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37.7 kJmolꢀ1). DFT calculations further describe the ꢀNH2···CO2
and CO2···CO2 cooperative interactions in the framework. The
importance of the ꢀNH2 group towards CO2 capture was fur-
ther realized through a postsynthetic modification of ꢀNH2 to
ꢀNHCOCH3. This modification drastically reduces the uptake of
CO2 and also the binding energy. Compound 2 also acts as
a very efficient base catalyst for a Knoevenagel condensation
reaction and shows size selectivity. The present study is signifi-
cant because it displays an elegant example of structural
supramolecular isomerism with multifunctional properties,
such as selective CO2 uptake and catalysis.
C17H19CdN4O6: C 41.86, H 3.92, N 11.48; found: C 42.11, H 4.17, N
11.01.
Synthesis of 2a
Activated (desolvated) 2 (2’; ꢁ50 mg) was stirred with a solution
of acetic anhydride (5 mL) in chloroform (0.5 mmol) for 6–7 d at rt.
Compound 2a was filtered and washed several times with CHCl3,
then dried in air. Compound 2a was characterized by PXRD and
1H NMR spectroscopy (Figure 9b; Figure S12 in the Supporting In-
formation). FTIR (KBr pellet): n˜ =3498 (br), 3240 (w), 3091 (w), 2329
(s), 2241 (m), 2133 (m), 1615 (s), 1569 (s), 1507 (s), 1425 (s), 1311
(w), 1232 (s), 1069 (s), 1021 (s), 915 (w), 877 (w), 831 cmꢀ1 (s); ele-
mental analysis calcd (%) for C16.8H12.8CdN4O4.9: C 36.41, H 2.31, N
10.11; found: C 37.51, H 3.01, N 10.51.
Experimental Section
X-ray crystallography
Materials
X-ray single-crystal structural data of 1 and 2 were collected with
a Bruker Smart-CCD diffractometer equipped with a normal focus,
2.4 kW sealed-tube X-ray source with graphite monochromated
MoKa radiation (l=0.71073 ꢁ), operating at 50 kV and 30 mA. The
program SAINT[25] was used for integration of diffraction profiles
and absorption correction was made with the SADABS[26] program.
All the structures were solved by SIR 92[27] and refined by the full-
matrix least-squares method by using SHELXL-97.[28] All the hydro-
gen atoms were fixed by HFIX and placed in ideal positions. Due
to the weakly diffracting nature of the single crystals we could not
locate the guest molecules and carried out 1H NMR and IR spec-
troscopy and TGA and elemental analysis to confirm the presence
of guest molecules. Potential solvent-accessible areas or void space
was calculated by using the PLATON multipurpose crystallographic
software.[17] All crystallographic and structure-refinement data for
1 and 2 are summarized in Table 1. Selected bond lengths and
angles for 1 and 2 are given in Tables S1 and S2 (see the Support-
ing Information), respectively. All calculations were carried out by
using PLATON and the WinGX system, Ver 1.70.01.[29] CCDC-941967
(1) and 941968 (2) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
data_request/cif.
All the reagents employed were commercially available and used
as provided without further purification. [Cd(NO3)2·6H2O] was ob-
tained from Spectrochem. 2-Aminobenzenedicarboxylic acid, acetic
anhydride, malononitrile, methyl cyanoacetate, p-nitro- and p-
chloro-benzaldehyde were obtained from Sigma Aldrich. 1,2-Bis-(4-
pyridylmethylene)hydrazine was synthesized by
method.[24]
a
literature
Physical measurements
Elemental analysis was carried out with a Thermo Fischer Flash
2000 Elemental Analyzer. IR spectra were recorded as KBr pellets
with a Bruker IFS 66v/S spectrophotometer in the region n˜ =4000–
400 cmꢀ1. TGA was carried with on a Metler Toledo instrument
under a nitrogen atmosphere (flow rate=50 mLminꢀ1) in the tem-
perature range 30–5008C (heating rate=38Cminꢀ1). PXRD patterns
of 1 and 2 were recorded with a Bruker D8 Discover instrument
1
(40 kV, 30 mA) by using CuKa radiation. H NMR spectra were mea-
sured on a Bruker AV-400 spectrometer with chemical shifts report-
ed as ppm (in DCl/[D6]DMSO or CDCl3/CD3CN; TMS as internal stan-
dard).
Synthesis of 1 and 2
Adsorption study
[Cd(NO3)2·6H2O] (0.2 mmol, 0.049 g) was added to a solution of
NH2ꢀbdc (0.2 mmol, 0.035 g) and bphz (0.2 mmol, 0.042 g) in DMF
(14 mL) and the mixture was sonicated for 10–15 min. This solution
was then equally divided into two glass vials; one was kept at
908C and one at 1208C, for 24 h. After cooling to rt, rectangular
block-shaped yellow crystals were found at the walls of the vials.
We obtained 1 from the reaction at 908C and 2 from the reaction
at 1208C. Crystals were separated from the solution and then thor-
oughly washed with DMF. Crystals of both compounds were found
to be weakly diffracting and, hence, for further characterization we
used 1H NMR spectroscopy, elemental analysis, and TGA.
The adsorption isotherms of CO2, H2, N2, Ar, and O2 (T=195 K) mea-
sured from the dehydrated samples of 1 (1’), 2 (2’), and 2a were
measured with a QUANTACHROME QUADRASORB-SI analyzer. The
adsorbent sample (100–150 mg), which had been prepared at
453 K under a 1ꢂ10ꢀ1 Pa vacuum for about 6 h prior to measure-
ment of the isotherms, was placed in the sample tube. Helium gas
(99.999% purity) at a known pressure was introduced into the gas
chamber and allowed to diffuse into the sample chamber by open-
ing the valve. The amount of gas adsorbed was calculated readily
from the pressure difference (PcalꢀPe); Pcal is the calculated pressure
with no gas adsorption, Pe is the observed equilibrium pressure. All
operations were computer controlled and automatic.
Compound 1: Yield: 67%, relative to Cd. FTIR (KBr pellet): n˜ =3490
(br), 3234 (w), 3072 (w), 2326 (s), 2238 (m), 2128 (m), 1614 (s), 1562
(s), 1502 (s), 1428 (s), 1310 (w), 1228 (s), 1068 (s), 1020 (s), 912 (w),
874 (w), 820 cmꢀ1 (s); elemental analysis calcd (%) for
C17H19CdN4O6: C 41.86, H 3.92, N 11.48; found: C 41.21, H 4.41, N
10.97.
Computational details
All periodic calculations were carried out by DFT as implemented
in the QUICKSTEP module in CP2K.[30] A mixed basis set was used,
in which Kohn–Sham orbitals were expanded in an atom-centered
Gaussian basis set and electronic charge density was described by
using an auxiliary-plane wave basis set. Initial coordinates were
Compound 2: Yield: 58%, relative to Cd. FTIR (KBr pellet): n˜ =3490
(br), 3234 (w), 3072 (w), 2326 (s), 2238 (m), 2128 (m), 1614 (s), 1562
(s), 1502 (s), 1428 (s), 1310 (w), 1228 (s), 1068 (s), 1020 (s), 912 (w),
874 (w), 820 cmꢀ1 (s); elemental analysis calcd (%) for
Chem. Eur. J. 2014, 20, 4347 – 4356
4354
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