and CH4 and N2 at 273 K were carried
out for UPC-20. H2 adsorption isotherms at 77 and 87 K also
exhibit reversible type I behavior, with the largest amounts of
adsorption being 91 and 64 cm3 g−1, respectively. The
corresponding heat of adsorption (Qst) for H2 was calculated
by fitting the H2 adsorption isotherms at 77 and 87 K to a Virial-
type expression. At the lowest coverage, Qst for H2 was calculated
to be ∼5.4 kJ mol−1, which is comparable to those of MOF-5 (4.7
kJ mol−1) and MOF-177 (4.4 kJ mol−1).15 The CO2 sorption
measurements revealed that UPC-20 can adsorb 42.7 and 22.3
cm3 g−1 of CO2 at 273 and 295 K, respectively, with a calculated
Qst of 16.7 kJ mol−1. The Qst value for CO2 is comparable to that
of Zn4O(FMA) (16.1 kJ mol−1),16 which is the isoreticular
structure with UPC-20.
Another potential application for MOF materials is the
fluorescent sensing of metal ions, organic molecules, etc., which
have been widely studied in recent years.17,18 Considering that
the LOMe ligand contains methoxy groups that can chelate metal
ion,19 the fluorescent sensing of metal ions was carried out for
UPC-19 and UPC-20. As expected, UPC-19 and UPC-20
showed quite different sensing abilities: UPC-20 can selectively
sense Cu2+ and Fe3+ ions through fluorescent quenching,
whereas UPC-19 cannot. In the measurement, we select
dimethyl sulfoxide (DMSO) as the standard emulsion. The
freshly prepared samples of UPC-19 and UPC-20 were ground
and suspended in a DMSO solution, to which was added
different metal ions dropwise in DMSO (1 mM). Interestingly, as
shown in Figure 2, there is a slight effect on the luminescence
intensity of UPC-19 after the addition of Li+, Ag+, Cd2+, Al3+,
Cu2+, and Fe3+. In contrast, the addition of Cu2+ and Fe3+ to the
UPC-20 emulsion can quench the luminescence significantly,
indicating selective sensing of Cu2+ and Fe3+ through fluorescent
quenching. The different sensing abilities to metal ions for UPC-
19 and UPC-20 should derive from their structural features. As
mentioned above, UPC-19 is nonporous and thus metal ions
cannot contact with the methoxy groups, whereas UPC-20 is
porous and metal ions can enter into the channels to interact with
the methoxy groups.
However, UPC-20 can only adsorb 9.4 cm3 g−1 of CH4 at 273
K, which may be due to the polar environment raised from the
functionalized methoxy groups in the cavities of UPC-20.
Accordingly, there is also no obvious adsorption of N2 (only 2.9
cm3 g−1) at 273 K. These results indicate that UPC-20 can
selectively adsorb CO2 over N2 and CH4 at 273 K. To further
In conclusion, a pair of framework-catenation isomers (UPC-
19 and UPC-20) was synthesized and characterized based on an
anthracene-functionality dicarboxylate ligand and Zn4O(COO)6
SBUs with tuning of the interpenetration dimensionality, which
is controlled by both the temperature and solvents used in the
synthesis of the complexes. UPC-19 with 5-fold interpenetration
B
DOI: 10.1021/acs.inorgchem.5b00934
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on achieving selective adsorption of CO2 and selective sensing of
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synthesis of a noninterpenetrating framework that is a single net
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ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray crystallographic data in CIF format, materials, methods
and characterization, experimental section, and supplementary
structure figures. The Supporting Information is available free of
charge on the ACS Publications website at DOI: 10.1021/
acs.inorgchem.5b00934.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: liangliangzhang@upc.edu.cn.
*E-mail: dfsun@upc.edu.cn.
■
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the NSFC (Grants 21371179 and
21271117), Grant NCET-11-0309, the Shandong Natural
Science Fund for Distinguished Young Scholars (Grant
JQ201003), the Shandong Provincial Natural Science Founda-
tion (Grant ZR2010BL011), and the Fundamental Research
Funds for the Central Universities (Grants 13CX05010A,
14CX02150A, and 14CX02158A).
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DOI: 10.1021/acs.inorgchem.5b00934
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