From a supramolecular tetranitrile to a porous covalent triazine-based framework with high gas uptake capacities

Article abstract of DOI:10.1039/c3cc41382a

Transformation of tetra(4-cyanophenyl)ethylene under Lewis acidic (ZnCl₂) conditions at 400 °C leads to the formation of a porous covalent triazine-based organic framework (CTF) with a high surface area (2235 m² g^-1), high

Full text of DOI:10.1039/c3cc41382a

ChemComm
View Article Online
View Journal
COMMUNICATION
From a supramolecular tetranitrile to a porous
covalent triazine-based framework with high
Cite this: DOI: 10.1039/c3cc41382a
gas uptake capacities†‡
Received 22nd February 2013,
Accepted 26th March 2013
Asamanjoy Bhunia, Vera Vasylyeva and Christoph Janiak*
DOI: 10.1039/c3cc41382a
www.rsc.org/chemcomm
Transformation of tetra(4-cyanophenyl)ethylene under Lewis acidic (terephthalonitrile) have provided high surface areas (over
2
ꢀ1
(
ZnCl
2
) conditions at 400 8C leads to the formation of a porous 3000 m g ) only at high temperatures, i.e., heating to 400 1C
9
covalent triazine-based organic framework (CTF) with a high surface for 20 h and then to 600 1C for 96 h. Heating to 400 1C gave a
2
ꢀ1
2
ꢀ1 10
area (2235 m
g
), high CO
2
and CH
4
uptakes and the highest lower surface area of only 1710 m g
.
A high surface area CTF
2
ꢀ1
hydrogen uptake for a CTF material (1.86 wt% at 77 K, 1 bar).
of 2390 m g could be obtained by using microwave ionother-
mal conditions, albeit in low yield and in a difficult-to-control
1
1,12
Microporous organic polymers (MOPs) have attracted huge reaction.
Very recently, CTFs with surface areas of up to
2
ꢀ1
attention because of their potential applications in gas storage, 1152 m g were synthesized with strong Brønsted acids, such
1
,2
separation, catalysis and optoelectronics. A variety of MOPs as trifluoromethanesulfonic acid, under both room temperature
with permanent porosity such as benzimidazole-linked polymers and microwave assisted conditions.
Strong Brønsted acid conditions provide lower surface areas
intrinsic microporosity (PIMs), porous aromatic frameworks but they avoid decomposition and condensation reactions such
PAFs), conjugated microporous polymers (CMPs), covalent as C–H bond cleavage and carbonization. In contrast to strong
organic frameworks (COFs), covalent triazine-based organic Brønsted acids, ionothermal conditions offer the significant
frameworks (CTFs) have been prepared by combinations of advantages of cheap, easy handling and yielding materials with
reversible and irreversible organic reactions and with differing high surface areas. Here we have employed the new tetranitrile,
13
2
3
(BILPs), hyper-cross-linked polymers (HCPs), polymers of
4
5
6
14
(
7
8
7a
1
gas uptake capacities. MOPs have advantages, such as high tetra(4-cyanophenyl)ethylene 1 (see ESI‡ for synthesis and char-
stability (around 600 1C), permanent porosity with high specific acterization) to obtain two novel porous covalent triazine-based
surface area and light weight in contrast to metal–organic frame- organic frameworks (PCTFs) identified as PCTF-1 and PCTF-2 by
works (MOFs). MOPs are mainly constructed by light elements using different ratios of ZnCl
through strong covalent bonds (e.g., C–C, C–N, C–O), hence they The solid-state structure of the tetranitrile 1 already shows a
have low densities. These features make these materials attractive 3D supramolecular network organized by p-stacking (Fig. 1)
for applications in which weight reduction is crucial. with potential porosity.§ The material was activated by degassing
Kuhn, Antonietti and Thomas et al. developed CTFs with at 100 1C under high vacuum (10 Torr) for 24 h. While the pores
2
(Scheme 1).
ꢀ
6
8–10
permanent porosity.
In contrast to COFs or other MOPs, CTFs
are interesting because of advantages such as very cheap and readily
available starting materials, easy synthesis and hydrophilicity.
Porous CTF materials can be synthesized by an ionothermal reac-
2
tion between aromatic nitriles and ZnCl which can be adapted to a
large scale. Molten ZnCl acts as a Lewis acid and solvent (porogen)
2
for the polymerization. A trimerization reaction of nitrile groups
can construct triazine rings. To date, CTFs from 1,4-dicyanobenzene
Institut f u¨ r Anorganische Chemie und Strukturchemie, Universit a¨ t D u¨ sseldorf,
4
0204 D u¨ sseldorf, Germany. E-mail: janiak@uni-duesseldorf.de;
Fax: +49-211-81-12287; Tel: +49-211-81-12286
†
‡
Dedicated to Prof. Dr Werner Uhl for his 60th birthday.
Electronic supplementary information (ESI) available: Experimental part, NMR,
IR, TG-MS, XRD, gas uptake and selectivity. CCDC 924716. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c3cc41382a
Scheme 1 Idealized structure of PCTF from the polymerization of 1.
This journal is c The Royal Society of Chemistry 2013
Chem. Commun.

View Article Online
Communication
ChemComm
Fig. 2 Scanning electron micrographs of PCTF-1 (left) and PCTF-2 (right).
Fig. 3
2
N sorption isotherms of PCTF-1 and PCTF-2 at 77 K.
(Table 1) with the type IV isotherm and an associated H2 type
hysteresis, typical for a microporous material with additional
7,9
Fig. 1 Molecular unit (top) and packing diagram (bottom) of the solid-state mesoporosity, possibly formed by close-packed nanoparticles
2
ꢀ1
structure of 1. Solvent molecules in channels along the c direction are not shown. (Fig. 3). PCTF-2 exhibited a surface area of 784 m g . Only a
small degree of hysteresis was observed upon desorption. The
isotherm is of type II with some type IV character, indicating a
material with relatively large pores (Fig. 3). The surface area and
pore volume depend on the amount of ZnCl porogen.
2
were too narrow for N
and CO (77 K and 273 K, respectively) were adsorbed up to
.9 and 7.6 cm g (as found for other organic frameworks),
2
adsorption at 77 K (kinetic hindrance),
H
8
2
2
3
ꢀ1
15
Non-local density functional theory (NLDFT) pore size distribu-
tions using a slit pore model for PCTF-1 and PCTF-2 indicate that a
significant fraction of the pores surface still originates from micro-
pores with a diameter less than 2 Å (Fig. 4, V0.1 in Table 1). Super-
micropores are expected for CTFs between 10 and 20 Å due to the
corresponding to 0.08 and 1.49 wt%, respectively at P/P = 0.95 bar.
0
The aim of the synthesis of CTFs is to obtain high surface areas
at lower temperatures (400 1C) instead of 500–700 1C to reduce
energy and avoid unnecessary decomposition. Here, a mixture of 1
2
and ZnCl in quartz ampoules was heated at 400 1C for 48 h. The
9
triazine system and pore opening of the hexamer. However, this
crude product was stirred in water and diluted HCl for 24–48 h (see
ESI‡). The yield of the frameworks (PCTF-1 and PCTF-2) is around
fraction is much smaller for PCTF-2 than PCTF-1. For PCTF-1 the
additional mesopores are broadly distributed between 20 and 60 Å.
For PCTF-2 the pore size distribution extends from 20 Å to well over
ꢀ
1
9
0%. In FT-IR the intense CN band around 2226 cm disappeared
for both materials, indicating complete reaction of the nitrile
9
100 Å. The level of microporosity was compared by the ratio of micro-
groups (Fig. S6, ESI‡). From TGA it was observed that the PCTFs
pore to total pore volume (V /V , Table 1). V /V B 0.5 and less
indicates the presence and increasing dominance of mesopores.
start to decompose with significant weight loss only above 450 1C
0.1 tot
0.1 tot
16
(Fig. S8, ESI‡). Elemental analysis (Table S1, ESI‡) of these frame-
Most interestingly, PCTF-1 adsorbs 1.86 wt% H at 77 K and
bar (Fig. 5). To the best of our knowledge, this is the highest
works indicate nitrogen elimination during the polymerization
reaction. In TG-MS the formation of CN and HCN was observed
2
1
value reported for any type of CTFs. The polymer from
(Fig. S9, ESI‡). Powder X-ray diffraction of the frameworks con-
firmed their expected amorphous nature. Scanning electron micro-
scopy images illustrate macro- and mesoporosity with the porosity
of PCTF-1 being more homogeneous than that of PCTF-2 (Fig. 2).
Nitrogen sorption studies of PCTF-1 and PCTF-2 at 77 K (Fig. 3) Comp
Table 1 Porosity data for PCTFs from N
2
isotherms at 77 K
a
b
c
S
BET
S
Lang
V
0.1
V
tot
2
ꢀ1
2
ꢀ1
3
ꢀ1
3
ꢀ1
(m g
)
(m g
)
(cm g
)
(cm g
)
V0.1/Vtot
showed a first step at P/P
micropores. The nitrogen uptake at low pressures increases from PCTF-2
0
o 0.05 corresponding to gas sorption in
PCTF-1
2235
784
2777
1313
0.79
0.29
1.56
0.76
0.51
0.38
PCTF-1 to PCTF-2 concomitantly with a gain in the overall surface
area. PCTF-1 provided a remarkable surface area of 2235 m g
a
b
0
Calculated BET surface area over the pressure range 0.01–0.05 P/P .
Pore volume at P/P = 0.1. Total pore volume at P/P = 0.95.
0 0
2
ꢀ1
c
Chem. Commun.
This journal is c The Royal Society of Chemistry 2013

View Article Online
ChemComm
Communication
respectively, at 273 K. The selectivity of PCTF-1 or PCTF-2 does not
depend only on the size of the gas components (kinetic diameter:
CO 3.3 Å, N 3.6 Å and CH 3.8 Å) but also on the polarizability of
2
2
4
the surface and of the gas components. Recently, Cooper et al.
calculated CO :N selectivities for various CTFs between 16 and 31
2
2
13
at 273 K using the Ideal Adsorbed Solution Theory (IAST).
In summary, tetranitrile tetra(4-cyanophenyl)ethylene not
only gives a porous supramolecular network but also yields a
porous CTF with a high surface area already at 400 1C under
2
ionothermal conditions. PCTF-1 shows the highest H uptake
capacity (1.86 wt%) for a CTF material. Such a tetranitrile
provides a novel strategy for the development of functional
CTF materials with a high surface area and gas storage capacity.
Fig. 4 NL-DFT pore size distribution curve of PCTF-1 and PCTF-2.
Notes and references
ꢀ
1
§
Crystal data for 1: C30
16 4 1
H N , M = 432.47 g mol , tetragonal, I4 /acd,
3
a = 22.0767(8) Å, c = 21.1707(10) Å, V = 10318.2(7) Å , Z = 16, m(Cu-Ka) =
ꢀ1
0
.543 mm , T = 173(2) K, 10 909 reflections measured, 753 indepen-
dent (Rint = 0.0295), final R 0.0592 (I > 2s(I)), wR = 0.1693 (all data),
goodness of fit on F = 1.105. CCDC 924716.
1
2
2
1
S.-Y. Ding and W. Wang, Chem. Soc. Rev., 2013, 42, 548–568; Y. Jin, Y. Zhu
and W. Zhang, CrystEngComm, 2013, 15, 1484–1499; Z. Xiang and D. Cao,
J. Mater. Chem. A, 2013, 1, 2691–2718; N. B. McKeown and P. M. Budd,
Macromolecules, 2010, 43, 5163–5176; R. Dawson, A. I. Cooper and D. J.
Adams, Prog. Polym. Sci., 2012, 37, 530–563; J. Germain, J. M. J. Fr ´e chet and
F. Svec, Small, 2009, 5, 1098–1111; P. Kaur, J. T. Hupp and S. T. Nguyen, ACS
Catal., 2011, 1, 819–835; U. H. F. Bunz, Chem. Rev., 2000, 100, 1605–1644.
M. G. Rabbani and H. M. El-Kaderi, Chem. Mater., 2012, 24, 1511–1517.
J. Germain, J. Hradil, J. M. J. Fr ´e chet and F. Svec, Chem. Mater., 2006,
18, 4430–4435.
2
3
Fig. 5
2
H sorption isotherms for PCTF-1 and PCTF-2 at 77 K.
4
5
6
7
B. S. Ghanem, K. J. Msayib, N. B. McKeown, K. D. M. Harris, Z. Pan,
P. M. Budd, A. Butler, J. Selbie, D. Book and A. Walton, Chem.
Commun., 2007, 67–69.
T. Ben, H. Ren, S. Ma, D. Cao, J. Lan, X. Jing, W. Wang, J. Xu,
F. Deng, J. M. Simmons, S. Qiu and G. Zhu, Angew. Chem., Int. Ed.,
2009, 48, 9457–9460.
J.-X. Jiang, F. Su, A. Trewin, C. D. Wood, N. L. Campbell, H. Niu,
C. Dickinson, A. Y. Ganin, M. J. Rosseinsky, Y. Z. Khimyak and
A. I. Cooper, Angew. Chem., Int. Ed., 2007, 46, 8574–8578.
(a) S. Kandambeth, A. Mallick, B. Lukose, M. V. Mane, T. Heine and
R. Banerjee, J. Am. Chem. Soc., 2012, 134, 19524–19527; (b) A. I.
Cooper, CrystEngComm, 2013, 15, 1483; (c) K. S. W. Sing, D. H. Everett,
R. A. W. Haul, L. Moscou, R. A. Pierotti, J. Rouquerol and T. Siemieniewska,
Pure Appl. Chem., 1985, 57, 603–619.
Table 2
2 2 4
H , CO and CH uptakes of PCTF-1 and PCTF-2 at 1 bar
a
b
c
b
c
H
2
CO
2
CO
2
CH
4
CH
4
3
3
ꢀ1
3
ꢀ1
3
ꢀ1
ꢀ1
Comp
(wt%)
(cm g
)
(cm g
)
(cm g
)
(cm g )
PCTF-1
PCTF-2
1.86
0.9
73.0
41.5
44.9
24.2
23.6
15.1
15.2
8.0
a
b
c
H
2
uptake at 77 K. Gas uptake at 273 K. Gas uptake at 293 K.
0
8
4
,4 -biphenyldicarbonitrile adsorbs 1.55 wt% H
2
at 1 bar, 77 K.
uptake capa-
Microwave-obtained ionothermal CTFs showed H
cities ranging from 0.7 to 1.78 wt% at 1 bar and 77 K. At the
same time, PCTF-2 adsorbed 0.9 wt% H at 77 K and 1 bar. The
CO and CH
two different temperatures at 1 bar (Table 2, Fig. S14–S17 in ESI‡).
2
8 P. Kuhn, M. Antonietti and A. Thomas, Angew. Chem., Int. Ed., 2008,
47, 3450–3453.
9
1
1
P. Kuhn, A. l. Forget, D. Su, A. Thomas and M. Antonietti, J. Am.
Chem. Soc., 2008, 130, 13333–13337.
2
2
4
uptake capacities of the PCTFs were measured at 10 P. Kuhn, A. Thomas and M. Antonietti, Macromolecules, 2009, 42, 319–326.
11 W. Zhang, C. Li, Y.-P. Yuan, L.-G. Qiu, A.-J. Xie, Y.-H. Shen and
J.-F. Zhu, J. Mater. Chem., 2010, 20, 6413–6415.
3
ꢀ1
The volume of CO adsorbed on PCTF-1 at 273 K with 73 cm g
lies towards the upper end when compared to other CTFs which
2
12 Several attempts to synthesize CTFs under microwave irradiation at
high temperature were unsuccessful in our hands and led only to
damages of the microwave as well as the crucible in the solid-state
reaction. Under these reaction conditions we also observed only low
yield of the product from 1,4-dicyanobenzene.
3
ꢀ1
13
showed CO
volume of CH
Noteworthily, for CTFs no CH
yet. In line with the smaller surface area and pore volume the gas
uptake capacity of PCTF-2 is roughly half that of PCTF-1.
2
uptakes of 20–93 cm g at 273 K and 1 bar. The
3
ꢀ1
4
adsorbed on PCTF-1 is 23.6 cm g at 273 K.
4
sorption data have been recorded 13 S. Ren, M. J. Bojdys, R. Dawson, A. Laybourn, Y. Z. Khimyak,
D. J. Adams and A. I. Cooper, Adv. Mater., 2012, 24, 2357–2361.
14 I. B. Johns, E. A. McElhill and J. O. Smith, Ind. Eng. Chem. Prod. Res.
Dev., 1962, 1, 277–281.
Moreover, the CO uptake capacity is higher than the CH uptake 15 Y. Jin, B. A. Voss, R. McCaffrey, C. T. Baggett, R. D. Noble and
2
4
W. Zhang, Chem. Sci., 2012, 3, 874–877.
6 R. Dawson, A. Laybourn, R. Clowes, Y. Z. Khimyak, D. J. Adams and
A. I. Cooper, Macromolecules, 2009, 42, 8809–8816.
17 V. Abetz, T. Brinkmann, M. Dijkstra, K. Ebert, D. Fritsch, K. Ohlrogge,
D. Paul, K. V. Peinemann, S. Pereira-Nunes, N. Scharnagl and M. Schossig,
AIChE J., 2006, 8, 328–358.
8 Y.-S. Bae, O. K. Farha, A. M. Spokoyny, C. A. Mirkin, J. T. Hupp and
R. Q. Snurr, Chem. Commun., 2008, 4135–4137.
capacity at 273 K and 293 K at 1 bar, indicating the selectivity of CO2
sorption over CH sorption. The ratio of the initial slopes in the
Henry region of the adsorption isotherms (Fig. S20–S24 in ESI‡)
determines the selectivities exhibited by PCTF-1 and PCTF-2 for
adsorption of CO over N and for CO over CH . PCTF-1 shows
selectivity ratios of 13 : 1 and 5 : 1 for CO :N and CO :CH
1
4
1
7,18
2
2
2
4
1
2
2
2
4
,
This journal is c The Royal Society of Chemistry 2013
Chem. Commun.