A Novel siloxane-containing dicarboxylic acid, 1,3-bis(p-carboxyphenylene- ester-methylene)tetramethyldisiloxane, and its derivatives: Ester macrocycle and supramolecular structure with a copper complex

Article abstract of DOI:10.1016/j.tet.2014.02.061

The new dicarboxylic acid, 1,3-bis(p-carboxyphenylene-ester-methylene) tetramethyldisiloxane (H₂L, 1) was obtained by treating 1,3-bis(chloromethyl)-1,1,3,3-tetramethyldisiloxane with a mixture of terephthalic acid and terephthalic acid sodium salt in a 1:1 ratio. In this approach, besides the desired compound 1 (33 wt % yield), the condensation cyclic dimer 2 (7 wt % yield) and an oligomer 3 (10 wt % yield) resulted. The reaction between dicarboxylic acid H₂L, where L is the carboxylate ligand, along with imidazole as co-ligand, and copper hydroxide resulted in the formation of a coordination compound [Cu(HIm)₄(H₂O) ₂]L·4.5H₂O (4). Single-crystal X-ray crystallography has revealed that the crystal structure of 4 is a self-assembled H-bonded three-dimensional supramolecular structure. FTIR and NMR spectral techniques were also used to characterize the formed structures. Optical and thermal properties of all compounds were studied. The stability of the supramolecular structure in solution (methanol) and with temperature was studied using ATR-FTIR. The ability of the macrocycle 2 to bind potassium cations in solution was investigated by UV-vis spectrophotometry.

Full text of DOI:10.1016/j.tet.2014.02.061

Tetrahedron 70 (2014) 2661e2668
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A Novel siloxane-containing dicarboxylic acid,
1,3-bis(p-carboxyphenylene-ester-methylene)
tetramethyldisiloxane, and its derivatives: ester macrocycle and
supramolecular structure with a copper complex
*
Mirela-Fernanda Zaltariov, Angelica Vlad, Maria Cazacu , Sergiu Shova, Mihaela Balan,
Carmen Racles
“Petru Poni” Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, 700487 Iasi, Romania
a r t i c l e i n f o
a b s t r a c t
Article history:
The new dicarboxylic acid, 1,3-bis(p-carboxyphenylene-ester-methylene)tetramethyldisiloxane (H2L, 1)
was obtained by treating 1,3-bis(chloromethyl)-1,1,3,3-tetramethyldisiloxane with a mixture of tereph-
thalic acid and terephthalic acid sodium salt in a 1:1 ratio. In this approach, besides the desired com-
pound 1 (33 wt % yield), the condensation cyclic dimer 2 (7 wt % yield) and an oligomer 3 (10 wt % yield)
resulted. The reaction between dicarboxylic acid H2L, where L is the carboxylate ligand, along with
imidazole as co-ligand, and copper hydroxide resulted in the formation of a coordination compound
[Cu(HIm)4(H2O)2]L$4.5H2O (4). Single-crystal X-ray crystallography has revealed that the crystal struc-
ture of 4 is a self-assembled H-bonded three-dimensional supramolecular structure. FTIR and NMR
spectral techniques were also used to characterize the formed structures. Optical and thermal properties
of all compounds were studied. The stability of the supramolecular structure in solution (methanol) and
with temperature was studied using ATR-FTIR. The ability of the macrocycle 2 to bind potassium cations
in solution was investigated by UVevis spectrophotometry.
Received 24 October 2013
Received in revised form 11 February 2014
Accepted 24 February 2014
Available online 2 March 2014
Keywords:
Carboxylate ligand synthesis
Macrocyclic ligand
Siloxane derivative
Esterification
Spectroscopic analysis
Hydrogen bonds
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
has gained increasing attention in the past few years is the p/p
stacking interaction between aromatic rings. Although this in-
teraction is not as directional as hydrogen bonding, an order of
stability in the interaction of two
Metal-organic frameworks (MOFs), built on the principles of
coordination chemistry, combine the desirable properties of the
individual organic and inorganic components, having applications
in different fields such as gas storage, gas separation and hetero-
geneous catalysis,1e3 sensors,4e6 nonlinear optics (NLO),7 ion ex-
change,8,9 and magnetism.10,11 A wide variety of architectures has
been prepared by connecting rigid metallic building blocks, con-
sidered as secondary building units (SBUs), with organic linkers by
covalent bonds. The use of multidentate carboxylate ligands as
organic linkers for the metallic SBU units has been studied exten-
sively, due to the advantage of the neutrality of the resulting net-
works without to be required the presence of counterions.12e14 Less
rigid, but highly organized structures can also be assembled by
noncovalent supramolecular interactions. The hydrogen bond is
often used in the construction of supramolecular networks pri-
marily due to its high directionality.15e17 Another interaction, which
p
systems was well established.18
The most frequently used and studied ligands, which can bridge
metal cations for MOF building are rigid aromatic dicarboxylic
acids.19,20 Less attention has been given to metaleorganic archi-
tectures with flexible ligands, of due to the difficulties in predicting
the structures of the formed complexes as well as in their charac-
terization. However, there are examples in the literature according
to which MOFs characterized by flexible and tunable pores show
attractive properties of sorption and selectivity. In addition, the ar-
chitecture of flexible MOFs can suffer structural rearrangement
in the sorption process, self-adjusting their topology to the
shape or size of the guest molecules, as a result of interaction with
these.21 Recently, it has been shown that flexible multidentate
ligands (e.g., malonate,22 1,4-cyclohexanedicarboxylic acid,23
1,2,3,4,5,6-cyclohexanehexacarboxylic acid,24 and tetrahydrofur-
antetracarboxylic acid,25 cyclohexane-1,2,4,5-tetracarboxylic acid,26
5-(3,5-dicarboxybenzyloxy)-3-pyridine carboxylic acid),21 in the
presence of a suitable co-ligand, can to develop systems with dif-
ferent dimensionality and coordination styles.27,28 Bis(oxy)
* Corresponding author. E-mail address: mcazacu@icmpp.ro (M. Cazacu).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.02.061

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M.-F. Zaltariov et al. / Tetrahedron 70 (2014) 2661e2668
isophthalic acid ligands with CH2e and (CH2)2e spacers, which
confer flexibility to the tetracarboxylic acid were utilized in the
construction of two- and three-dimensional coordination polymers
by reacting them with a variety of the oxophilic lanthanoid metal
ions.29 In our previous work,30e32 we reported new MOFs of Co(II),
Zn(II), and Cu(II) based on some dicarboxylic acids containing the
corresponding to the protons from SieCH3 and SieCH2, re-
spectively. Their intensity ratio (Ar/eCOOH/SieCH3/
SieCH2¼2:1:3:1) corresponds to the presumed structure. 13C NMR
spectrum (Fig. 3S) also confirms the formation of diacid, 1.
In the FTIR spectrum of cyclic compound 2ꢀ, 1the characteristic
absorption bands for ester group at 1720 cm , for SieOeSi at
1065 cmꢀ1, and for SieCH3 at 839 and 1258 cmꢀ1 were observed
(Fig. 6Sa). In the 1H NMR spectrum of the cyclic compound 2 (Figs.
7Se9S), the signals for aromatic protons appear at 8.83 ppm, while
the peaks corresponding to resonance of the protons from SieCH3
and SieCH2 appear at 0.23 and 3.99 ppm, and their intensity ratio
(Ar/SieCH3/SieCH2¼1:3:1) corresponds to the presumed structure.
13C NMR spectrum (Fig. 10S) also confirms the formation of the
cyclic compound.
flexible
tetramethyldisiloxane
moiety,
namely
1,3-
bis(carboxypropyl)tetramethyldisiloxane, and heterocyclic co-
ligands: 4,40-azopyridine30e32 or imidazole.31,32 In the effort to de-
velop complexes containing flexible moieties, we report here a new
siloxane-containing dicarboxylic acid that was prepared and char-
acterized. Within its synthetic procedures, two new compounds,
formed as by-products, were structurally characterized. The main
reaction product having free carboxyl groups was used as a co-
ligand for Cu(II) ion besides imidazole. A 3D supramolecular struc-
ture consisting in a [Cu(HIm)4(H2O)2]2þ and L2ꢀ units connected
through hydrogen bonding interactions was obtained. Thermal and
solvolytic stability of this structure was evaluated. The ability of the
macrocycle to complex an alkali-metal cation was investigated by
UVevis spectrophotometry.
In the FTIR spectrum of the siloxane oligomer, 3, the charac-
teristic absorption bands for ester group at 1720 cmꢀ1, and for
dimethylsiloxane moiety at 1067 cmꢀ1 (SieOeSi), 839 and
1258 cmꢀ1 (SieCH3) were observed (Fig. 6Sb). In the 1H NMR
spectrum of the siloxane oligomer, 3, (Fig. 11S), the signals of ar-
omatic protons appear at 8.21e7.23 ppm, while the peaks corre-
sponding to resonance of the protons from SieCH3 and SieCH2
appear at 0.28e0.11 and 4.08e4.00 ppm; their intensity ratio
corresponds to the presumed structure. 13C NMR spectrum
(Fig. 12S) also confirms the formation of the siloxane oligomer
compound.
The siloxane-containing diacid 1 was reacted with freshly pre-
pared copper hydroxide in presence of imidazole (Scheme 2), and
blue crystals suitable for X-ray diffraction were obtained.
In the FTIR spectrum of Cu(II) complex 4 (Fig. 1Sb) the specific
bands for eC]N from imidazole at 1556 cmꢀ1 are present, while
those specific for carboxylic and ester groups are shifted at
1698 cmꢀ1 (shoulder-carboxylic) and at 1717 cmꢀ1 (ester group).
2. Results and discussion
A new siloxane-containing diacid, 1, was prepared by the re-
action of 1,3-bis(chloromethyl)-1,1,3,3-tetramethyldisiloxane with
a 1:1 mixture of terephthalic acid sodium salt and terephthalic acid
(Scheme 1). It is well known that in each polycondensation re-
action, besides linear, cyclic oligomers are also formed. In our case,
two compounds were obtained during the purification steps of
diacid, one, labeled 2, as crystals suitable for X-ray diffraction, and
another, labeled 3, an oligomer resin, the structure of which was
determined by NMR spectroscopy (Scheme 1).
Scheme 1. Reactions leading to the mixture of compounds 1, 2, and 3.
In the FTIR spectrum of 1,3-bis(p-carboxyphenylen-ester-
methylene)tetramethyldisiloxane, 1, the characteristic absorption
The absorption bands characteristic for hydrogen bonds between
carboxylic group, imidazole, and coordinated water molecules are
also visible in the FTIR spectrum of the complex in the region
2600e1900 cmꢀ1. The participation of carboxylic acid groups in the
formation of hydrogen bonds is supported by the shift of carboxylic
band to higher frequencies compared with the starting diacid,
while the absorption band specific for ester group is shifted at
lower frequencies. The characteristic bands for siloxane and di-
bands for carboxylic acid at 1692 and 3431 cmꢀ1
(n OH), ester
group at 1722 cmꢀ1, for SieOeSi at 1067 cmꢀ1, and for SieCH3 at
839 and 1256 cmꢀ1 were observed (Fig. 1Sa). In the 1H NMR
spectrum of the diacid 1, (Figs. 2S, 4S, and 5S), the signals of aro-
matic protons appear at 8.03e8.05 ppm, while the peak corre-
sponding to resonance of the carboxylic protons appears at
13.32 ppm. Other peaks are those at 0.19 and 3.99 ppm
methyl silane groups appear at 1069 and 1259 cmꢀ1
.

M.-F. Zaltariov et al. / Tetrahedron 70 (2014) 2661e2668
2663
Scheme 2. Complexation reaction of Cu(II) with 1,3-bis(p-carboxyphenylen-ester-methylene)tetramethyldisiloxane and imidazole.
2.1. Structural characterization
According to X-ray single-crystal study, compound 2 has a mo-
lecular structure built up from discrete neutral macrocyclic units
(Fig. 1), resulting from the 2þ2 condensation of 1,3-
bis(chloromethyl)-1,1,3,3-tetramethyldisiloxane and terephthalic
acid. To the best of our knowledge, compound 2 is the first example
of a macrocyclic derivative of terephthalic acid containing a 1,1,3,3-
tetramethyldisiloxane fragment.
Fig. 2. View of the asymmetric part of the unit cell in the crystal structure 4. Thermal
ellipsoids are drawn at 40% probability level. Non-relevant H atoms, as well as the
solvate water molecules are omitted for clarity.
conformation and does not coordinate to copper atom. In the
crystal, the discrete [Cu(HIm)4(H2O)2]2þ and L2ꢀ ions are connected
by the coordinated and solvated water molecules into a three di-
mensional supramolecular network through intermolecular
OeH/O hydrogen bonding (Fig. 13S). In this arrangement, the 3D
architecture is consolidated by numerous NeH/O hydrogen bonds
formed between coordinated imidazole molecules as donors and
oxygen atoms of carboxylate groups and water molecules as ac-
ceptors. The H-bond parameters in the crystal structure 4 are
Fig. 1. X-ray molecular structure of 2. Thermal ellipsoids are drawn at 50% probability
level.
summarized in Table 1. On the other hand, the
pep stacking in-
teraction between adjacent centrosymmetrically related imidazole
ꢀ
rings, evidenced by the short (3.652 A) centroid-to-centroid dis-
The
crystal
structure of
compound
4
comprises
tance, should also be mentioned.
[Cu(HIm)4(H2O)2]2þ complex cations, L2ꢀ anions and statistically
distributed solvate water molecules in 1:1:4.5 ratio. A view of the
asymmetric part of the unit cell is shown in Fig. 2. In the complex
cation, each copper atom is coordinated by four neutral imidazole
ligands and two water molecules within a slightly distorted octa-
In order to study the stability of compound 4 in solution, ATR-
FTIR was used. The solution containing the Cu(II) complex (2 mg
in 1 mL methanol) was applied to the ZnSe crystal surface and the
spectra were measured every minute until the solvent evaporated,
at room temperature (Fig. 14Sb). Initially, in the FTIR spectra the
specific bands of methanol (broad band at 3400 cmꢀ1 (OH groups),
ꢀ
hedron. The average CueN bond lengths (2.013(4) A) along with the
CueO distances (2.542(3) A) are comparable to those found in
2945 and 2883 cmꢀ1 (eCH3 groups) and 1660 cmꢀ1
(nOH group) are
ꢀ
earlier studied complexes with similar copper environment.33 The
geometric parameters of the structure 4 are summarized in Table
1S. Doubly deprotonated tetramethyldisiloxane-containing di-
present. During the evaporation of methanol, the hydrogen bonds
between coordinated water molecules, imidazole, and carboxylic
acid reformed and all the characteristic bands of compound 4 ap-
pear, analogous with the spectrum measured in solid state,
carboxylic acid (L2ꢀ
) counter-anion is in a fully transoid

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M.-F. Zaltariov et al. / Tetrahedron 70 (2014) 2661e2668
Table 1
Table 2
H-bonds parameters for compound 4
The main parameters of the thermograms
ꢀ
DeH/A
Distance, A
Angle
DeH/A,
Symmetry code
Compound
Peak
(step)
T (ꢁC)
The mass
loss, %
The rest, %
17.60
ꢁ
D/H
H/A
D/A
Ton
Tmax.
Tof
O1weH/O1
O1weH/O3w
O2weH/O7
O2weH/O9
O3weH/O8
O3weH/O9w
N2eH/O4w
N2eH/O5w
N4eH/O8
0.86
0.83
0.87
0.85
0.85
0.87
0.86
0.86
0.86
0.86
0.86
1.96
2.19
2.04
1.90
2.08
2.12
2.10
2.25
1.87
2.25
1.88
2.794(5)
2.924(6)
2.891(5)
2.745(5)
2.895(6)
2.73(1)
2.91(1)
2.99(2)
2.730(5)
3.003(6)
2.737(6)
162.8
147.2
165.6
172.6
160.0
126.8
156.5
144.0
174.8
146.3
174.2
1þx, 1þy, z
i, y, z
1
I
II
214.67
272.93
218.21
278.02
348.80
466.97
325.15
433.98
471.65
362.03
450.92
69.01
270
366.94
1.71
42.90
2ꢀx, 2ꢀy, 2ꢀz
x, y, z
III
I
II
430.66
286.16
354.66
500.91
332.16
498.21
37.38
4.12
76.94
2ꢀx, 2ꢀy, 2ꢀz
x, y, z
2
18.28
1ꢀx, 2ꢀy, 2ꢀz
x, 1þy, z
3
4
I
II
I
II
III
IV
334.70
399.79
59.39
109.04
218.85
256.73
399.00
484.39
79.34
135.26
256.00
334.20
16.08
65.64
4.03
5.98
18.94
49.40
16.75
20.99
2ꢀx, 2ꢀy, 1ꢀz
2ꢀx, 2ꢀy, 2ꢀz
2þx, 1þy, z
N6eH/O3w
N8eH/O2
118.76
230.01
276.05
indicating the regeneration of the initial structure: 3298 cmꢀ1
(
nOH), 1698 cmꢀ1 (carboxylic C]O), 1717 cmꢀ1 (ester C]O),
decomposition of 1 begins at 214 ꢁC, when solvent molecules (DMF)
are lost. The second and third steps are due to loss of the organic
moieties. In the case of compound 4, the decomposition that begins
at 59 ꢁC is due to the loss of solvent molecules, while in the second
step that occurs at 109 ꢁC, the dissociation of hydrogen bonds and
the loss of the coordinated water molecules take place.34 The last
two stages of decomposition of the metal complex that correspond
to the loss of the ligands moieties, occur at lower temperatures than
dicarboxylic acid. This is possible by the catalytic action of the metal
in the decomposition process. The decomposition of compounds 2
and 3 occurs in two steps and starts at higher temperatures as
compared with compounds 1 and 4 indicating the absence of sol-
vent in their masses and good thermal stability.35,36 This is attrib-
uted to the presence of a larger number of aromatic ester groups in
their structures (four ester groups in the structure of compound 2
as compared with two ester groups in the case of compound 1).
The data from the DSC study (Fig. 17S, Table 3) reveal
that compound 3 shows a glass transition at ꢀ25.32 ꢁC in the DSC
curve. The presence of the siloxane moiety in its structure confers
glass transition at a lower temperature as compared with other
aromatic polyesters. In the DSC curve of the cyclic compound 2, the
melting and the crystallization peaks are present. The melting peak
and glass transition are also present in the DSC curve of compound
1, while in the case of compound 4, the presence of the glass
transition at 46.77 ꢁC supports the polymeric nature of the com-
pound that derived from self-assembling in supramolecular archi-
tectures via hydrogen bonds. However, in the first stage, this
compound has a melting temperature of about 70 ꢁC, close to the
value found by determining in capillary (76 ꢁC).
1601 cmꢀ1 (aromatic), 1556 cmꢀ1 (imidazole C]N), 1259, 841 cmꢀ1
(SieCH3), 1069 cmꢀ1 (SieOeSi). The broad bands in the range
2660e1900 cmꢀ1 are attributed to the hydrogen bonds.
The hydrogen bond dynamics of compound 4 with temperature
has been investigated using an ATR-FTIR spectrometer equipped
with a temperature controller. The spectra were recorded at each
increase in temperature by 5 ꢁC up to the first thermal de-
composition stage as evidenced by thermogravimetric analysis (see
below). The structural changes induced can be seen in Fig. 15S. In
the spectra of compound 4 during the heating procedure the spe-
cific broad bands of the OH stretching vibrations at 3720 cmꢀ1
appeared due to dissolution of the hydrogen bonds present in the
region 3300e3120 cmꢀ1. An important feature of compound 4 is
that the structural changes on increasing the temperature are re-
versible. By cooling at the same rate, the initial spectrum is ob-
tained, indicating that the specific structural hydrogen bonds
between carboxylic OH groups and imidazole were re-formed.
The thermal stability of all prepared compounds was in-
vestigated by thermogravimetric analysis in nitrogen atmosphere.
The main parameters of the thermogravimetric (Fig. 3) and DTG
(Fig. 16S) curves are collected in Table 2.
Table 3
The main parameters of the differential scanning calorimetry curves
Compound
Scan
Tg (oC)
Tm (ꢁC)
Tcr (oC)
1
First heating
cooling
22.49
d
198.48
d
d
d
Second heating
First heating
cooling
Second heating
Second heating
First heating
Second heating
1.46
d
d
d
2
181.81
d
d
d
136.65
d
d
194.97
d
3
4
ꢀ25.34
d
d
69.94
d
d
46.77
d
Fig. 3. Thermogravimetric curves of compounds 1e4.
The copper complex shows an absorption in UVevis spectrum at
668 nm (
3
¼52 molꢀ1 cmꢀ1) assigned to copper ions and its in-
The thermal decomposition of dicarboxylic acid 1, and its Cu(II)
complex 4, occurs in three and four steps, respectively. The di-
carboxylic acid 1 is more stable than its Cu(II) complex 4, probably
due to the inter- and intramolecular hydrogen bonds. The
tensity decreases as concentration is lowered (Fig. 18S).
Macrocyclic compounds, such as azacrowns, crown-ethers,
silacrowns, and cryptands, are well known for their complexing
abilities for metal ions, in solution.37,38 Various applications include

M.-F. Zaltariov et al. / Tetrahedron 70 (2014) 2661e2668
2665
chemical sensors, the selective removal of poisonous or radioactive
metal cations from waste streams, membrane transport, immobi-
lization of radioisotopes, optical receptors, phase-transfer catalysts,
and cation separation.37e39 The parameters of the macrocyclic
cavity (the number, distance, and orientation of the donor atoms of
the ligand) confer selectivity for certain ions.40e42 The ability of the
solvent molecules to compete with the donor atoms of the ligand
toward the coordination sites of the cation is another factor that can
influence complexation.43 Many different macrocyclic esters have
been prepared and investigated for selective complexation.44
Valinomycin45 and nonactin46 are the best known cyclic esters for
their highly ability to form complexes with alkali cations, exhibiting
an especially selectivity for potassium ions, the stability constants
for the potassiumevalinomycin and potassiumenonactin com-
0.35, and 0.4 mL) to 3.5 mL solution of compound 2 resulted in
different molar ratios between potassium ion and the ligand. The
calculation of the stability constant was performed using the Ben-
esieHildebrand equation 1:49
ꢀ
ꢁ
ꢀ
ꢁ
½Lꢄ
1
1
¼
þ
(1)
D
A
3
Ks½Mꢄ
3
k
k
where [L], [M] and
3
k
are the concentrations of the ligand, KSCN,
and molar absorption coefficient, respectively;
absorbance at each molar ratio of KSCN to the ligand and A0 is the
D
A¼AꢀA0, [A] is the
absorbance in the absence of KSCN.
The [L]/
The plot of [L]/
D
A and [M] values are provided in Table 2S.
A versus 1/M is shown in the Fig. 5. Intercept and
D
slope of this linear plot determine the stability constant and the
molar absorption coefficient, respectively (i.e., the ratio of intercept
plexes being 106 Mꢀ1 and 38.6ꢂ1.3ꢃ103
M
ꢀ1, respectively.
Our macrocyclic compound 2 has four polar ester groups for
binding metal ions and two nonpolar tetramethyldisiloxane units
linked by two aromatic rings. The conformation of macrocycle 2
depends on the polarity of the solvent. Thus, in nonpolar organic
solvents such as chloroform, the tetramethyldisiloxane units are
targeted on the outside and the carbonyl groups inside, while for
polar solvents such as methanol the carbonyl groups are mainly
exposed.47,48 It would be expected that the size of the molecule and
the presence of the tetramethyldisiloxane moieties in the structure
make it highly flexible and allow complexation of ions. We choose
potassium as the ion to be complexed. The stability constant for
macrocycleecation complexes is the simplest measure of the
strength of complexing in solution, different techniques being used
for this: NMR titration, potentiometric titration, calorimetric titra-
tion, mass spectrometry, fluorescence and absorption spectroscopy,
and XRD for crystalline complexes.37,38,49 We used UVevis spec-
trophotometry for this study. The UVevis absorption spectrum of
compound 2 in CHCl3 exhibits two peaks at 285 nm and 296 nm
to slope is Ks and the inverse of intercept is k). The plot of [L]/DA
versus concentration of KSCN, 1/M, is linear suggesting that the
predominant species in solution is a 1:1 complex.
3
attributed to the
pep interactions in the aromatic ring. The
*
changes in the absorption spectra on addition of KSCN are shown in
Fig. 4. There is a decrease in these absorption bands as the con-
centration of cationic species in solution increases, these changes
being attributed to the formation of the metallic complex.
Fig. 5. The dependence of [L]/
ions by macrocycle 2.
DA versus 1/M in complexation process of potassium
Although smaller than that obtained for other ester macrocycles
(valinomycin and nonactin, for example),45,46 the value obtained
for our cycle, Ks¼376 Mꢀ1, indicates the formation of a moderately
stable complex.
3. Conclusions
In an attempt to prepare a new saturated dicarboxylic acid, 1,
containing siloxane fragments, two other species, i.e., a well-
defined macrocycle 2, and a oligomeric siloxane-aromatic ester, 3,
were also formed. Dicarboxylic acid, 1, was treated with freshly
prepared copper hydroxide in the presence of imidazole and an H-
bonded supramolecular structure containing complexed metal
units was obtained. All compounds were studied by spectroscopic
methods (FTIR and NMR) to establish structures. The macrocycle 2
and metal complex 4 separated as single crystals able to be ana-
lyzed by X-ray single crystal diffraction that permitted us to con-
firm their structures. The thermal studies revealed a better stability
of the macrocycle and oligomeric species to decomposition as
compared with dicarboxylic acid and its copper complex. DSC
emphasized the glass transitions in the case of compounds 3 and 4.
In methanol solution or by heating in solid state, the dissolution of
Fig. 4. Modification of UVevis spectrum as the volume of KSCN solution added to
CHCl3 solution of macrocyclic compound 2 changes (C1eC9, Table 2S).
For the determination of stability constant, Ks, of the formed
complex, solutions of compound 2 (5.33ꢃ10ꢀ4 M) in chloroform
and KSCN (5.33ꢃ10ꢀ3 M) in methanol were prepared. Addition of
different amounts of potassium salt solution (0.1, 0.15, 0.2, 0.25, 0.3,

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M.-F. Zaltariov et al. / Tetrahedron 70 (2014) 2661e2668
the hydrogen bonds occurs but these easily re-formed as methanol
evaporates as was emphasized through ATR-FTIR study. The mac-
rocyle 2 proved to be able to complex potassium cation in 1:1 M
ratio.
manufacturer. The data were collected and processed using Mass-
Hunter Workstation software.
UVevis absorption spectra measurements were carried out in
CHCl3, methanol or DMF solution on
spectrophotometer.
a
Specord 200
4. Experimental
4.1. Materials
The thermogravimetric (TG)ddifferential thermogravimetric
(DTG) analysis was performed on an STA 449F1 Jupiter NETZSCH
equipment. The measurements were made in the 20e700 ꢁC
temperature range under a nitrogen flow (50 mL/min) using
a heating rate of 10 ꢁC/min. An alumina crucible was used as sample
holder.
Differential scanning calorimetry (DSC) measurements were
conducted on a DSC 200 F3 Maia (Netzsch, Germany). About 10 mg
of sample was heated in pressed and punched aluminum crucibles
at a heating rate of 10 ꢁC/min. Nitrogen was used as inert atmo-
sphere at a flow rate of 100 mL/min. A heating and cooling rate of
10 ꢁC/min was applied.
Terephthalic
acid
(Fluka), 1,3-bis(chloromethyl)-1,1,3,3-
tetramethyldisiloxane (Fluka), sodium hydroxide (Aldrich),
CuCl2$2H2O (Aldrich), KSCN (Aldrich), Imidazole (Aldrich), acetone
(Chimopar), methanol (Chimopar), chloroform (Chimopar), dime-
thylformamide (Aldrich), diethyl ether (Aldrich) were used as re-
ceived. Terephthalic acid sodium salt was prepared as follows:
NaOH (10.00 g, 0.06 mol) was dissolved in distilled water (30 mL)
and then terephthalic acid (4.83 g, 0.12 mol) was added. After
complete dissolution of the terephthalic acid, the solution was
poured into acetone (100 mL) and a white precipitate (the ter-
ephthalic acid sodium salt) formed. The resulting sodium salt was
filtered, washed with diethyl ether, and dried in oven at 80 ꢁC for
2 h (12.00 g, 95 wt % yield). Salt formation was verified by FTIR
spectroscopy where the band at 1688 cmꢀ1 characteristic for car-
boxylic group of terephthalic acid disappeared being replaced by
a new strong band at 1564 cmꢀ1 assigned to carboxylate group
(Fig. 19S).
Melting points of the complexes were measured on a Melt-Temp
II (Laboratory Devices) apparatus.
4.3. X-ray crystallography
Crystallographic measurements for compounds 2 and 4 were
carried out with an Oxford-Diffraction XCALIBUR E CCD diffrac-
tometer equipped with graphite-monochromated Mo Ka radiation.
The crystals were placed 45 mm from the CCD detector. The unit
cell determination and data integration were carried out using the
CrysAlis package of Oxford Diffraction.50 All the structures were
solved by direct methods using Olex251 software with the SHELXS
structure solution program and refined by full-matrix least-squares
on F02 with SHELXL-97.52 Atomic displacements for non-hydrogen,
non-disordered atoms were refined using an anisotropic model.
The carbon H atoms were placed in fixed, idealized positions and
refined as rigidly bonded to the corresponding atom. Hydrogen
atoms for OH groups have been placed by Fourier Difference ac-
counting for the hybridation of the supporting atoms and the hy-
drogen bonds parameters. The molecular plots were obtained using
the Olex2 program.51 The main crystallographic data together with
refinement details are summarized in Table 4, while selected bond
lengths and angles in Table 1S. CCDC952138 (2), CCDC 952139 (4)
contain the supplementary crystallographic data. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/retrie-
ving.html (or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: þ44 1223 336 033; or
deposit@ccdc.ca.ac.uk).
4.2. Measurements
Fourier transform infrared (FTIR) spectra were recorded using
a Bruker Vertex 70 FT-IR spectrometer in the transmission mode in
the range 400e4000 cmꢀ1 at room temperature with a resolution
of 2 cmꢀ1 and accumulation of 32 scans. ATR-FTIR spectra in so-
lution were recorded using a Bruker Vertex 70 FTIR spectrometer
equipped with a ZnSe crystal. The measurements were performed
in ATR (Attenuated Total Reflectance) mode in the 600e4000 cmꢀ1
range at room temperature with a resolution of 4 cmꢀ1 and accu-
mulation of 32 scans.
Temperature-dependent ATR-FTIR spectra were recorded in
both heating and cooling runs on a Bruker Vertex 70 FT-IR In-
strument equipped with a Golden Gate single reflection ATR ac-
cessory and a temperature controller. The solid sample was added
to the ATR crystal surface and sealed with a cap to avoid solvent
evaporation. The temperature varied between 22 and 52 ꢁC being
increased by 5 ꢁC at each measurement. After the temperature was
changed, the sample was maintained for 2 min before the acqui-
sition of the spectrum.
4.4. Synthesis and characterization
The NMR spectra were recorded on a Bruker Avance DRX
400 MHz Spectrometer equipped with a 5 mm QNP direct detection
probe and z-gradients. Spectra were recorded in CDCl3 or DMSO-d6,
4.4.1. Synthesis of the siloxane-containing diacid, H2L (1). In a round
bottom flask equipped with reflux condenser, calcium chloride
tube, and magnetic stirrer, were introduced dry dimethylforma-
mide (100 mL), terephthalic acid sodium salt (8.37 g, 0.04 mol),
terephthalic acid (6.62 g, 0.04 mol), and 1,3-bis(chloromethyl)-
1,1,3,3-tetramethyldisiloxane (8.8 mL, 0.04 mol). The reaction
mixture was stirred under argon atmosphere to reflux for 24 h. The
resulting NaCl was separated by filtration and the filtrate was
poured into distilled water (300 mL), when a beige solid separated
on the glass bottom. After removing the liquid phase, the residue
was washed with distilled water (3ꢃ100 mL) and dissolved in
chloroform (100 mL) and a white precipitate, labeled as compound
1 (6.37 g, 33 wt % yield) was formed. The precipitate was filtered
and the filtrate was poured in a separatory funnel and extracted
with distilled water (3ꢃ100 mL). The organic phase was reduced to
a small volume (20 mL). Colorless crystals (1.85 g, 7 wt % yield) of
a compound 2 were obtained by slow chloroform evaporation. The
crystals were filtered, washed with diethyl ether, and dried. A beige
at room temperature. The chemical shifts are reported as
d values
(ppm). The atom labeling for the NMR assignments is that from
XRD structures. The assignments of all the signals in the 1D NMR
spectra were done using 2D NMR experiments like H,C-HMQC and
H,C-HMBC.
Mass spectra were recorded using an Agilent 6520 Series
Accurate-Mass Quadrupole Time-of-Flight (Q-TOF) LC/MS. The so-
lutions were introduced into the electrospray ion source (ESI) via
a syringe pump at a flow-rate of 0.01 mL/min. After optimization of
the Q/TOF MS parameters, they were set as follows: electrospray
ionization (positive ion mode), drying gas (N2) flow rate 10.0 L/
min; drying gas temperature 325 ꢁC; nebulizer pressure 35 psig,
capillary voltage 4200 V; fragmentation voltage 400 V; the full-scan
mass spectra of the investigated compounds were acquired in the
m/z range of 100e3000. The mass scale was calibrated using the
standard calibration procedure and compounds provided by the

M.-F. Zaltariov et al. / Tetrahedron 70 (2014) 2661e2668
2667
Table 4
170.17(carboxylic, eC]O), 166.40, 166.32, 166.30 (ester, eC]O),
134.78, 134.11, 134.03, 133.03, 130.52, 130.13, 129.44, 129.21, 129.05,
123.55 (AreC), 59.28, 58.76, 58.64, 57.93 (CH2), 1.83, 1.06, ꢀ0.52,
ꢀ0.83, ꢀ0.91, ꢀ1.01, ꢀ1.14, ꢀ1.29, ꢀ1.42 (CH3). GPC: Mn¼815,
Mw¼1051, PDI¼1.3 (Fig. 20S).
Crystallographic data, details of data collection, and structure refinement parame-
ters for 2 and 4
Compound
2
4
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
C
28H40O10Si4
C34H53CuN8O15.5Si2
941.56
200
Triclinic
P-1
11.0597(6)
15.1803(8)
15.2675(7)
111.860(5)
92.895(4)
107.273(5)
2233.8(2)
2
648.96
200
4.4.2. Preparation of [Cu(HIm)4(H2O)2]L$4H2O (4). In a 100 mL
round bottom flask equipped with magnetic stirrer and reflux
condenser, a solution consisting of CuCl2$2H2O (0.85 g, 5 mmol)
dissolved in distilled water (20 mL) was loaded after which 1 M
solution NaOH (12 mL) was added dropwise producing a pale blue
precipitate of Cu(OH)2$xH2O. The resulting solution was centri-
fuged and washed with double distilled water (3ꢃ100 mL). Sepa-
rately, a solution consisting of 1,3-bis(p-carboxyphenylen-ester-
methylene)tetramethyldisiloxane, (2.25 g, 5 mmol), 1, and of im-
idazole (HIm) (0.34 g, 5 mmol) dissolved in 100 mL methanol/
distilled water (1:1 v/v) was prepared. The Cu(OH)2 precipitate was
subsequently added to this solution, and the mixture was stirred at
reflux for 8 h after which the mixture was filtered off. The blue
filtrate was kept at room temperature and blue crystals suitable for
single crystal X-ray diffraction were formed after three weeks
(0.24 g, 28 wt % yield).
Monoclinic
P21/c
16.1929(4)
8.56278(18)
11.8252(3)
90
98.000(2)
90
1623.67(7)
2
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
ꢁ
ꢁ
a
b
g
/
/
ꢁ
/
ꢀ
V/A3
Z
Dcalcd/mg/mm3
1.327
0.236
1.400
0.616
m
/mmꢀ1
Crystal size/mm3
0.3ꢃ0.2ꢃ0.1
5.08e52
10,683
3190[Rint¼0.0375]
3190/0/194
0.0430
0.1080
1.028
0.45/ꢀ0.23
0.2ꢃ0.15ꢃ0.05
3.92e52
16,899
8569[Rint¼0.0359]
8569/0/551
0.0783
0.1979
1.054
1.42/ꢀ0.61
qmin,
q
max(ꢁ)
Reflections collected
Independent reflections
Data/restraints/parameters
R1a (I>2
s(I)
wR2b (all data)
GOFc
Mp 76 ꢁC; IR nmax (KBr, cmꢀ1): 3416s, 3298s, 3173s, 3142s,
3119s, 3059m, 2953m, 2928m, 2851m, 2727w, 2691w,
2631w, 2600w, 1717s, 1618s, 1601s, 1556s, 1537s, 1501m, 1450w,
1425m, 1387vs, 1310s, 1259s, 1173w, 1138m, 1123m, 1096s, 1069vs,
1016m, 949w, 912w, 880m, 841s, 799s, 739s, 663s, 621m, 609m,
538w, 501m. Anal. Calcd for C34H53CuN8O15.5Si2: C 43.37, H 5.67, N
3
ꢀ
Drmax and Drmin/e/A
a
R1¼SjjFojꢀjFcjj/SjFoj.
P
P
wR2 ¼ f wðF02 ꢀ Fc2Þ2= ½wðF02Þ2ꢄg1=2
.
b
c
P
GOF ¼ f wðF02 ꢀ F02Þ2=ðn ꢀ pÞg1=2, where n is the number of reflections and p
is the total number of parameters refined.
11.90. Found:
C 47.35, H 5.17, N
12.94; MS (ESIþ) found:
m/z¼1042.0270 [Mþ2H2Oþ2CH3OH]. calcd for C34H53CuN8O15.5Si2;
resin, 3, resulted after complete evaporation of chloroform (3.12 g,
[M$2H2O$2CH3OH], 1041.6746.
10 wt % yield).
Acknowledgements
4.4.1.1. Compound 1. Mp 200 ꢁC; IR nmax (KBr, cmꢀ1): 3431m,
3069w, 2961m, 2920m, 2853w, 2671w, 2552w, 2363vw, 2340vw,
1722vs, 1692vs, 1616m, 1576w, 1529w, 1508m, 1429s, 1412m,
1383w, 1302vs, 1256vs, 1175w, 1109s, 1067vs, 1018s, 943w, 878m,
839s, 799s, 756w, 731s, 554w, 503w, 473w, 449vw. 1H NMR
This work was supported by a grant of the Ministry of
National Education, CNCS & UEFISCDI, project number PN-II-ID-
PCE-2012-4-0261. The authors also express sincere thanks to
Dr. Cristian Peptu for MS spectra measurements.
(DMSO-d6, 400.13 MHz,
(8H, d, AreH), 3.99 (4H, s, eCH2), 0.19 (12H, s, CH3). 13C NMR
(DMSO-d6, 100.16 MHz, , ppm):166.46 (carboxylic, eC]O), 165.63
d, ppm): 13.32 (2H, s, COOH), 8.07e8.05
Supplementary data
d
FTIR spectra for all final products, 1H NMR and 13C NMR for
compounds 1, 2, and 3, H,C-HMQC and H,C-HMBC for compounds 1
and 2, figure showing the fragment of three-dimensional supra-
molecular network in the crystal structure of compound 4, DTG and
DSC curves for all compounds, UV spectrum for copper complex, 4,
FTIR spectrum for natrium salt of terephthalic acid natrium salt,
GPC curve for compound 3, the table containing selected bond
lengths (A) and angles ( ) for compounds 2 and 4, and the table
containing the main parameters of the BenesieHildebrand model.
Supplementary data associated with this article can be found in the
online version, at http://dx.doi.org/10.1016/j.tet.2014.02.061.
(ester, eC]O), 134.69, 133.26, 129.53, 129.12 (AreC), 58.31 (CH2),
1.00 (CH3). Anal. Calcd for C22H26O9Si2: C 53.86, H 5.34. Found: C
53.94, H 5.29; MS (ESIþ) found: m/z¼513.0407 [MþNa]þ, m/
z¼1003.0961 [2MþNa]þ. Calcd for C22H26O9Si2; [MþNa]þ,
513.5994; [2MþNa]þ, 1004.2025.
4.4.1.2. Compound 2. Mp 196 ꢁC; IR nmax (KBr, cmꢀ1): 3424w,
2961m, 2910w, 1720vs, 1612w, 1574w, 1531w, 1504w, 1410m,
1385m, 1304vs, 1258vs, 1177w, 1119s, 1103s, 1065vs, 1018s, 949w,
876m, 839s, 802s, 754w, 731s, 528w, 467w. 1H NMR (CDCl3,
ꢁ
ꢀ
400.13 MHz,
d
, ppm): 7.83 (8H, s, AreH), 3.99 (8H, s, CH2), 0.234
(24H, s, CH3). 13C NMR (CDCl3, 100.16 MHz,
d
, ppm): 166.27 (ester,
eC]O), 133.80, 129.22 (AreC), 58.89 (CH2), ꢀ0.99 (CH3). Anal.
Calcd for C28H40O10Si4: C 51.82, H 6.21. Found: C 51.84, H 6.18; MS
(ESIþ) found: m/z¼649.0990 [M], m/z¼671.0781 [MþNa]þ, m/
z¼1320.1852 [2MþNa]þ. Calcd for C28H40O10Si4; [M], 648.9516;
[MþNa]þ, 671.9413; [2MþNa]þ, 1320.8929.
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