2
450
Joana de A. e Silva et al. / Tetrahedron Letters 54 (2013) 2449–2451
the CO
2
sequestering process by the use of elaborated multiporous
aromatic quinoline substituents make an angle of 60.40(2)° and
materials, like zeolites, porous polymers and metal-organic frame-
works, showed significant advances.1 However those materials
present some synthetic difficulties and/or purification issues and
we need to guide our research to the direct use of multiporous
crystalline materials obtained by self-organization during the ther-
mal crystallization, without the use of metal cations as templates.
In the endeavour for the synthesis of efficient ‘all-organic’ mate-
75.62(12)° with the central plane. Such conformation allows for a
–3
i
weak intermolecular interaction, C15–H15ꢁ ꢁ ꢁ
with a distance between the carbon and the
3.685(6) Å.
p
p
, i: x ꢀ 1, y ꢀ 1, z,
electron cloud of
The unit cell contains large accessible voids (18.4% of the total
unit cell volume) which host disordered solvent molecules. The
contribution of these solvent molecules to the scattering power
1
2
rials for CO
2
sequestering, porphyrins are important compounds. In
was suppressed using the SQUEEZE option in PLATON. The inter-
stitial channels are formed parallel to the a axis centred at y = 0,
z = 0.5 and y = 0.5 and z = 0 (Fig. 1). The unit cell contains large
fact porphyrins can crystallize in robust multiporous metal-organic
structures that can be used as catalysts.4 Their crystalline net-
works have the adequate resistance and morphology to be used
as materials for host inclusion and gases sequestering.6
,5
3
accessible voids, with an average volume of 423 Å perfectly ade-
–8
3
quate for CO
2
sequestering, whose volume is approximately 51 Å .
The porphyrins with quinoline motifs appended in the meso
positions seemed to us to have the structural characteristics in
terms of large crystal channels, in parallel with interesting visible
and fluorescence spectra, and were therefore our first choice for
For the analysis of CO
2
sorption we used an in-house built vol-
1
3
umetric system, where the ratio between the sample chamber
free volume and the reference volume is approximately two. To de-
rive the adsorbed quantities from pressure and temperature data
we used the Benedict–Webb–Rubin equation of state on a dedi-
cated developed software, which includes corrections for pressure
transducer calibration and small temperature variations. The sam-
ple chamber free volume was determined by expanding He gas at
the synthesis of new metal free, ‘all-organic’, crystalline CO
sequestering materials.
2
Experimental section
room temperature (rt) from the calibrated reference volume
3
(
2.925(4) cm ) to the previously evacuated sample chamber. A
All reagents were used as purchased, except for pyrrole that was
sample of TQP dried at 80 °C for 5 h under vacuum (6 mmHg)
was further dried under air at 150 °C for 200 min prior to the
adsorption measurements. The sample dry mass (0.1161 g) was
obtained from the time evolution of the sample mass monitored
on a digital balance after the opening of the drying oven, as it ad-
sorbed atmospheric gases for several minutes.
distillated under reduced pressure, prior to use. The meso-tetrakis-
2
-quinolyl-porphyrin (TQP) (1 in Scheme 1) and meso-tetraphenyl-
porphyrin (TPP) (2 in Scheme 1) were synthesized by adapting the
9–11
Rothemund/Adler/Long methodology
tetrakis-porphyrins.
for the synthesis of meso-
The X-ray data were collected on a Bruker APEX II single crystal
diffractometer, at 298(3) K, using monochromatic Mo K radiation
k = 0.7107 Å). The unit cell dimensions are a = 6.7187(3) Å;
b = 13.4101(7) Å; c = 26.0880(15) Å, b = 92.377(3)° with V =
A new drying process was performed in the volumetric system
at 150 °C for two hours in dynamical vacuum prior to the determi-
a
(
nation, at room temperature, of the sample chamber free volume of
3
3
6
.056(9) cm . We acquired then adsorption/desorption 20 °C iso-
2
348.5(2) Å and space group P2
1
/c. The crystal data of TQP contain
ꢀ
3
therm sequences by successive cumulative CO
the reference volume at increasing equilibrium pressures up to
around 5 bar and then back to lower pressures by releasing CO
2
expansions from
two molecules in the unit cell.
q
calc = 1.158 gcm , Z = 2,
l =
ꢀ
1
0
.070 mm
.
R
(I > 2r
(I)) = 0.0967 and = 0.2561 for 4453
R
w
independent reflections. H atoms were placed at calculated posi-
tions and refined as riding on their parent atoms. The effect of
the disordered solvent molecules was corrected with the SQUEEZE
program.
2
from the sample chamber to the reference volume. We repeated
the cycle in four successive assays as shown in Figure 2.
At 5 bar we obtain an adsorption capacity of 0.15 mmolCO2
/
mmolTQP. The result is the same for the four cycles within the sen-
sitivity limits of the measurements. These results are compared in
Figure 2 with the adsorption observed at room temperature in
meso-tetra-phenyl-porphyrin (TPP) made and crystallized under
Results and discussion
Despite 5, 10, 15, 20-tetra-(2-quinolyl)-21H, 23H-porphine
2
similar conditions. The CO adsorption in TPP crystals is not clearly
(
meso-tetra-2-quinolyl-porphyrin, TQP) has been described previ-
1
4
ously, never its structure was solved by X-ray single crystal
determination. Our synthetic methodology gave us large purple
crystals that allowed for the first time the structure elucidation
of TQP. The crystal asymmetric unit of this porphyrin comprises
one half of a centrosymmetric substituted porphyrin molecule
_
_
_
_
_
_
TQP assay_a
TQP assay_b
TQP assay_c
TQP assay_d
TPP assay_a
TPP assay_b
0.2
(Fig. 1). The macrocycle framework is roughly planar, no individual
atom is displaced more than 0.07(3) Å from the mean plane. The
R
0.1
0.0
N
1
2
R=
R=
NH
N
N
R
R
HN
0
1
2
3
4
5
P (bar)
R
Figure 2. CO
2
adsorption (closed symbols)/desorption (open symbols) isotherms at
Scheme 1.
20 °C in crystalline TQP and TPP.
Silva, Joana De A. E
