COMMUNICATION
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Element–organic frameworks with high permanent porosityw
a
b
a
a
Marcus Rose, Winfried Bohlmann, Michal Sabo and Stefan Kaskel*
¨
Received (in Cambridge, UK) 10th December 2007, Accepted 25th February 2008
First published as an Advance Article on the web 26th March 2008
DOI: 10.1039/b718925g
Microporous hydrophobic polysilanes with high specific surface
ꢀ1
tallic polymer synthesis route. In the following, we report the
integration of elements such as silicon and their use as
connectors. At the same time, organic linkers are used
to tailor the pore size, resulting in a porous, highly hydro-
phobic and thermally stable element organic framework
(EOF).
2
areas (700–1100 m g ) for applications in gas adsorption are
obtained using an organolithiation route.
The search for novel porous materials with narrow pore size
distribution, high accessible surface area and well defined
functional groups on the inner surface is crucial for the
development of applications in adsorption, separation, gas
storage, and heterogeneous catalysis. A rational design was
achieved in metal–organic frameworks (MOFs), coordination
polymers consisting of connectors (metal ions or clusters) and
linkers (organic molecules with functional groups) defining the
Tetrakis(4-bromophenyl)silane (TBPS), was used as the
primary building block. The synthesis of TBPS was reported
1
7
earlier by Fournier et al. TBPS was lithiated fourfold by
reaction with n-butyllithium under inert conditions. Subse-
quent reaction with tetraethylorthosilicate (TEOS) at 263 K
resulted in the formation of the porous network poly(1,4-
phenylene)silane (EOF-1, Scheme 1). The white product is
separated from the solution by centrifugation. EOF-1 forms as
an X-ray amorphous precipitate composed of very small
1
–4
network topology and pore diameter
and in covalent
organic frameworks (COFs) as an extension of the modular
5
,6
concept using boronic acids as building blocks. They sur-
pass traditional molecular sieves such as zeolites and activated
carbons in terms of surface area and specific pore volume. A
disadvantage of these materials is the low hydrothermal
particles. Instead of TEOS, SiCl can be used for the frame-
4
work formation but the specific surface area is slightly re-
duced. A biphenylene linker was used to obtain larger pores in
7
0
0
stability in some cases. Metals such as chromium in
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MIL-101 have a high toxicity. Other porous organic–inor-
poly(4,4 -biphenylene)silane (EOF-2). Since 4,4 -dibromobi-
phenylene can be lithiated twofold, EOF-2 can be synthesized
in a one-step reaction (Scheme 1), thus the synthesis of the
tetrahedral precursor tetrakis(4-bromobiphenylene)silane is
unnecessary.
ganic hybrid materials of great interest obtained in the last
9
years are the periodic mesoporous organosilicas (PMOs) and
1
0
porous polymers. Hypercrosslinked polymers (HCPs) were
obtained by hypercrosslinking of polymer chains in a swollen
The particle size and the morphology of the resulting
particles was characterized by SEM analysis (Fig. 1). EOF-1
consists of spherical particles with a diameter of 0.1–0.5 mm
while EOF-2 forms a dendritic network of flat particles.
1
1–13
polymer to generate a rigid, porous polymer network.
Another approach is the polymerization of large rigid mole-
cules to form chains and networks with inefficient space
packing and voids in the range of micropores, realized in the
Both polymers are X-ray amorphous. The para-substituted
13
phenylene group (EOF-1) is detected in the C CP MAS
1
4,15
polymers of intrinsic microporosity (PIMs).
Recently
Cooper et al. published the synthesis of conjugated micropor-
NMR spectrum (d = 131.7, 124.1 ppm). A shoulder at
ous polymers (CMPs) using Sonogashira–Hagihara coupling
1
39.5 ppm indicates the presence of non-symmetric substituted
1
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of alkynes with aryl halogens. They showed that the pore size
of the obtained amorphous microporous polymers depends on
the size of the organic linker.
linkers due to incomplete conversion of Ph–Br groups. In the
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Si MAS NMR spectrum one sharp peak at ꢀ17.9 ppm
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reflects the majority of SiPh -groups but a broader region
Our interest was to develop a new class of microporous
materials (d o 2 nm) with high hydrophobicity, high stability
against water and good thermal stability using the
modular concept of connectors and linkers but an organome-
at ꢀ33 to ꢀ43 ppm indicates the presence of some aliphatic
substitution of Si atoms (see supporting information). EOF-1
and EOF-2 have a good thermal stability in air up to 673 K. A
complete degradation is only observed above 873 K.
They show no decomposition by air, moisture, or aqueous
solutions.
a
Department of Inorganic Chemistry, Dresden University of
Technology, Mommsenstr. 6, D-01069 Dresden, Germany.
E-mail: stefan.kaskel@chemie.tu-dresden.de; Fax: +49-351-
Both compounds are highly porous. From the nitrogen
physisorption isotherms measured at 77 K (Fig. 2), the specific
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6337287; Tel: +49-351-46334885
b
Faculty of Physics and Earth Science, University of Leipzig,
Linne´str. 5, D-04103 Leipzig, Germany.
2
surface areas determined using the BET equation are 780 m
ꢀ1
ꢀ1
2
g
(EOF-1) and 1046 m
g
(EOF-2). Using the t-plot
E-mail: bohlmann@physik.uni-leipzig.de; Fax: +43-341-9732769;
Tel: +49-341-9732613
method, a specific micropore volume is determined for
w Electronic supplementary information (ESI) available: Experimental
procedures, NMR, IR and Raman spectra, DTA/TG diagrams and H
and CH physisorption isotherms for EOF-1 and EOF-2. See DOI:
0.1039/b718925g
3
ꢀ1
3
EOF-1 with 0.32 cm g and for EOF-2 with 0.45 cm g
ꢀ1
.
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The external specific surface area is high for both compounds
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(167 m g (EOF-1) and 201 m g (EOF-2)).
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462 | Chem. Commun., 2008, 2462–2464
This journal is ꢁc The Royal Society of Chemistry 2008
Rose, Marcus
