Synthesis, structure and gas adsorption properties of a stable microporous Cu-based metal-organic framework assembled from a T-shaped pyridyl dicarboxylate ligand

Article abstract of DOI:10.1039/c7ra01125c

A three-dimensional microporous metal-organic framework assembled from a T-shaped pyridyl dicarboxylate ligand, 4′-(pyridin-4-yl)-[1,1′-biphenyl]-3,5-dicarboxylic acid (H₂PBPD), has been successfully synthesized via solvothermal reaction with copper(ii) nitrate. Compound 1 was characterized by X-ray single-crystal diffraction, elemental analysis, IR spectroscopy and thermogravimetric analyses. Single-crystal X-ray diffraction analysis indicates that compound 1 is a (3,6)-connected three-dimensional framework with the point symbol {4²·6}₂{4⁴·6²·8⁶·10³}. In the framework of this compound, there exist two large metal-ligand cages. Stability tests show that compound 1 keeps its crystal structure after being soaked in several organic solvents or calcined at 250 °C under air atmosphere. The N₂ adsorption at 77 K shows that compound 1 is microporous with a BET surface area of 1682 m² g^?1. Compound 1 possesses high adsorption capacities for CO₂ (114 cm³ g^?1, 273 K) under ambient pressure. The test of CO₂ cyclic adsorption and regeneration of 1 shows that it has a stable CO₂ adsorption capacity and no obvious weight change after doing this ten times.

Full text of DOI:10.1039/c7ra01125c

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Synthesis, structure and gas adsorption properties
of a stable microporous Cu-based metal–organic
framework assembled from a T-shaped pyridyl
dicarboxylate ligand†
Cite this: RSC Adv., 2017, 7, 17697
*
Di Wang, Libo Sun, Yuchuan Liu, Jianfeng Du, Shun Wang, Xiaowei Song
*
and Zhiqiang Liang
A
three-dimensional microporous metal–organic framework assembled from
a
T-shaped pyridyl
dicarboxylate ligand, 40-(pyridin-4-yl)-[1,10-biphenyl]-3,5-dicarboxylic acid (H2PBPD), has been
successfully synthesized via solvothermal reaction with copper(II) nitrate. Compound 1 was characterized
by X-ray single-crystal diffraction, elemental analysis, IR spectroscopy and thermogravimetric analyses.
Single-crystal X-ray diffraction analysis indicates that compound
1 is a (3,6)-connected three-
dimensional framework with the point symbol {42$6}2{44$62$86$103}. In the framework of this
compound, there exist two large metal–ligand cages. Stability tests show that compound 1 keeps its
crystal structure after being soaked in several organic solvents or calcined at 250 ꢀC under air
atmosphere. The N2 adsorption at 77 K shows that compound 1 is microporous with a BET surface area
Received 25th January 2017
Accepted 10th March 2017
of 1682 m2 ꢁ1. Compound 1 possesses high adsorption capacities for CO2 (114 cm3 ꢁ1, 273 K) under
g g
DOI: 10.1039/c7ra01125c
ambient pressure. The test of CO2 cyclic adsorption and regeneration of 1 shows that it has a stable CO2
rsc.li/rsc-advances
adsorption capacity and no obvious weight change after doing this ten times.
The structure and properties of MOFs can be rationally
designed and improved through several effective approaches
Introduction
such as incorporation of open metal sites, ligand functionali-
zation, framework interpenetration and polar pore walls.5
Generally, the pores of MOFs are lled with terminal and free
solvent molecules, which could be removed by solvent-
exchanged and thermal treatment to generate open metal
sites. Functionalized organic ligands can be obtained by intro-
ducing some groups, such as –NH2, –OH, –CH3 and pyridyl
groups.6 And it is worth noting that embedding Lewis basic
pyridyl sites into the pore walls of MOFs can drastically impact
their gas uptake capacity and selectivity, especially for the CO2
capture, which is because there are dipole–quadrupole inter-
actions between the polarizable CO2 molecule and the nitrogen
site.7 In addition, the coordination modes of ligands with
specic symmetries are a key factor in the structures and
properties of the nal products.
In recent years, MOFs with carboxylate-containing ligands
which contain mixed N-, O-donors have been extensively
studied. Among these ligands, the N-donors mainly come from
compounds with coordination such as pyridine, imidazole, tri-
azole and so on, and the O-donors come from groups –COOH,
–OH or nitrogen oxides.8 A series of T-shaped pyridyl dicarboxylate
ligand such as 5-(pyridin-4-yl)isophthalic acid, (E)-5-(pyridin-4-
yl-methyleneamino)isophthalic acid, 5-(isonicotinamido)iso-
phthalic acid, 5-[(pyridin-4-ylmethyl)amino]isophthalic acid, 5-(4-
As an emerging class of porous solid materials, metal–organic
frameworks (MOFs) that are self-assembled from metal ions or
clusters with organic linkers, have attracted considerable
attention owing to their great potential in a wide variety of
applications.1 Among the diverse applications of MOFs, gas
storage and separation will probably play a key role in future
due to the rising energy and environment issues faced by our
society.2 The extremely high surface areas, adjustable pore sizes,
as well as intriguing functionalities make them more competi-
tive over other traditional adsorbent materials, such as zeolites,
activated carbons, or diatomite.3 Despite this, the poor stability
of MOFs has been recognized to be a major drawback for their
practical applications. For this, scientists have proposed some
strategies for enhancing the stability of MOFs,4 how to design
and synthesize stable MOFs materials with high capacity of gas
adsorption and separation became the focus of research.
State Key Lab of Inorganic Synthesis and Preparative Chemistry, Jilin University,
Changchun, 130012, P. R. China. E-mail: liangzq@jlu.edu.cn; xiaoweisong@jlu.edu.
cn
† Electronic supplementary information (ESI) available: Complete X-ray
crystallographic data for 1 in CIF format. PXRD patterns, TGA and IR spectra
for 1. Selected bond lengths and angles for compound 1. CCDC 1471464. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c7ra01125c
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 17697–17703 | 17697

View Article Online
RSC Advances
Paper
pyridyl)-methoxyl isophthalic acid and 40-(1H-tetrazol-5-yl)-[1,10- and rened anisotropically on F2 by the full-matrix least-squares
biphenyl]-3,5-dicarboxylic acid (H3TZBPDC), etc. have been used technique using the SHELXL-97.13 All non-hydrogen atoms were
to construct new structures with diverse properties.9 This type of rened anisotropically. The hydrogen atoms on the aromatic
ligands were selected based on the following considerations: (1) rings were geometrically placed with isotropic thermal param-
carboxylate groups and pyridine nitrogen donors in the ligand can eters 1.2 times that of the attached carbon atom. The diffraction
take part in coordination as bridging ligands to form metal- data of compound 1 were collected by using the SQUEEZE
carboxylate clusters, such as dinuclear, trinuclear, and even routine of PLATON to remove the contribution of disordered
higher nuclear clusters; (2) pyridyl donor organic ligands can molecules.14 Crystallographic data for compound
1 are
complement the dicarboxylate ligands in the coordination and summarized in Table S1,† while the selected bond lengths and
formation of high-connected nets; (3) the N-donors from the angles are list in Table S2.† More details on the crystallographic
ligands can coordination with the metal cations, forming much studies as well as atom displacement parameters are presents in
stronger metal-N bonds, which would enable the high stability of the CIF.
the resultant MOF.
By taking account of the above-mentioned factors, we designed
Synthesis of 40-(pyridin-4-yl)-[1,10-biphenyl]-3,5-dicarboxylic
acid (H2PBPD)
and synthesized a novel T-shaped pyridyl dicarboxylate ligand
named
40-(pyridin-4-yl)-[1,10-biphenyl]-3,5-dicarboxylic
acid
The synthetic route of compound 1 is shown in Scheme 1. To
a solution of dimethyl 5-iodoisophthalate (320 mg, 1.0 mmol) in
DMF (5 mL) were sequentially added 4-bromophenylboronic
acid (210 mg, 1.05 mmol), Pd(PhCN)2Cl2 (20 mg, 0.053 mmol)
and K2CO3 (400 mg, 2.90 mmol) under N2. Aer 12 hours stirred
at 80 ꢀC under N2, the reaction was quenched with water,
extracted with ethyl acetate, washed with brine and dried over
MgSO4. Evaporation and ash column chromatography on
a silica gel (petroleum ether–ethyl acetate ¼ 10 : 1) gave the
coupling product M1 (180 mg, 0.52 mmol) in 52% yield as a pale
(H2PBPD) via Suzuki coupling reaction in this work. Based on the
H2PBPD ligand, a stable three-dimensional microporous metal–
organic framework [Cu(PBPD)(DMF)2(H2O)3] (1) has been
successfully synthesized via a solvothermal reaction with cop-
per(II) nitrate. In the framework of this compound, there exist two
large metal–ligand cages. We explored the stability and adsorp-
tion capacity of compound 1. The stability analyses indicates that
compound 1 can keep its crystal structure aer being soaked in
several organic solvents or calcined at 250 ꢀC under air atmo-
sphere, and even aer cycle more than 10 times. The N2 adsorp-
tion at 77 K shows compound 1 is microporous with BET surface
area of 1682 m2 gꢁ1. And compound 1 possesses high adsorption
capacities for CO2 (114 cm3 gꢁ1, 273 K) under ambient pressure.
In preparation of this paper, Bai et al. reported a similar MOF
showing good CH4 storage capacity under high pressure.10
1
solid. H NMR (300 MHz, CDCl3): d ¼ 8.66 (t, J ¼ 1.5 Hz, 1H),
8.42 (d, J ¼ 1.8 Hz, 2H), 7.50–7.64 (m, 4H). 13C NMR (75 MHz,
CDCl3): d ¼ 166.1, 140.8, 138.0, 132.2, 132.0, 131.4, 129.6, 128.7,
122.7, 52.5. Anal. calcd for C16H13BrO4: C, 55.04; H, 3.75.
Found: C, 55.03; H, 3.51. MS m/z: 351.0 (M + H+, 81Br), 349.0 (M +
H+, 79Br).
To this product of M1 (710 mg, 2 mmol), dissolved in DMF
(10 mL), were added pyridin-4-ylboronic acid (370 mg, 3 mmol),
Pd(PPh3)4 (231 mg, 0.2 mmol) and K2CO3 (552 mg, 4 mmol)
under N2. Aer stirring at 120 ꢀC under N2 for 12 hours, the
reaction was quenched with water, recrystallized with ethyl
acetate, gave the coupling product dimethyl 40-(pyridin-4-yl)-
[1,10-biphenyl]-3,5-dicarboxylate (M2) (426 mg, 1.22 mmol) in
Experimental section
Materials and physical characterizations
Except for the H2PBPD ligand, all other chemicals and solvents
were obtained from commercial sources and used as received
without further purication. Powder X-ray diffraction (PXRD)
data were collected on a Rigaku D-Max 2550 diffractometer
using Cu-Ka radiation (l ¼ 0.15418 nm) and 2q ranging from 4
to 40ꢀ at room temperature. IR spectra were recorded on
a Nicolet Impact 410 FTIR spectrometer as KBr pellets in the
400–4000 cmꢁ1 region. Thermogravimetric analyses (TGA) data
were recorded on Perkin-Elmer TGA Q500 thermogravimetric
analꢀyzer under an air atmosphere from room temperature to
800 C (heating rate of 10 C minꢁ1). Elemental microanalyses
ꢀ
(C, H and N) were carried out using a Perkin-Elmer 2400
elemental analyzer. The point symbol and topological analysis
were conducted using the TOPOS 4.0 program package.11
Crystal structure determination
The diffraction data of compound 1 were collected on a Bruker
AXS SMART APEX-II diffractometer with graphite mono-
˚
chromated Mo Ka radiation (l ¼ 0.71073 A) at 298 K. Date
processing was completed with the SAINT processing
program.12 The crystal structures was solved by direct methods, Scheme 1 Design and synthesis of ligand H2PBPD.
17698 | RSC Adv., 2017, 7, 17697–17703
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
61% yield as a pale solid. 1H NMR (300 MHz, CDCl3): d ¼ 8.70 (s, TGA Q500 thermogravimetric analyzer. The sample was pre-
1H), 8.68 (t, J ¼ 1.5 Hz, 2H), 8.51 (d, J ¼ 1.4 Hz, 2H), 7.82–7.74 treated at 150 ꢀC under N2 atmosphere for ve hours to remove
(m, 4H), 7.58–7.53 (m, 2H), 3.99 (s, 6H). 13C NMR (75 MHz, the guest molecules in the pores. The conditions of test was 25
ꢀ
CDCl3): d ¼ 166.1, 150.4, 147.5, 141.0, 139.8, 138.0, 132.2, 131.4, to 80 C at ambient pressure.
129.7, 127.9, 127.7, 121.5, 52.4. Anal. calcd for C21H17NO4: C,
72.61; H, 4.93; N, 4.03. Found: C, 71.62; H, 4.98, N, 3.36. MS m/z:
348.1 (M + H+).
Results and discussion
Crystal structure descriptions
To this product of M2 (0.96 g, 2.55 mmol), dissolved in THF–
H2O, (1 : 1, 20 mL) was added KOH (1.428 g, 25.5 mmol) and the
Single-crystal X-ray structural analysis shows that compound 1
possesses 3D neutral framework and crystallizes in the hexag-
resulting solution was stirred under reux for 24 h. The mixture
was acidied with aq. HCl, and then ltered. The pure product
H2PBPD was obtained as a pale yellow solid. 1H NMR (300 MHz,
DMSO-d6): d ¼ 9.00 (d, J ¼ 6.3 Hz, 2H), 8.47–8.55 (m, 5H), 8.21
(d, J ¼ 8.1 Hz, 2H), 8.03 (d, J ¼ 8.4 Hz, 2H). 13C NMR (75 MHz,
DMSO-d6): d ¼ 166.3, 154.7, 142.0, 141.3, 139.6, 133.9, 132.3,
131.4, 128.9, 128.0, 123.8. Anal. calcd for C19H13NO4: C, 71.47;
H, 4.10; N, 4.39. Found: C, 71.62; H, 4.98, N, 3.36. MS m/z: 320.4
(M + H+).
ꢀ
onal space group R3. The asymmetric unit of 1 contains one
independent Cu atom and one PBPD2ꢁ ligand. As shown in
Fig. 1a, the two carboxyl groups of PBPD2ꢁ ligand display the
bridging coordination mode to link two Cu2+ ions, and the N
atom of pyridine is coordinated with one Cu2+ ion. Fig. 1b shows
that two Cu2+ ions are chelated by four carboxylate groups from
four different PBPD2ꢁ ligands to form a square paddle-wheel
binuclear Cu2(COO)4 cluster, and the axial positions of the
cluster are occupied by two pyridine-N donors from another two
PBPD2ꢁ ligands. As shown in Fig. 1c, the six-connected paddle-
wheel clusters are linked together through three-connected
PBPD2ꢁ ligands to form a 3D structure, with 1D channels
Synthesis of [Cu(PBPD)(DMF)2(H2O)3] (1)
A mixture of Cu(NO3)2$3H2O (6.05 mg, 0.025 mmol), H2PBPD
(7.975 mg, 0.025 mmol), DMF (1 mL) and HNO3 (125 mL, 2.7 M
ꢀ
in DMF) was sealed in a 20 mL vial and heated at 85 C for 4
˚
along the c-axis (8.468 A). The Cu–O bond lengths varies from
days. Aer slowly cooling to room temperature, green diamond-
shaped crystals of 1 were isolated (yield: 25%). Anal. calcd for
˚
˚
1.954(3) to 1.970(3) A, the Cu–N bond length is 2.188(3) A, and
the O–Cu–O bond angles are in the range of 88.50(14)–
166.82(11)ꢀ (Table S2†), which are comparable to those values
found in other reported similar compounds.16,9b,9d There are two
types of metal–ligand cages in the framework of compound 1.
The small cage is constructed by six paddle-wheel [Cu2(CO2)4]
clusters and six PBPD2ꢁ ligands with dimensions of ca. 8.5 ꢂ
C
25H31N3O9Cu: C, 51.69%; H, 5.37%; N, 7.23%; found: C,
52.11%; H, 4.69%; N, 7.11%. IR spectrum (cmꢁ1): 2928(m),
1672(s), 1493(w), 1372(s), 1250(w), 1090(s), 997(w), 912(w),
819(s), 771(s), 725(s), 649(m), 584(w), 491(m).
Stability test for 1
˚
15.3 A (Fig. 2a). The large cage consists of twelve paddle-wheel
[Cu2(CO2)4] clusters and six PBPD2ꢁ ligands with dimensions
The as-synthesized sample was soaked in organic solvents such
as CH3OH, C2H5OH, CH2Cl2, CHCl3 and CH3CN for more than
two months, then ltered and dried for further characterization
of PXRD. In addition, the dried as-synthesized samples were
heat at different temperature for 30 min with the heating rate of
5 C minꢁ1, then the PXRD was also measured to characterize
ꢀ
the thermal stability.
Sample activation and adsorption measurements
The solvent-exchange sample was obtained by soaking the as-
synthesized sample in methanol for three days with methanol
refreshing every two hours, and then replace methanol with
dichloromethane in the same method for three days. Before gas
adsorption measurement, the sample was future activated
using the “outgas” function of the adsorption analyzer to
remove the guest molecules from the pores by evacuation under
a dynamic vacuum at 85 ꢀC for 10 h. All gases used are of
99.999% purity throughout the adsorption measurements. Low-
pressure nitrogen (N2), carbon dioxide (CO2) sorption experi-
ments were performed on Micrometrics ASAP 2020 instrument,
and methane (CH4) sorption experiments were performed on
Micrometrics ASAP 2420 instrument. The selectivity of CO2 over
CH4 was calculated by using the ideal adsorption solution
theory (IAST).15 The experiment of CO2 cyclic adsorption and
Fig. 1 (a) Coordination modes of carboxyl groups of PBPD2ꢁ ligand.
(b) The distorted binuclear [Cu2(COO)4] motif. (c) View of the 3D
porous network along the c-axis in compound 1. All hydrogen atoms
regeneration of compound 1 were performed on Perkin-Elmer were omitted for clarity.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 17697–17703 | 17699

View Article Online
RSC Advances
Paper
that compound 1 is in a high pure phase. In order to identify the
thermal stability of compound 1, the thermogravimetric anal-
yses (TGA) have been carried from room temperature to 800 ꢀC
(Fig. S4†). The results indicate that compound 1 losts its non-
coordinated DMF and H2O molecules in the temperature
range of 20–334 ꢀC. The weight loss of 34.40% is consistent with
calculated one of 34.46%. Then the 3D framework continue to
loss weight at higher temperature. The end product of decom-
position of compound 1 is CuO with weight percentage 13.62%
(calculated: 13.69%).
Fig. 2 (a) The cage constructed by six [Cu2(CO2)4] clusters and six
Stability of compound 1
PBPD2ꢁ ligands. (b) The cage constructed by twelve [Cu2(CO2)4]
clusters and six PBPD2ꢁ ligands. (c) The stacking mode of two cages. To investigate the chemical stability of compound 1, we soaked
the as-synthesized samples in different organic solvents such as
CH3OH, C2H5OH, CH3CN, CH2Cl2, CHCl3 for more than two
months. And then to investigate the thermal stability, the as-
˚
of ca. 14.9 ꢂ 32.1 A (Fig. 2b). These two cages are arranged
alternatively to form a cage-stacked 3D framework (Fig. 2c).
synthesized samples were calcined at different temperature of
Topology analysis is applied in order to better understand
the structure of compound 1. If the T-shaped PBPD2ꢁ ligand
serve as a 3-connected node (Fig. 3a) and the paddle-wheel
cluster serve as a 6-connected octahedral node (Fig. 3b), the
resulting structure of compound 1 could be simplied as
ꢀ
ꢀ
ꢀ
150 C, 200 C, and 250 C for 30 min. As shown in Fig. 4, the
PXRD pattern of compound 1 treated in different conditions
matched the simulated X-ray pattern derived from the single
crystal structure, which conrming the structure was not
destroyed when soaked in different solvents and calcined in
variable temperature. These results indicate that compound 1
possesses high thermal stability. We speculate that the high
stability of compound 1 due to the strong energy of the coordi-
nation bond based on the Hard-So-Acid-Base theory (HSAB), the
so-acid metal cations Cu2+ coordinated with so-base N donor of
H2PBPD ligand, forming a much stronger Cu–N bonds. This is the
reason why the compound 1 can keep its structure when soaked in
different solvents, calcined at high temperature and expose in the
air for several months. The HSAB coordination theory maybe an
effective strategy for rationally design and synthesize stable MOFs.
a
(3,6)-connected net (Fig. 3c) with the point symbol
{42$6}2{44$62$86$103}, as calculated by Topos 4.0.
PXRD and thermal analyses of compound 1
The powder X-ray diffraction (PXRD) shows good correlation
between the simulated pattern from the sing-crystal data and
the as-synthesized pattern of compound 1 (Fig. S2†), indicating
Gas sorption properties
N2 adsorption. To investigate the permanent porosity of
compound 1, the N2 adsorption experiments were performed at
Fig. 3 (a) The simplified 3-connected node of the ligand. (b) The
simplified 6-connected node of the binuclear unit [Cu2(COO)4N2].
(c) The (3,6)-connected topological with the symbol of Fig. 4 The PXRD patterns for compound 1 soaked in different solvents
{42$6}2{44$62$86$103} in compound 1.
and heat in variable temperature.
17700 | RSC Adv., 2017, 7, 17697–17703
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
77 K. The as-synthesized compound 1 was activated and
measured by the adsorption analyze. As shown in Fig. 5, the N2
adsorption experiments reveals that compound 1 exhibits
a typical type-I adsorption isotherm, which is characteristic of
microporous materials. The N2 adsorption shows good revers-
ibility. Compound 1 has a total pore volume of 0.70 cm3 gꢁ1
calculated from the N2 isotherm data. The Brunauer–Emmett–
Teller (SBET) and Langmuir surface areas (SLangmuir) are 1682 m2
gꢁ1 and 1992 m2 gꢁ1, respectively. Under the temperature, the
uptake of N2 was 458 cm3 gꢁ1 at 1.0 atm. The pore size distri-
bution shows that compound 1 possesses three types of pore
sizes centered at 0.68 nm, 0.80 nm and 1.00 nm (nonlocal
density functional theory method).
CO2/CH4 adsorption. In addition, low-pressure CO2 and CH4
sorption experiments for compound 1 were measured (Fig. 6).
The sorption isotherms for CO2 reveal that compound 1 can
absorb CO2 up to 114 cm3 gꢁ1 (5.08 mmol gꢁ1 or 22.47 wt%) at
273 K and 1.0 atm, and 83 cm3 gꢁ1 (3.70 mmol gꢁ1 or 16.43 wt%)
at 298 K and 1.0 atm. The uptake amount of compound 1 is
much higher than some of well-known MOFs, such as MOF-5
(6.2 wt%, at 273 K and 1 atm), SUN-4 (20.6 wt%, at 273 K and
1 atm), SUN-21 (18.4 wt%, at 273 K and 1 atm), MOF-602 (5 wt%,
at 273 K and 1 atm),17 However, compound 1 can adsorb 45 cm3
gꢁ1 of CH4 at 273 K and 1 atm, and 22 cm3 gꢁ1 of CH4 at 298 K
and 1 atm, which is much lower than the uptake of CO2. To
predict the selectivity of CO2 versus CH4, we used the ideal
adsorbed solution theory (IAST) to calculate the multi-
component adsorption behavior from the experimental pure-
gas isotherms. The adsorption selectivity for CO2–CH4
mixtures as a function of pressure is presented in Fig. S6.† The
selectivity of CO2 over CH4 reaches a maximum of 6.1 at 298 K
and 1.0 bar, indicating that compound 1 exhibits selectivity to
CO2 over CH4. We speculate that compound 1 can selectively
adsorb CO2 over CH4 because CO2 has a large quadrupole
moment whereas CH4 has none.
Fig. 6 CO2 and CH4 adsorption isotherm of compound 1 at 273 K and
298 K.
Fig. 7 CO2 adsorption/desorption cycles obtained for the compound
1 from 25 to 80 ꢀC.
To better understand the observations and evaluate the
extent of CO2–framework interactions, the Qst for CO2 at low
coverage are calculated by tting the gas adsorption isotherms
at 273 K and 298 K to the Virial equation. The values are 9.5 kJ
molꢁ1 for CO2 (Fig. S7†). This low Qst value shows that the
interactions between CO2 and the framework of compound 1 is
weak. The reason maybe because the open metal sites of paddle-
wheel [Cu2(CO2)4] are occupied by the pyridin of PBPD2ꢁ ligand.
Then we explored the CO2 cyclic adsorption and regenera-
tion of the activated sample under ambient pressure from 25 to
80 ꢀC. As shown in Fig. 7, compound 1 shows a stable CO2
adsorption capacity and no obvious weight change even aer
more than 10 cycles. Then the PXRD of the sample aer CO2
adsorption/desorption cycles was measured, as shown in
Fig. S2,† the structure of compound 1 was still not destroyed,
which also conrmed the stability of the framework.
Conclusions
In summary, a metal–organic framework assembled from T-
shaped pyridyl dicarboxylate ligand 40-(pyridin-4-yl)-[1,10-
Fig. 5 N2 adsorption and desorption isotherms at 77 K. Inset: pore size
distribution of compound 1.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 17697–17703 | 17701

View Article Online
RSC Advances
Paper
biphenyl]-3,5-dicarboxylic acid (H2PBPD) have been success-
fully synthesized via solvothermal reaction with copper(II)
nitrate. Structural analyses revealed that compound 1 is
a three-dimensional framework with (3,6)-connected topology.
Compound 1 exhibits high stability at high temperature and in
organic solvents. In addition, the gas adsorption properties of
compound 1 were investigated, N2 adsorption and desorption
isotherms at 77 K indicated that it is microporous materials and
with high BET surface area of 1682 m2 gꢁ1. And it also exhibit
outstanding adsorption capacity for CO2 and CH4. It is worth
noting that the activated compound 1 exhibits selectivity of CO2
over CH4 at 298 K and 1 bar, indicating that the materials
possesses great potential in CO2 capture and CO2/CH4 separa-
tion. The CO2 cyclic adsorption and regeneration experiments
shows that it has a stable CO2 adsorption capacity and no
obvious weight change aer ten times. These researches reveal
that T-shaped pyridyl dicarboxylate ligand has potential appli-
cations in building MOFs with high stability and high adsorp-
tion capacity.
O. M. Yaghi, J. Am. Chem. Soc., 2000, 122, 1391; (d) J. R. Li,
Y. Tao, Q. Yu, X. H. Bu, H. Sakamoto and S. Kitagawa,
Chem.–Eur. J., 2008, 14, 2771.
5 (a) S. C. Xiang, W. Zhou, J. M. Gallegos, Y. Liu and
B. L. Chen, J. Am. Chem. Soc., 2009, 131, 12415; (b) X. Lin,
I. Telepeni, A. J. Blake, A. Dailly, C. M. Brown,
J. M. Simmons, M. Zoppi, G. S. Walker, K. M. Thomas,
T. J. Mays, P. Hubberstey, N. R. Champness and
¨
M. Schroder, J. Am. Chem. Soc., 2009, 131, 2159; (c)
J. K. Sun, M. Ji, C. Chen, W. G. Wang, P. Wang,
R. P. Chen and J. Zhang, Chem. Commun., 2013, 49, 1624;
(d) Z. X. Chen, S. C. Xiang, H. D. Arman, P. Li, S. Tidrow,
D. Y. Zhao and B. L. Chen, Eur. J. Inorg. Chem., 2010,
3745; (e) Z. Y. Guo, H. Wu, G. Srinivas, Y. M. Zhou,
S. C. Xiang, Z. X. Chen, Y. T. Yang, W. Zhou, M. O'Keeffe
and B. L. Chen, Angew. Chem., Int. Ed., 2011, 50, 3178; (f)
Y.-G. Lee, H. R. Moon, Y. E. Cheon and M. P. k. Suh,
¨
Angew. Chem., Int. Ed., 2008, 47, 7741; (g) D. Lassig,
J. Lincke, J. Moellmer, C. Reichenbach, A. Moeller,
¨
R. Glaser, G. Kalies, K. A. Cychosz, M. Thommes,
R. Staudt and H. Krautscheid, Angew. Chem., Int. Ed.,
2011, 50, 10344; (h) X.-J. Wang, P.-Z. Li, Y. F. Chen,
Q. Zhang, H. C. Zhang, X. Xiang Chan, R. Ganguly,
Y. X. Li, J. W. Jiang and Y. l. Zhao, Sci. Rep., 2013, 3, 1149.
6 (a) I. Spanopoulos, P. Xydias, C. D. Malliakas and
P. N. Trikalitis, Inorg. Chem., 2013, 52, 855; (b) Z. H. Xiang,
C. Q. Fang, S. H. Leng and D. P. Cao, J. Mater. Chem. A,
2014, 2, 7662; (c) B. L. Chen, L. B. Wang, Y. Q. Xiao,
F. R. Fronczek, M. Xue, Y. J. Cui and G. D. Qian, Angew.
Chem., Int. Ed., 2009, 48, 500; (d) Z. M. Hao, X. Z. Song,
M. Zhu, X. Meng, S. N. Zhao, S. Q. Su, W. T. Yang,
S. Y. Song and H. J. Zhang, J. Mater. Chem. A, 2013, 1,
11043; (e) T. Pham, K. A. Forrest, P. Nugent,
Y. Belmabkhout, R. Luebke, M. Eddaoudi, M. J. Zaworotko
and B. Space, J. Phys. Chem. C, 2013, 117, 9340; (f) H. Liu,
Y. G. Zhao, Z. J. Zhang, N. Nijem, Y. J. Chabal, H. P. Zeng
and J. Li, Adv. Funct. Mater., 2011, 21, 4754; (g) H. Liu,
Y. G. Zhao, Z. J. Zhang, N. Nijem, Y. J. Chabal, X. F. Peng,
H. P. Zeng and J. Li, Chem.–Asian J., 2013, 8, 778.
Acknowledgements
We thank the National Natural Science Foundation of China
(Grants: 21471064, 21641004 and 21621001) for support to this
work.
Notes and references
1 (a) P. K. Thallapally, J. Tian, M. R. Kishan, C. A. Fernandez,
S. J. Dalgarno, P. B. McGrail, J. E. Warren and J. L. Atwood,
J. Am. Chem. Soc., 2008, 130, 16842; (b) M. P. Suh,
H. J. Park, T. K. Prasad and D.-W. Lim, Chem. Rev., 2012,
112, 782; (c) T. Remy, G. V. Baron and J. F. M. Denayer,
Langmuir, 2011, 27, 13064; (d) P. Horcajada, C. Serre,
G. Maurin, N. A. Ramsahye, F. Balas, M. Vallet-RegI,
M. Sebban, F. Taulelle and G. Ferey, J. Am. Chem. Soc.,
2008, 130, 6774; (e) J. Y. Lee, O. K. Farha, J. Roberts,
K. A. Scheidt, S. B. T. Nguyen and J. T. Hupp, Chem. Soc.
Rev., 2009, 38, 1450; (f) G. Ferey and C. Serre, Chem. Soc.
´
´
´
Rev., 2009, 38, 1380; (g) C. Wang, D. Liu and W. B. Lin, J.
Am. Chem. Soc., 2013, 135, 13222; (h) L. E. Kreno, K. Leong,
O. K. Farha, M. Allendorf, R. P. V. Duyne and J. T. Hupp,
Chem. Rev., 2012, 112, 1105.
7 (a) Q. P. Lin, T. Wu, S. T. Zheng, X. H. Bu and P. Y. Feng, J.
Am. Chem. Soc., 2012, 134, 784; (b) J. B. Lin, J. P. Zhang
and X. M. Chen, J. Am. Chem. Soc., 2010, 132, 6654; (c)
J. An, S. J. Geib and N. L. Rosi, J. Am. Chem. Soc., 2010,
¨
2 (a) J. R. Li, R. J. Kuppler and H. C. Zhou, Chem. Soc. Rev.,
2009, 38, 1477; (b) J. R. Li, J. Sculley and H. C. Zhou, Chem.
Rev., 2012, 112, 869; (c) K. Sumida, D. L. Rogow,
J. A. Mason, T. M. McDonald, E. D. Bloch, Z. R. Herm,
T. H. Bae and J. R. Long, Chem. Rev., 2012, 112, 724.
3 (a) P. Verma, X. F. Xu and D. G. Truhlar, J. Phys. Chem. C,
2013, 117, 12648; (b) H. M. Cheng, Q. H. Yang and C. Liu,
Carbon, 2001, 39, 1447; (c) C. E. Holland, S. A. Al-Muhtaseb
and J. A. Ritter, Ind. Eng. Chem. Res., 2001, 40, 338; (d)
Z. J. Zhang, Z. Z. Yao, S. C. Xiang and B. L. Chen, Energy
Environ. Sci., 2014, 7, 2868.
132, 38; (d) R. Dawson, E. Stockel, J. R. Holst, D. J. Adams
and A. I. Cooper, Energy Environ. Sci., 2011, 4, 4239.
8 (a) X. L. Zhao and W. Y. Sun, CrystEngComm, 2014, 16, 3247;
(b) B. Y. Li, Z. J. Zhang, Y. Li, K. X. Yao, Y. H. Zhu, Z. Y. Deng,
F. Yang, X. J. Zhou, G. H. Li, H. H. Wu, N. Nijem, Y. J. Chabal,
Z. P. Lai, Y. Han, Z. Shi, S. H. Feng and J. Li, Angew. Chem.,
Int. Ed., 2012, 51, 1412; (c) B. S. Zheng, J. F. Bai, J. G. Duan,
L. Wojtas and M. J. Zaworotko, J. Am. Chem. Soc., 2011,
133, 748; (d) W. Morris, C. J. Doonan, H. Furukawa,
R. Banerjee and O. M. Yaghi, J. Am. Chem. Soc., 2008, 130,
12626; (e) S. Kitagawa, R. Kitaura and S. Noro, Angew.
Chem., Int. Ed., 2004, 43, 2334; (f) C. Janiak, Dalton Trans.,
2003, 2781; (g) S. Kitagawa and R. Matsuda, Coord. Chem.
Rev., 2007, 251, 2490.
4 (a) H. Li, M. Eddaoudi, M. O'Keeffe and O. M. Yaghi, Nature,
1999, 402, 276; (b) N. Li, J. Xu, R. Feng, T. L. Hu and X. H. Bu,
Chem. Commun., 2016, 52, 8501; (c) M. Eddaoudi, H. Li and
17702 | RSC Adv., 2017, 7, 17697–17703
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
9 (a) R. R. Yun, J. G. Duan, J. F. Bai and Y. Z. Li, Cryst. Growth 12 SAINT, version 6.02a, Bruker AXS Inc., Madison, WI, USA,
Des., 2013, 13, 24; (b) S. L. Xiang, J. Huang, L. Li, J. Y. Zhang, 2000.
L. Jiang, X. J. Kuang and C. Y. Su, Inorg. Chem., 2011, 50, 13 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
1743; (c) V. Chandrasekhar, C. Mohapatra and R. K. Metre, 2008, 64, 112.
Cryst. Growth Des., 2013, 13, 4607; (d) M. S. Chen, Z. S. Bai, 14 A. L. Speak, J. Appl. Crystallogr., 2003, 36, 7.
T. Okamura, Z. Su, S. S. Chen, W. Y. Sun and N. Ueyama, 15 J. H. Chen, L. S. Loo and K. Wang, J. Chem. Eng. Data, 2011,
CrystEngComm, 2010, 12, 1935; (e) L. T. Du, Z. Y. Lu,
56, 1209.
K. Y. Zheng, J. Y. Wang, X. Zheng, Y. Pan, X. Z. You and 16 (a) A. Karmakar, L. M. D. R. S. Martins, S. Hazra,
J. F. Bai, J. Am. Chem. Soc., 2013, 135, 562; (f) L. Qin,
J. S. Hu, L. F. Huang, Y. Z. Li, Z. J. Guo and H. G. Zheng,
Cryst. Growth Des., 2010, 10, 4176; (g) Y. L. Hu, M. L. Ding,
X. Q. Liu, L. B. Sun and H. L. Jiang, Chem. Commun., 2016,
52, 5734.
M. F. C. G. Silva and A. J. L. Pombeiro, Cryst. Growth Des.,
2016, 16, 1837; (b) Y. Xiong, Y. Z. Fan, R. Yang, S. Chen,
M. Pan, J. J. Jiang and C. Y. Su, Chem. Commun., 2014, 50,
14631.
17 (a) K. S. Walton, A. R. Millward, D. Dubbeldam, H. Frost,
J. J. Low, O. M. Yaghi and R. Q. Snurr, J. Am. Chem. Soc.,
2008, 130, 406; (b) Y. G. Lee, H. R. Moon, Y. E. Cheon and
M. P. Suh, Angew. Chem., Int. Ed., 2008, 47, 7855; (c)
T. K. Kim and M. P. Suh, Chem. Commun., 2011, 47, 4258;
(d) H. Furukawa, J. Kim, N. W. Ockwig, M. O'Keeffe and
O. M. Yaghi, J. Am. Chem. Soc., 2008, 130, 11650.
10 Q. Wang, X. H. Song, M. X. Zhang, W. L. Liu and J. F. Bai,
Cryst. Growth Des., 2016, 16, 6156.
11 (a) V. A. Blatov, Struct. Chem., 2012, 23, 955; (b)
E. V. Alexandrow, V. A. Blatov, A. V. Kochetkov and
D. M. Proserpio, CrystEngComm, 2011, 13, 3947.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 17697–17703 | 17703