Hydrogen-bonded supramolecular polymers containing dimethylsilane groups: Synthesis, crystal structure, and characterization

Article abstract of DOI:10.1002/pola.26166

Bis[N-(4-carboxyphenyl)phtalimidyl]dimethylsilane prepared by the reaction between bis(3,4-dicarboxyphenyl)dimethylsilane anhydride and p-aminobenzoic acid has been used to built three novel hydrogen-bonded supramolecular polymers as a result of cocrystal

Full text of DOI:10.1002/pola.26166

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Hydrogen-Bonded Supramolecular Polymers Containing Dimethylsilane
Groups: Synthesis, Crystal Structure, and Characterization
Mirela-Fernanda Zaltariov, Maria Cazacu, Sergiu Shova, Angelica Vlad, Iuliana Stoica,
Elena Hamciuc
‘‘Petru Poni’’ Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, Iasi 700487, Romania
Correspondence to: M. Cazacu (E-mail: mcazacu@icmpp.ro)
Received 7 February 2012; accepted 8 May 2012; published online
DOI: 10.1002/pola.26166
ABSTRACT: Bis[N-(4-carboxyphenyl)phtalimidyl]dimethylsilane
prepared by the reaction between bis(3,4-dicarboxyphenyl)di-
methylsilane anhydride and p-aminobenzoic acid has been
used to built three novel hydrogen-bonded supramolecular
polymers as a result of cocrystallization with pyridine deriva-
tives: 4,40-bipyridyl (SP1), 1,2-bis(4-pyridyl)ethylene (SP2), and
4,40-azopyridine (SP3). The structures of the dianhydride,
diacid, and derived supramolecular polymers were investigated
by Fourier transform infrared (FTIR) and proton magnetic reso-
nance (1H NMR) spectroscopy. Self-assembling was proved by
the presence of the IR absorption bands around 1900 and 2400
cmꢀ1 specific for hydrogen bond. The association constant val-
ues were estimated by using FTIR spectroscopy in solid state.
According to X-ray diffraction study, the bis(3,4-dicarboxyphe-
nyl)dimethylsilane anhydride (1) has an isolated molecular
(2) molecules are associated in the crystal structure via dimeric
OAH…O hydrogen bonds resulting in the wavy 1D supramo-
lecular chain. The main packing motif for SP1 and SP3 is repre-
sented by wavy chain formed by alternating sequences of 4,40-
bipyridyl or 4,40-azopyridine and bis[N(4-carboxyphenyl)phtali-
midyl]dimethylsilane molecules linked by OAH…N hydrogen
bonds. Thermal behavior was studied by differential scanning
calorimetry and thermogravimetric analysis. The ability for the
structuration in film was emphasized by atomic force micros-
copy. The molecular transport ability of the reversible associa-
tions was estimated by dynamic water vapor sorption (DVS)
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2012 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 000: 000–000, 2012
KEYWORDS: atomic force microscopy (AFM); self-assembly; sili-
structure.
Bis[N-(4-carboxyphenyl)phtalimidyl]dimethylsilane
con derivative; supramolecular structures; X-ray
INTRODUCTION The direct association of the synthetic
molecules into defined architectures is the area of supra-
molecular chemistry also known as chemistry beyond the
molecule.1 Fundamental forces in this field are noncova-
lent interactions mainly consisting of electrostatic (ion–
ion, ion–dipole, and dipole–dipole) interactions, coordina-
tive (metal–ligand) bonding, hydrogen bonding, and Van
der Waals forces.1–4 One of the most used interactions to
build supramolecular structures is hydrogen bond for
which the presence of the complementary proton acceptor
and donor is necessary.1,5,6 The strength of hydrogen-
bonded complexes depends not only on the number of
hydrogen bonds but also on the arrangement of the donor
and acceptor functional groups. Various structures based
on multiple hydrogen bonds have been synthesized and
investigated.7–10 However, a wide variety of main-chain,
side-chain, combined, and network polymeric complex
structures have also been built based on a single H-bond
between acceptor and donor (i.e., carboxyl and pyridyl
functional groups).11,12
A particularly interesting concept in supramolecular chemis-
try is the supramolecular polymer, also called ‘‘polymeric
complex’’ consisting of an array of low-molecular-weight
molecules linked by directional, noncovalent interactions,
which must be stronger than the interchain interactions to
form linear chains selectively.13 Because these interactions
are weaker than covalent bonds, the supramolecular poly-
mers are thermodynamically less stable, kinetically more la-
bile, and dynamically more flexible than covalent polymers.11
The dynamic flexibility results in two principal properties
exhibited by supramolecular materials, namely, stimuli-
responsiveness and self-assembly of nanostructures, both of
which being difficult to attain by using standard covalent
polymers.14 Because of the dynamic character of the bonds,
supramolecular polymers often show much better solubility
and lower melt viscosity and hence display better process-
ability than classical long-chain thermoplastics.15 Many
diverse applications are envisaged for these kinds of materi-
als, including smart, self-healing, and functional materials,
with integrated dynamic functions such as photo and electric
Additional Supporting Information may be found in the online version of this article.
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properties, chemical transport, molecular sensoring, molecu-
lar information, or catalytic activities.11,16,17–19
nance (1H NMR) spectroscopy and X-ray single-crystal diffrac-
tion. The association constants were estimated on the basis of
FTIR measurements. Thermal behavior was studied by differ-
ential scanning calorimetry (DSC) and thermogravimetric anal-
ysis (TGA). The ability for the structuration in film was
emphasized by atomic force microscopy (AFM), and the mois-
ture behavior was studied by water vapor sorption (DVS)
analysis in dynamic regime.
Organic materials used in modern optoelectronics can be in
the form of polymer films, molecular crystals, or supramolecu-
lar assemblies.20 It has been certainty established that the
supramolecular interactions between organic molecules not
only confer them the ability to self-organize into large regular
assemblies but also enhance their electronic and luminescent
properties, which should help to improve the performance of
the organic devices.21 The use of the self-assembled p-conju-
gated molecules in electronic devices is of high interest for the
scientific community in molecular electronics, for which
obtaining monodomain-ordered structures in the hundreds
nanometers to micrometer range is highly desired to achieve a
control over all length scales and interchain electronic coupling
to occur.22 In single-crystal organic semiconductors, band-like
transport can exist due to the relatively highly ordered struc-
ture and extensive orbital overlap of p-systems.23 Supramolec-
ular chemistry is ideal for obtaining entities of such size range
that is most suitable for electronic applications.
EXPERIMENTAL
Materials
Tetracarboxylic acid, bis(3,4-dicarboxyphenyl)dimethylsilane,
was prepared by a two-step procedure according to a method
described in the literature:31 the reaction of 4-bromo-o-xylene
with dimethyldichlorosilane afforded bis(3,4-dimethylphenyl)-
dimethylsilane, which was further oxidized with aqueous po-
tassium permanganate-pyridine (yield: 9.70 g, 55.8%, m.p. ¼
196–198 ꢁC). The following reactants were used: 4,40-bipyr-
idyl, anhydrous, m.p. ¼ 109–112 ꢁC (Fluka); 1,2-bis(4-pyri-
dyl)ethylene, assay 97%, m.p. ¼ 148–152 ꢁC (Aldrich); 4,40-
ꢁ
azopyridine, m.p. ¼ 96–101 C (Aldrich); p-aminobenzoic acid,
Aromatic poly(imide)s (PIs) are materials of high interest for
microelectronics and optoelectronics owing to their excellent
thermal, mechanical, and electrophysical properties. Therefore,
the design of PIs with tunable optoelectrical properties is a con-
cern of modern polymer chemistry. One of the ways to modify
physical properties of PIs is the incorporation of functional frag-
ments and groups into their macromolecules that can increase
the solubility of the as-modified polymers and also impart hole
transport and electrochromic properties to them.24
m.p. ¼ 187–189 ꢁC (Aldrich); acetic anhydride, b.p. ¼ 139.8
ꢁC, q ¼ 1.082 g/mL (Aldrich); and glacial acetic acid, b.p. ¼
ꢁ
118–119 C, q ¼ 1.049 g/mL (Aldrich). The following solvents
were used: methanol and ethanol (Chimopar S.A.); tetrahydro-
furan and diethyl ether (Aldrich) were used as received.
Analyses
FTIR spectra were recorded using a Bruker Vertex 70 FTIR
spectrometer. Registrations were performed in the transmission
mode in the range of 400–4000 cmꢀ1 at room temperature
with a resolution of 2 cmꢀ1 and accumulation of 32 scans.
In the recent past, we tried to modify a PI by alternating its
segment, 1,3-bis(3-trimellitylimidopropyl)tetramethyldisilox-
ane, with organic one, 4,40-bipyridyl, by noncovalent interac-
tions.25 The resulted compound showed liquid crystal behav-
ior and proved to be effective in gas sensing (CO2 and NOx).26
1
ꢁ
H NMR spectra were acquired in DMSO or acetone at 25 C
with a Bruker Avance DRX 400 MHz spectrometer operating
1
at 400.13 MHz for H. The spectrometer was equipped with a
5-mm four nuclei and direct detection z-gradient probe head.
Chemical shifts are reported in ppm and are referenced to
dimethylsulfoxide (d1H ¼ 2.51 ppm) or acetone (d1H ¼ 2.09).
In this study, we used, as proton donor, a bis-imide dicarbox-
ylic acid containing a dimethylsilane unit, bis[N-(4-carboxy-
phenyl)phtalimidyl]dimethylsilane, prepared in our laboratory
and for the first time structurally characterized and commer-
cially available bipyridyl derivatives, 4,40-bipyridyl, 1,2-bis(4-
pyridyl)ethylene, and 4,40-azopyridine as proton acceptors, to
prepare supramolecular structures self-assembled by hydro-
gen bonds. Different from other silicon derivatives, when it is
placed among aromatic neighbors, besides improves solubility,
introduces a r–p conjugation and therefore favors electron
transport along macromolecular chains.27 On the other hand,
bipyridine derivatives have received much attention in the
design of new molecular materials for optoelectronics.28 The
presence of the pyridyl ring that is an electron-deficient aro-
matic heterocycle with a localized lone pair of electrons in the
sp2 orbital on nitrogen atom improves the electron transport-
ing properties.29 Different from similar compounds reported
in literature by us25 and others,12,30 having liquid crystal
behavior, this time we obtained polymers in the form of single
crystals, which are also desirable in electronics. The structures
of the derived supramolecular polymers were investigated by
Fourier transform infrared (FTIR) and proton magnetic reso-
TGA was performed on a STA 449F1 Jupiter NETZSCH (Ger-
many) equipment. The measurements were made in the tem-
ꢁ
perature range of 20–700 C under a nitrogen flow (50 mL/
min) using a heating rate of 10 ꢁC/min. Alumina crucible
was used as sample holder.
DSC measurements were conducted on a DSC 200 F3 Maia
(Netzsch, Germany). About 9 mg of sample was heated in
pressed and punched aluminum crucibles at a heating/cool-
ing rate of 10 ꢁC/min. Nitrogen was used as inert atmos-
phere at a flow rate of 100 mL/min. A heating rate of 10
ꢁC/min was applied.
The surface images were obtained with a Solver PRO-M
scanning probe microscope (NT-MDT, Russia) in AFM config-
uration. Rectangular silicon cantilevers NSG10 (NT-MDT, Rus-
sia) with tips of high aspect ratio were used. All images
ꢁ
were acquired in air, at room temperature (23 C), in tapping
mode, and at a scanning frequency of 1.56 Hz. The scan
length ranged between 5 and 20 lm.
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Water vapor sorption capacity of the samples was deter-
mined in dynamic regime (DVS), in the relative humidity
(RH) range of 0–90% by using the fully automated gravimet-
ric analyzer IGAsorp produced by Hiden Analytical (Warring-
ton, UK).
mixture of methanol/THF 1:1 in 3 weeks. When recrystalli-
zation occurred in THF only,
a structural modification
resulted, 2ꢂ0.5THF.
FTIR mmax (KBr), cmꢀ1: 3479w, 3415m, 2956w, 2923w,
1776m, 1728vs, 1693s, 1639w, 1610m, 1583w, 1514m,
1427m, 1411m, 1377s, 1353s, 1319s, 1294s, 1265m, 1222w,
1184w, 1178w, 1126m, 1112w, 1099m, 1089m, 1064m,
1020w, 979vw, 954w, 914w, 858m, 829m, 813m, 800m,
771m, 736m, 713w, 688w, 678w, 671w, 655vw, 632vw,
X-ray Crystallography
Crystallographic measurements for Compounds 1–5 were
carried out with an Oxford-Diffraction XCALIBUR E CCD dif-
fractometer equipped with graphite-monochromated Mo Ka
radiation. The crystals were placed 40 mm from the CCD de-
tector. The unit-cell determination and data integration were
carried out using the CrysAlis package of Oxford Diffrac-
tion.32 All structures were solved by direct methods using
1
547w, 505w, 468w, 418vw, 395w. H NMR (DMSO-d6, 400.13
MHz, d, ppm): d ¼ 13.07 (2H-COOH), 8.15–7.58 (14H-aro-
matic), 0.79 (6H-Me).
Synthesis of Supramolecular Polymer Based on Bis[N-(4-
carboxyphenyl)phtalimidyl]dimethylsilane and 4,40-Bipyr-
idyl (SP1)
SHELXS-9733 and refined by full-matrix least squares on Fo
2
with SHELXL-9733 with anisotropic displacement parameters
for nonhydrogen atoms. All H atoms attached to carbon were
introduced in idealized positions (dCH ¼ 0.96 Å) using the ri-
ding model with their isotropic displacement parameters
fixed at 120% of their riding atom. Positional parameters of
the H attached to O atoms were obtained from difference
Fourier syntheses and verified by the geometric parameters
of the corresponding hydrogen bonds.
In a 50-mL round-bottom flask equipped with magnetic stir-
rer and reflux condenser, 0.1000 g (0.17 ꢃ 10ꢀ3 mol) of 2
and 0.0265 g (0.17 ꢃ 10ꢀ3 mol) of 4,40-bipyridyl in 20 mL
mixture of methanol/THF 1:1 as solvent were introduced.
The reaction mixture was heated to reflux for 1 h. Single
crystals of supramolecular polymer were obtained by slow
evaporation of the solvents mixture in a few days at room
temperature.
CCDC 865257 (1), CCDC 865255 (2), CCDC 865256
(2ꢂ0.5THF), CCDC 865254 (SP1), and CCDC 865258 (SP3)
contain the supplementary crystallographic data for this con-
tribution. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (þ44) 1223-336-033; or
deposit@ccdc.ca.ac.uk).
FTIR mmax (KBr), cmꢀ1: 3427m, 2922w, 2792w, 2428m,
1890w, 1780m, 1724vs, 1604s, 1537w, 1512m, 1492w,
1467w, 1409m, 1367s, 1317s, 1290s, 1272s, 1217m, 1180m,
1122m, 1105m, 1082m, 1062s, 1018m, 1006m, 966w, 918m,
864m, 854m, 823m, 804s, 792m, 775s, 738s, 711w, 690w,
680m, 653w, 628m, 594w, 567w, 528w, 514m, 497w, 466w,
416w, 385vw.
Procedure
Synthesis of Supramolecular Polymer Based on
Bis[N-(4-carboxyphenyl)phtalimidyl]dimethylsilane
and 1,2-Bis(4-pyridyl)ethylene (SP2)
Synthesis of Bis(3,4-dicarboxyphenyl)dimethylsilane
Anhydride (1)
In a 100-mL round-bottom flask equipped with magnetic stir-
rer and reflux condenser having attached CaCl2 tube, 3.8800 g
(10ꢀ2 mol) of bis(3,4-dicarboxyphenyl)dimethylsilane and 50
mL of acetic anhydride were placed. The reaction mixture was
heated to reflux for 8 h. The white crystals resulted after cool-
ing at room temperature were filtered, washed with diethyl
In a 50-mL round-bottom flask equipped with magnetic stir-
rer and reflux condenser were introduced 0.1000 g (0.17 ꢃ
10ꢀ3 mol) of 2 and 0.0309 g (0.17 ꢃ 10ꢀ3 mol) of 1,2-bis(4-
pyridyl)ethylene in 20 mL mixture of methanol/THF 1:1 as
solvent. The reaction mixture was heated to reflux for 1 h.
Single crystals of supramolecular polymer were obtained by
slow evaporation of the solvents mixture in a few days at
room temperature.
ꢁ
ether, and dried (yield: 2.85 g, 81%, m.p. ¼ 180–181 C).
FTIR mmax (KBr), cmꢀ1: 3415m, 2962m, 2923w, 2854w, 1855s,
1811s, 1774vs, 1639m, 1618 m, 1407m, 1384m, 1321m,
1276s, 1253s, 1184w, 1116s, 1064s, 1024m, 910s, 877s, 837s,
813s, 790s, 731s, 702m, 676m, 636w, 595w, 582w, 545m,
FTIR mmax (KBr), cmꢀ1: 3415m, 2923w, 2426w, 1934w,
1780m, 1724vs, 1604s, 1560m, 1510m, 1469w, 1415m,
1371s, 1315m, 1286s, 1272s, 1217m, 1199m, 1186m,
1176m, 1120s, 1103m, 1083s, 1060s, 1014s, 975m, 956m,
918m, 854m, 825s, 792s, 775s, 736s, 711m, 690w, 680m,
667w, 651w, 632w, 594vw, 559m, 547m, 514m, 495w, 464w,
414w, 397vw, 387w.
1
505w, 487w, 424w, 401w. H NMR (acetone-d6, 400.13 MHz, d,
ppm): d ¼ 8.05–8.15 (6H-aromatic), 0.79 (6H-Me).
Synthesis of Bis[N-(4-carboxyphenyl)phtalimidyl]dimethyl-
silane (imidic diacid) (2) and (2ꢂ0.5THF)
About 2.8500 g (8 ꢃ 10ꢀ3 mol) of 1 and 2.2200 g (16 ꢃ
10ꢀ3 mol) of p-aminobenzoic acid were dissolved together in
50 mL glacial acetic acid, and then the mixture was refluxed
for 16 h, after which the mixture was filtered. The white
solid separated from the filtrate by cooling was washed with
Synthesis of Supramolecular Polymer Based on
Bis[N-(4-carboxyphenyl)phtalimidyl]dimethylsilane and
4,40-Azopyridine (SP3)
In a 50-mL round-bottom flask equipped with magnetic stir-
rer and reflux condenser, 0.1000 g (0.17 ꢃ 10ꢀ3 mol) of 2
and 0.0312 g (0.17 ꢃ 10ꢀ3 mol) of 4,40-azopyridine in 20
mL mixture of methanol/THF 1:1 as solvent were placed.
ꢁ
ethanol and dried (yield: 3.77 g, 79%, m.p. ¼ 331 C). Single
crystals of this dicarboxylic acid, 2, were obtained from a
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SCHEME 1 Synthesis of bis(3,4-dicarboxyphenyl)dimethylsilane anhydride (1).
The reaction mixture was heated to reflux for 1 h. Single
crystals of supramolecular polymer were obtained by slow
evaporation of the solvents mixture in a few days at room
temperature.
rical stretching vibration of carbonyl groups of imide),
whereas the band for C¼¼O of carboxylic group can be seen
at 1693 cmꢀ1. The absorption bands for dimethylsilane unit
(SiACH3) are also present at 1265 and 813 cmꢀ1. In the 1H
NMR spectrum of imidic diacid, the absorption signals of the
aromatic protons appear in the region 7.58–8.15 ppm. The
peaks corresponding to proton resonance from dimethylsi-
lane units appear at 0.79 ppm and that from COOH group
appear at 13.07 ppm, with their intensity ratios correspond-
ing to the presumed structure.
FTIR spectrum (KBr pellet), cmꢀ1: 3417s, 2956w, 2923m,
2854w, 2428w, 2345w, 1953vw, 1892w, 1847vw, 1780m,
1724vs, 1639m, 1600s, 1546w, 1510m, 1462w, 1411s,
1382vs, 1367s, 1286s, 1222m, 1222m, 1180m, 1120s,
1103m, 1080s, 1060m, 1049m, 1012m, 964w, 918m, 846s,
823m, 792m, 775s, 736s, 709w, 680m, 665w, 651w, 630w,
621w, 568m, 545m, 514m, 497m, 462w, 410vw, 387w.
It is well known that bifunctional monomeric units with
complementary groups (proton donor and proton acceptor)
can be incorporated into the polymer backbone by self-
assembling. The self-assembly of carboxylic acids as proton
donors with pyridyl fragments as proton acceptors is most
frequently used in the formation of hydrogen-bonded struc-
tures.11,12,25,28 We choose three commercially available pyri-
dine derivatives, 4,40-bipyridyl, 1,2-bis(4-pyridyl)ethylene,
and 4,40-azopyridine, to build supramolecular polymers, SP1,
SP2, and SP3, respectively, with above-synthesized dicarbox-
ylic acid, 2 (Scheme 3). The conditions created for self-
assembling consisted of the reactants heating at 65 ꢁC in a
mixture of 1:1 methanol/THF, followed by slow evaporation
of the solvents at room temperature when crystalline prod-
ucts are formed. In two of the cases (SP1 and SP3), the crys-
tals were suitable for single crystal X-ray diffraction.
RESULTS AND DISCUSSION
A silicon-containing tetracaboxylic acid, bis(3,4-dicarboxy-
phenyl)diphenylsilane, prepared according to literature
data31 was converted to the corresponding dianhydride, 1,
by refluxing in acetic anhydride (Scheme 1). The anhydriza-
tion reaction occurrence was verified by FTIR spectroscopy
that evidenced the presence of the separated compound of
the anhydride absorption bands at 1855 and 1774 cmꢀ1 in
the spectrum besides those for dimethylsilane units at 1253
1
and 813 cmꢀ1. In H NMR spectrum, the signals of aromatic
protons appear in the region 8.05–8.15 ppm, whereas the
peak corresponding to proton resonance from dimethylsilane
units appear at 0.79 ppm, with their intensity ratios corre-
sponding to the presumed structure.
The separated reaction products were first verified by FTIR
spectroscopy in which the formation of the H bond is sup-
ported by the presence of the absorption bands at 1940 and
The anhydride prepared as above described was reacted
with an excess of p-aminobenzoic acid to obtain a dicarbox-
ylic acid containing imide cycles, 2 (Scheme 2).34 In the IR
spectrum of the reaction product (Supporting Information
Fig. S1), characteristic absorption bands of imide groups
appear at 1776 and 1728 cmꢀ1 (asymmetrical and symmet-
SCHEME 2 Reaction pathway to bis[N-(4-carboxyphenyl)phtali-
midyl]dimethylsilane (2).
SCHEME 3 Chemical structure of the supramolecular poly-
mers: SP1, SP2, and SP3.
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band in complexes, and C0A is the concentration of the mono-
mer in complexes. The values thus determined for the asso-
ciation constants, between 2.10 ꢃ 102 and 4.27 ꢃ 102, sug-
gest relatively low polymerization degrees.
TABLE 1 Spectroscopic Parameters of Supramolecular
Polymers
Molar Absorption
Coefficient
[dm3/(mol cm)]
Association
Constants
(dm3/mol)
Structural Characterization
Compound
The dianhydride 1, dicarboxylic acid 2, and their derived
crystalline form 2ꢂ0.5THF, and supramolecular polymers
SP1 and SP3 were obtained as single crystals suitable for
structural investigation by X-ray diffraction. The main crys-
tallographic data together with refinement details are sum-
marized in Table 2.
SP1
SP2
SP3
1,025
661
2.10 ꢃ 102
4.15 ꢃ 102
4.27 ꢃ 102
313
2428 (SP1), 1934 and 2426 (SP2), and 1892 and 2428
cmꢀ1 (SP3) (Supporting Information Fig. S1).35,36 In the
same time, a slight shift, of about 4 cmꢀ1, to low wavenum-
bers is registered for the imide and carboxylic C¼¼O bands.
Bis(3,4-dicarboxyphenyl)dimethylsilane anhydride (1)
According to X-ray single-crystal study, the crystal structure
of 1 is built from molecular entities depicted in Figure 1.
The assembling of these asymmetric units into the 3D supra-
molecular architecture occurs through the short CAH…O
interactions, which is evidenced by the geometrical parame-
ters summarized in Table 3. The perspective view of the
crystal structure packing is shown in Figure 2.
1H NMR spectra of the products in DMSO revealed the pres-
ence of the monomeric species in nonassociated form. Other-
wise, it is known that in polar organic solvents (e.g., DMSO,
DMF, methanol, and acetonitrile), the solvent H-bonding com-
petes with the bonds between the monomeric units leading
to the dispersion of these. Although hydrogen bonding is
strengthened in a nonpolar solvent, the choice of the solvent
systems is restricted by solubility of the compounds to be
used. Unfortunately, the supramolecular structures proved to
have low solubility in nonpolar solvents (i.e., chloroform) in
which the self-assembly is to be favored.
Bis[N(4-carboxyphenyl)phtalimidyl]dimethylsilane (2)
The molecular structure of Compound 2 along with the atom
numbering scheme is shown in Figure 3. Both the crystallo-
graphic-independent carboxylic groups are involved in the
formation of the stable cyclic hydrogen-bonded system (Ta-
ble 3). As a result, the main packing motif in structure 2 is
represented by a wavy 1D chain, as depicted in Figure 4.
The system of intermolecular interactions is completed by
(i) the short CAH…p contacts between silane–methyl group
and imidic cycle of adjacent molecule with C17-H…centroid
distance equal to 2.75 Å, and (ii) the weak intermolecular
CAH…O hydrogen bonds, as shown in Table 3. These interac-
tions are responsible for the supramolecular aggregation of
the 1D chains in the crystal into 2D layers (Supporting Infor-
mation Fig. S2) and 3D network (Supporting Information Fig.
S3).
Many techniques can be used to determine the association
constant: isothermal titration calorimetry,37 1H NMR,38 UV–
vis,39,40 and temperature-dependent SAXS methods.41 IR
spectroscopy in solution and in the solid state has also been
found to be a powerful tool to investigate the nature and the
dynamics of the hydrogen bonds.42 We chose to determine
this parameter by using FTIR spectroscopy in solid state. In
this aim, the samples were incorporated in dry KBr and
processed as pellets, whose thickness was 1 mm, in order to
be measured. The FTIR spectra of the diacid and complexes
show a characteristic band attributed to the diacid carbonyl
stretching vibration at 1728 cmꢀ1 (free acid) and 1724 cmꢀ1
(in complexes). The diacid and base concentrations in com-
plexes were obtained directly by application of the Beer-
Lambert law, knowing the absorbance of the C¼¼O character-
istic band and the molar absorption coefficient of the donor–
acceptor complex. The free diacid concentration in KBr pel-
lets was 9.3 ꢃ 10ꢀ3 mol/dm3, and concentrations of the
complexes were varied between 7.37 ꢃ 10ꢀ3 mol/dm3 to
22.11 ꢃ 10ꢀ3 mol/dm3 (SP1) and 7.1 ꢃ 10ꢀ3 mol/dm3 to
21.3 ꢃ 10ꢀ3 mol/dm3 (SP2 and SP3) in KBr pellets to per-
form the calibration curve and to determine the molar
absorption coefficient (Table 1). The association constant in
The crystal structure of bis[N(4-carboxyphenyl)phtalimidyl]-
dimethylsilane 0.5THF, 2ꢂ0.5THF, resembles the structure of
2. It contains one THF solvate molecules and two discrete
molecules (denoted as A and B) of bis[N(4-carboxyphe-
nyl)phtalimidyl]dimethylsilane in the asymmetric part of the
unit cell as crystallographically independent units, which ex-
hibit similar geometric parameters (Supporting Information
Fig. S4). The three-dimensional supramolecular packing
motif of the two structures is also very similar, being
directed by the analogous OAH…O and CAH…O intermolecu-
lar contacts (see Table
3 and Supporting Information
Fig. S5).
The X-ray molecular cocrystals structure of bis[N(4-carboxy-
phenyl)phtalimidyl]dimethylsilane with 4,40-bipyridine (SP1)
and 4,40-azopyridine (SP3) are depicted in Figures 5 and 6.
the complex was determined according to
a method
described in the literature43 by using Becker procedure:
A0 ꢀ A
The geometric characteristics of the hydrogen bonds are
listed in Table 3. X-ray single-crystal study has shown that
despite different lengths of the pyridine components, SP1
and SP3 cocrystals give quite similar crystal structure. Both
structures crystallize in monoclinic system with close unit-
K ¼
;
A ꢃ CA0
where A0 is the monomer absorbance band for KBr pellet at
a known concentration, A is the absorbance of the same
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TABLE 2 Crystallographic Data, Details of Data Collection, and Structure Refinement Parameters
Compound
1
2
2ꢂ0.5THF
SP1
SP3
Empirical formula
C
18H12O6Si
C32H22N2O8Si
590.61
C68H53N4O17Si2
1254.32
C42H30N4O8Si
746.79
C42H30N6O8Si
774.81
Molecular weight (g/mol)
Temperature (K)
352.37
200(2)
0.71073
Triclinic
P1
200(2)
200(2)
200(2)
200(2)
˚
Wavelength (A)
0.71073
Monoclinic
P21/c
0.71073
0.71073
0.71073
Monoclinic
P21/c
Crystal system
Space group
Monoclinic
P21/c
Monoclinic
P21/m
˚
a (A)
8.9813(4)
9.1968(4)
10.5184(5)
93.542(4)
106.742(4)
101.800(4)
807.62(6)
2
18.843(5)
7.592(5)
21.091(5)
90
18.210(3)
13.9594(11)
24.377(3)
90
6.5888(13)
47.400(5)
27.998(3
90
6.5630(6)
48.666(4)
22.8165(19)
90
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
115.390(5)
90
109.165(16)
90
95.599(15)
90
99.139(8)
90
3
˚
V (A )
2726(2)
4
5853.2(13)
4
8702(2)
10
7195.0(11)
8
Z
Dcalc (g/cm3)
1.449
1.439
1.423
1.425
1.431
l (mmꢀ1
min–hmax (ꢁ)
)
0.178
0.145
0.141
0.132
0.132
h
2.28–25.99
2.43–26.00
2.29–25.50
2.54–25.50
2.46–22.50
Crystal size (mm)
0.10 ꢃ 0.10
ꢃ 0.05
0.15 ꢃ 0.15
ꢃ 0.05
0.15 ꢃ 0.10
ꢃ 0.05
0.20 ꢃ 0.10
ꢃ 0.10
0.10 ꢃ 0.10
ꢃ 0.05
Reflections collected
per unique
5,735/3,166
9,748/5,301
25,457/10,875
34,740/16,299
25,322/9,370
(Rint ¼ 0.0210)
3,166/0/228
(Rint ¼ 0.0993)
5,301/0/390
(Rint ¼ 0.1333)
10,875/5/801
(Rint ¼ 0.1001)
16,299/0/1261
(Rint ¼ 0.0921)
9,370/0/1,032
Data/restraints/parameters
a
R1 [I > 2r(I)]
0.0431
0.0822
0.0998
0.0992
0.0986
b
wR2 [I > 2r(I)]
0.0918
0.0841
0.1397
0.1164
0.1740
a
R1 (all data)
0.0602
0.2650
0.2569
0.2566
0.1797
b
wR2 (all data)
0.0982
0.1251
0.1766
0.1619
0.2076
GOFc
1.006
0.869
1.002
0.921
1.076
3
˚
Dqmax and Dqmin (e/A )
0.334 and ꢀ0.212
0.260 and ꢀ0.307
c
0.706 and ꢀ0.877
GOF ¼ { [w(Fo ꢀ Fc2)2]/(n ꢀ p)}1/2, where n is the number of reflec-
0.426 and ꢀ0.332
0.560 and ꢀ0.265
P
P
P
a
2
R1
¼
||Fo| ꢀ |Fc||/ |Fo|.
P
P
wR2 ¼ { [w (Fo ꢀ Fc2)2]/ [w(Fo2)2]}1/2
.
tions and p is the total number of parameters refined.
b
2
cell parameters (Table 2). The main packing motif is the
same in both crystals and is represented by a wavy chain
formed by an alternating sequence of 4,40-bipyridyl (for
SP1), 4,40-azopyridine (for SP3), and bis[N(4-carboxyphe-
nyl)phtalimidyl]dimethylsilane molecules linked by OAH…N
hydrogen bonds between carboxylic groups as donor and the
nitrogen atoms as acceptor (Table 3). It should be noted that
above-mentioned H-bonds are accompanied by the presence
of a short CAH…O interaction with the formation of the
hydrogen-bonded synthon, as shown in Figures 5 and 6:
sion of the crystal structure in both cocrystals occurs
through numerous CAH…O contacts, which sustain a 3D
The CAH…O distances are in the range between 2.60–2.88 Å
and 2.54–2.76 Å for SP1 and SP3, respectively. The exten-
FIGURE 1 X-ray molecular structure of Compound 1.
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TABLE 3 Characteristics of the Donor–Acceptor (D–A) Hydrogen Bonds in the Structures of the Prepared Compounds
˚
Distance (A)
Compound
D–HꢂꢂꢂA
D–H
HꢂꢂꢂA
DꢂꢂꢂA
DHA Angle (ꢁ)
Symmetry Code for A
1
C3-HꢂꢂꢂO3
C4-HꢂꢂꢂO1
C17-HꢂꢂꢂO4
O7-HꢂꢂꢂO1
0.93
0.93
0.96
0.83
2.63
2.46
2.56
1.81
3.500(2)
3.231(2)
3.341(3)
2.629(5)
157.0
141.0
138.8
170.3
ꢀx ꢀ 1, ꢀy, ꢀz
x, 1 þ y, z
x, y, z ꢀ 1
1
2
ꢀ1 þ x, ꢀ3=2 ꢀ y, ꢀ = þ z
2
1
O2-HꢂꢂꢂO8
0.85
1.77
2.616(5)
170.7
1 þ x, ꢀ3=2 ꢀ y, = þ z
2
1
1
C22-HꢂꢂꢂO4
0.93
0.93
0.93
0.93
0.90
0.93
0.90
0.90
0.96
0.96
0.93
0.93
0.93
0.82
0.82
0.82
0.82
0.82
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.82
0.82
0.82
0.82
2.55
2.49
2.59
2.65
1.81
1.76
1.76
1.75
2.64
2.66
2.59
2.65
2.65
1.85
1.84
1.85
1.82
1.83
2.34
2.35
2.29
2.37
2.61
2.60
2.88
2.69
2.75
1.84
1.86
1.83
1.86
3.078(7)
3.261(6)
3.389(6)
3.529(7)
2.655(6)
2.668(7)
2.627(6)
2.647(6)
3.581(8)
3.602(8)
3.205(7)
3.566(8)
3.365(8)
2.666(8)
2.659(7)
2.655(7)
2.639(7)
2.639(7)
3.23(1)
116.0
140.3
143.8
159.0
153.3
166.6
160.9
170.8
165.1
167.1
124.0
169.6
136.8
174.3
176.2
167.4
172.2
170.2
161.3
148.4
136.8
153.1
127.6
126.5
121.8
126.4
124.6
171.0
174.6
168.2
174.1
1 ꢀ x, = þ y, = ꢀ z
2
2
1
1
2
C4-HꢂꢂꢂO1
2 ꢀ x, = þ y, = ꢀ z
2
C30-HꢂꢂꢂO8
C31-HꢂꢂꢂO2
ꢀx, ꢀ1 ꢀ y, ꢀz
ꢀx ꢀ 1, ꢀy, ꢀz
1
1
2
2ꢂ0.5THF
O1A-HꢂꢂꢂO8A
O7A-HꢂꢂꢂO2A
O1B-HꢂꢂꢂO8B
O7B-HꢂꢂꢂO2B
C16B-HꢂꢂꢂO4A
C16B-HꢂꢂꢂO5A
C15B-HꢂꢂꢂO5B
C12A-HꢂꢂꢂO3B
C31B-HꢂꢂꢂO3A
O3-HꢂꢂꢂN6
1 þ x, = ꢀ y, = þ z
2
1
1
2
ꢀ1 þ x, = ꢀ y, ꢀ = þ z
2
1
1
2
1 þ x, ꢀ = ꢀ y, = þ z
2
1
1
2
ꢀ1 þ x, ꢀ = ꢀ y, ꢀ = þ z
2
1 ꢀ x, ꢀ1 ꢀ y, 1 ꢀ z
x, y ꢀ 1, z
1
1
2
1 ꢀ x, y ꢀ = , = ꢀ z
2
1 ꢀ x, ꢀ1 ꢀ y, 1 ꢀ z
1
1
2
1 ꢀ x, y ꢀ = , = ꢀ z
2
SP1
x, y, z
O11-HꢂꢂꢂN9
O19-HꢂꢂꢂN8
O15-HꢂꢂꢂN10
O7-HꢂꢂꢂN7
ꢀ1 þ x, þy, þz
x, þy, 1 þ z
1 ꢀ x, 1 ꢀ y, 1 ꢀ z
ꢀx, 1 ꢀ y, 1 ꢀ z
1 ꢀ x, 1 ꢀ y, 1 ꢀ z
x ꢀ 1, y, z
C92-HꢂꢂꢂO8
C12-HꢂꢂꢂO2
3.18(1)
C33-HꢂꢂꢂO6
3.039(9)
3.229(8)
3.26(1)
x ꢀ 1, y, z
x ꢀ 1, y, z
C63-HꢂꢂꢂO14
C87-HꢂꢂꢂO4
x, y, z
C91-HꢂꢂꢂO8
3.242(9)
3.460(9)
3.328(9)
3.362(9)
2.657(7)
2.677(7)
2.639(7)
2.678(7)
ꢀx, 1 ꢀ y, 1 ꢀ z
x, y, z ꢀ 1
1 þ x, y, z
1 ꢀ x, 1 ꢀ y, 1 ꢀ z
x, y, z
C99-HꢂꢂꢂO20
C102-HꢂꢂꢂO12
C108-HꢂꢂꢂO16
O8A-HꢂꢂꢂN3A
O7B-HꢂꢂꢂN3B
O1B-HꢂꢂꢂN6B
O2A-HꢂꢂꢂN6A
SP3
x, y, z
x, y, z
1
1 ꢀ x, = þ y, 3=2 ꢀ z
2
C37B-HꢂꢂꢂO2B
C33A-HꢂꢂꢂO7A
C40B-HꢂꢂꢂO8B
C33B-HꢂꢂꢂO2B
C40A-HꢂꢂꢂO1A
0.93
0.93
0.93
0.93
0.93
2.63
2.76
2.72
2.38
2.26
3.261(9)
3.397(9)
3.364(9)
3.26(1)
126.1
126.5
126.8
158.2
170.3
x, y, z
x, y, z
x, y, z
1 þ x, þy, þz
2 ꢀ x, ꢀ = þ y, 3=2 ꢀ z
1
3.182(9)
2
C6A-HꢂꢂꢂO3A
C41A-HꢂꢂꢂO1A
0.93
0.93
2.30
2.54
3.062(8)
3.204(9)
138.4
128.9
ꢀ1 þ x, þy, þz
1
1 ꢀ x, ꢀ = þ y, 3=2 ꢀ z
2
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FIGURE 4 One-dimensional infinite chain in crystal structure 2.
On DSC traces, besides melting and crystallization processes,
glass transitions have been identified for all of three supra-
molecular structures (Table 4). Their values in the second
run were determined to be 12.5, 15.8, and 7.5 ꢁC for SP1,
SP2, and SP3, respectively (Fig. 9). The presence of the glass
transition is a proof for the polymeric nature because, as it
is known, at this temperature, portions of the molecules
begin to wiggle around and the polymer passes in its rub-
bery state. The transition around this temperature could be
assigned mainly to flexible CASiAC segment encased in rigid
ones.
FIGURE 2 The fragment of crystal packing in 1. Hydrogen
bonds are shown by dashed lines.
two-component supramolecular architecture, as shown in
Figures 7 and 8. The three-dimensional packing in structure
SP3 essentially results from the parallel packing of the wavy
layers in 011 orientation (see Fig. 8).
Thermal Analysis
The results of the TGA analysis performed in nitrogen atmos-
phere, as given in Table 4, revealed four-step decomposition
in all cases (Supporting Information Fig. S6). Based on the
weight loss percent in the first main stage, it could corre-
spond to the bipyridyl derivative decomposition. The less
stable proved to be the compound containing 4,40-bipyridyl,
which showed the main decomposition peak at 167 ꢁC. All
samples show a high amount of residue (between 34.2% for
SP1 and 62.7% for SP3) at 700 ꢁC that could be a SiACAN
material.
AFM Measurements
The ability of the prepared supramolecular polymers to self-
assemble at microscale was emphasized by AFM. The AFM
images were taken on the film surface prepared by spin
coating from solution in THF and evaluated in terms of aver-
age roughness (Sa), root mean square roughness (Sq), core
fluid retention index (Sci), developed interfacial area ratio
(Sdr), and texture direction index (Stdi), as can be seen in
Table 5. Detailed definitions of these parameters can be
found in ref. 44. The tapping mode height images on flat sur-
face (Fig. 10) reveal different morphologies. The film
obtained for the sample SP1 presents a compact, globular
morphology. Height profile analysis along each globule meas-
ures an average diameter of 122 6 17 nm. For the sample
SP2, a fibrous organization on extended length (1–4 lm)
and height (14–60 nm) was observed. This suggests that the
supramolecular polymers are assembled into
a bundle,
adopting coiled superstructures, as the literature revealed in
similar cases.45 This is also supported by the low value of
the texture direction index (Stdi ¼ 0.54) obtained for this
sample (Table 5), which indicates a predominant texture rel-
ative to the rest of the surface. When AFM image obtained
for SP2 is compared with those achieved for SP1 and SP3
(Fig. 10), it can be observed that SP2 is more homogeneous
and exhibited a greater isotropy, as indicated by directional-
ity. In the case of SP3 compound, the structuration results in
porous material. The highest value of the developed interfa-
cial area ratio, Sdr, indicates that of all samples, SP3 devel-
ops the most complex morphology. The aspect of the pores
was characterized by means of porosity (7 pores per lm2),
FIGURE 3 X-ray structure of Compound 2.
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FIGURE 5 X-ray structure of one of five crystallographic independent 1D supramolecular infinite chain in crystal structure SP1.
mean diameter, and mean depth calculated on 5 ꢃ 5 lm2
scanning area. Thus, the appearance of pores on the surface
with average diameter of 211 6 90 nm and average depth
of 50 6 6 nm (calculated on 182 collected pores, using
height profile analysis) resulted in a high value of average
and root mean square roughness (Table 5).
values of this index for SP1 (1.19) and SP3 (1.22) were
obtained. This leads to the conclusion that the samples SP1
and SP3 behave similarly, both having lower sorption when
compared with SP2 sample.
Moisture Sorption
The moisture sorption in polymer is very important for a va-
riety of industries ranging from microelectronics to adhe-
sives and coatings.46 To study the behavior of the crystalline
supramolecular compounds in the presence of the humidity,
the sorption–desorption isotherms were registered in
dynamic regime. The sample was dried at 25 ꢁC in flowing
Regarding the capacity of the samples SP1–SP3 to retain flu-
ids, the core fluid retention index, Sci, was calculated (Table
5). The highest value of Sci achieved for SP2 (1.52) is an in-
dication of good fluid retention in the core zone for this sam-
ple and hence high sorption capacity. Moreover, very close
FIGURE 6 A and B symmetric part in the unit cell in the crystal structure of SP3.
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FIGURE 7 Crystal structure packing in SP1.
nitrogen (250 mL/min) until the constant weight at RH <
1% was obtained. Then the RH was gradually increased
from 0 to 90% in 10% humidity steps, each step having a
pre-established equilibrium time between 10 and 20 min so
as the sorption equilibrium to be achieved every time. Then,
the RH decreased when the desorption curves were regis-
tered. The obtained isotherms at room temperature are pre-
sented in Figure 11 (inset).
FIGURE 8 View of the crystal structure along a crystallographic axis in SP3.
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TABLE 4 The Main Thermal Parameters for the Supramolecular
TABLE 5 The 3D Roughness Parameters Calculated from AFM
Polymers
Images Obtained for the Prepared Supramolecular Structures
Peak
DSC
Parameters
SP1 SP2
SP3
Roughness Parameters
SP1
SP2
SP3
Saa (nm)
Sqb (nm)
Scic
Sdrd (%)
Stdie
5.90
7.70
1.19
4.16
0.79
3.46
4.26
1.52
0.20
0.54
12.34
14.67
1.22
First run heating Tg (ꢁC)
Tm (ꢁC)
First run cooling Tc (ꢁC)
14.8 16.6
104.7 70.4
8.8
95.6
77.6 Undetected 76.0
12.5 15.8 7.4
5.21
Second run
heating
Tg (ꢁC)
0.76
a
Average roughness.
Root mean square roughness.
Tm (ꢁC)
107.4 Undetected 96.0
b
c
Core fluid retention index.
TGA
d
Developed interfacial area ratio.
Tpeak (ꢁC)
167
25.2 3.2
278 315
14.7 17.4
439 436
19.7 23.7
210
200
14.1
279
9.6
e
Peak 1
Texture direction index.
Weight loss (%)
Tpeak (ꢁC)
Peak 2
attributed to the packing pattern, with the polar groups being
the same. The moisture sorption behavior well correlates with
AFM observations as well as with the calculated values.
Weight loss (%)
Tpeak (ꢁC)
Peak 3
416
9.7
Weight loss (%)
Tpeak (ꢁC)
The isotherms show hysteresis between the adsorption and
desorption cycles at RH > 60%; this being usually attributed
to pore effects.50 This is supported by the fact that SP2
which, according to AFM images, is the most porous has
highest sorption capacity and that hysteresis occurs at RH
60%. In the case of SP1, the isotherm is closed by desorp-
tion, a weight change occurs in SP2 and SP3 of about 0.48
and 0.96%, respectively, most probably as a result of the
hydration of the carboxylic groups favored by the adequate
packing of the macromolecules, as revealed by AFM images.
Peak 4
520
6.0
516
8.3
510
3.7
Weight loss (%)
T (ꢁC)
End process
700
700
700
62.7
Residual mass (%) 34.2 45.5
The isotherms of SP1 and SP2 can be assimilated as isotherms
of Type III according to IUPAC classification; this type describ-
ing hydrophobic or low hydrophilic materials with low sorp-
tion at low RH, sometimes moderate sorption at the middle
RH, and suddenly high water sorption at increased RH.47 The
SP3 isotherm is rather of Type II, a sigmoid isotherm, charac-
teristic of strong physical adsorption followed by multilayer
absorption.48,49 Relatively low values were obtained for the
water sorption capacity, ranging between 2.36 and 9.67% for
the samples SP1 and SP2, respectively (Table 6). The hydro-
phobic character is accentuated by the presence of the dime-
thylsilane units. The differences between samples could be
The increase in temperature results in a significant increase
in sorption capacity, as can be seen in Figure 11. Thus, the
humidity uptake increases about five times in the case of the
sample SP2, whereas in the sample SP3, it increases to 1.5
times (Table 6). This is somewhat unexpected because, as is
known, sorption processes are generally exothermic.51,52
There could be several reasons for this. High temperatures
not only increase the diffusion rate of the water molecules52
but also the hygroscopicity of the compound.53 Water sorp-
tion is based on the existence of the hydrophilic sites.54
These polar sites either exist, and are progressively uncov-
ered due to the disorganization of the crystals as the tem-
perature increases, or they are created by hydrogen bonds
dissociation. At low temperatures, the rate of H-bond dissoci-
ation is slow,53 whereas at high temperatures, this process
intensifies favoring the molecular transport.
CONCLUSIONS
A silicon-containing dicarboxylic acid prepared by us accord-
ing to an already reported procedure and for the first time
structurally characterized, bis[N-(4-carboxyphenyl)phtalimi-
dyl]dimethylsilane, was found to self-assemble both itself
and with bipyridyl derivatives in supramolecular polymers
by hydrogen bonds. These were first emphasized by FTIR
spectroscopy and subsequently confirmed by X-ray single-
crystal diffraction. TGA revealed the bipyridyl derivative to
be weak thermal links in the supramolecular structures.
High amounts of residues remained after thermal
FIGURE 9 DSC scans: second run for the samples SP1, SP2,
and SP3.
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FIGURE 10 Tapping mode 3D height AFM images of the samples SP1–SP3 prepared on flat surface.
as electronic devices. Glass transitions were identified for all
structures by DSC analysis, this being a proof for the poly-
meric nature of the compounds. The supramolecular com-
pounds proved to be able for structuration in film in differ-
ent patterns depending on the structure. The structure also
determines the behavior of the crystalline supramolecular
compounds in the presence of the humidity, with the maxi-
mum sorption capacity ranging from 2.36% in the case of
the compound based on 4,40-bipyridyl to 9.67% for 1,2-
bis(4-pyridyl)ethylene. These values significantly increase
(2.5–5 times) with the increase in the temperature.
ACKNOWLEDGMENTS
This research was financially supported by the European
Regional Development Fund, Sectoral Operational Programme
‘‘Increase of Economic Competitiveness,’’ Priority Axis 2 (SOP
FIGURE 11 The shape of the moisture sorption–desorption
IEC-A2-O2.1.2-2009-2, ID 570, COD SMIS-CSNR: 12473, Con-
tract 129/2010-POLISILMET). The authors also thank Mihaela
Avadani for helpful discussions on the association constant
determination.
isotherms.
decomposition of all compounds in nitrogen atmosphere, this
being an advantage for application in certain domains such
TABLE 6 Water Sorption Capacity for the Supramolecular
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