Metallopolymeric structures containing highly flexible siloxane sequence

Article abstract of DOI:10.1016/j.polymer.2012.11.021

H-bonded supramolecular polymers based on 1,3-bis(3-carboxypropyl) tetramethyldisiloxane and 4,4′-azopyridine, 1, or imidazole, 3, were prepared and used as ligands for Co(II) and Zn(II) ions, respectively. A re-organization of the supramolecular structures occurred by introducing the metal salts, Co(ClO₄)₂ × 6H₂O and Zn(O₂CCH₃)₂ × 2H₂O, leading to the polyorganometallosiloxane structures 2 and 4, respectively. The compounds were investigated by elemental and spectral (¹H NMR, FTIR, UV-Vis, and fluorescence) analysis as well as by X-ray single crystal diffraction. Thermal behaviour of the metallopolymers was evaluated by TGA and DSC while the moisture behaviour was studied by dynamic vapour sorption analysis (DVS). Magnetic susceptibility was determined for paramagnetic Co(II)-containing polyorganometallosiloxane. The dielectric response and ac conductivity were investigated by dielectric spectroscopy at different temperatures and frequencies.

Full text of DOI:10.1016/j.polymer.2012.11.021

Polymer xxx (2012) 1e11
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Metallopolymeric structures containing highly flexible siloxane sequence
*
Angelica Vlad, Maria Cazacu , Mirela-Fernanda Zaltariov, Sergiu Shova, Constantin Turta, Anton Airinei
“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
0
Article history:
Received 4 July 2012
Received in revised form
H-bonded supramolecular polymers based on 1,3-bis(3-carboxypropyl)tetramethyldisiloxane and 4,4 -
azopyridine, 1, or imidazole, 3, were prepared and used as ligands for Co(II) and Zn(II) ions, respectively.
A
re-organization of the supramolecular structures occurred by introducing the metal salts,
Co(ClO O and Zn(O CCH ꢀ 2H O, leading to the polyorganometallosiloxane structures 2 and
ꢀ 6H
, respectively. The compounds were investigated by elemental and spectral ( H NMR, FTIR, UVeVis, and
5
November 2012
4
)
2
2
2
3
)
2
2
Accepted 6 November 2012
Available online xxx
1
4
fluorescence) analysis as well as by X-ray single crystal diffraction. Thermal behaviour of the metal-
lopolymers was evaluated by TGA and DSC while the moisture behaviour was studied by dynamic vapour
sorption analysis (DVS). Magnetic susceptibility was determined for paramagnetic Co(II)-containing
polyorganometallosiloxane. The dielectric response and ac conductivity were investigated by dielectric
spectroscopy at different temperatures and frequencies.
Keywords:
Polyorganometallosiloxane
Single crystal X-ray diffraction
Supramolecular polymer
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
the metal to weak and labile, non-covalent coordination interac-
tions that allow for reversible, ’dynamic’ binding analogous to
Synthetic polymers containing metal centers constitute an
interesting and broad class of easily processable materials with
properties and functions that are complementary to those of
organic macromolecular materials [1], the inclusion of transition
metals into polymers being a well-recognized way to introduce
specific physicochemical properties within a macromolecular
structure. Interest in such metallopolymers as new electro-
conducting, emissive and photovoltaic materials, as optical limiters,
in nanoelectronics, information storage, nanopatterning and
sensing, as macromolecular or hybrid forms of catalyst and artificial
enzymes, as stimuli-responsive and self-healing materials, in the
chemical modification of electrode surfaces for photocatalytic
purposes, etc. [1e7] has resulted in the development of a number of
routes for inclusion of metal species. A diverse range of metal
centres can be harnessed to tune macromolecular properties, from
main-group metals (p-block) and transition-metal ions (d-block) to
lanthanides and actinides (f-block elements). The metal centres can
be located either in the polymer main chain or in the side-chain
structure that can be linear, star-shaped, highly branched or
dendritic [1,8]. Moreover, the linkages that bind the metal centres,
of crucial importance in determining the properties of metal-
lopolymers [1], can vary almost continuously from strong, essen-
tially covalent bonds that lead to irreversible or ’static’ binding of
hydrogen bonding in supramolecular polymers [1,9e11].
Generally, metallo-supramolecular polymers result from the
complexation of metal ions with ditopic chelating ligands [4,5,9]. The
ligand being a telechelic system is capable of a continuous chain
extension in the presence of a metal ion by following the well-known
polycondensation-like mechanism [12]. The advantage of metal-
ligand coordination in comparison to other supra-interactions is its
high specificityand directionality. In comparison to hydrogen bonding,
which is also specific and directional, the strength of the metal coor-
dination bond can be easily tuned by changing the metal ion.
The developments in the metallopolymers also include silicone
where the research expanded to organometallosiloxanes and
polymeric derivatives, polyorganometallosiloxanes [13]. The
introduction of a metal into the polysiloxane chain was regarded as
a particular type of doping of organopolysiloxanes for modifying
their properties, mainly thermal stability. It was also found that the
introduction of metal atoms leads not only to enhance the ther-
mooxidative stabilities of organopolysiloxanes but also to improve
other properties (for example, adhesion and strength). As a conse-
quence, polyorganometallosiloxanes are used for a variety of
practical purposes (e.g., to obtain heat-resistant varnishes and for
thermal stabilization of siloxane rubbers) [14]. Polysiloxanes can be
involved either directly with siloxane bond (i.e. metal siloxides
containing SieOM linkages), most prevalent, or through the
attached organic chelating functions in 2D or 3D metal-containing
structures but these are less. There are some reports in literature on
the polymeric structures containing siloxane and complexed
*
Corresponding author.
E-mail address: mcazacu@icmpp.ro (M. Cazacu).
0
032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2012.11.021
Please cite this article in press as: Vlad A, et al., Metallopolymeric structures containing highly flexible siloxane sequence, Polymer (2012),
http://dx.doi.org/10.1016/j.polymer.2012.11.021

2
A. Vlad et al. / Polymer xxx (2012) 1e11
metals. These refer mainly to polysiloxane having pendant metal
complexed groups [15e17] and block copolymers containing
siloxane and ferrocenyl units [18e20]. Polymers containing
siloxane and other metals in the main chain are unusual [21,22].
Elemental composition was determined with Environmental
Scanning Electron Microscope (ESEM) type Quanta 200 having
coupled an energy dispersive X-ray spectroscope (EDX).
Dynamic water vapour sorption (DVS) capacity of the samples
was determined in the relative humidity (RH) range 0e90% by
using the fully automated gravimetric analyser IGAsorp produced
by Hiden Analytical, Warrington (UK).
Magnetic properties of complex at room temperature were
determined by NMR (Bruker Avance DRX 400 MHz spectrometer)
measurement using the Evans method [26e28]. The indicator
compound was t-butanol in DMSO. The “doped” solution (1 mL)
with known quantity of investigated substance (7 mg) was prepared
in a capillary tube and shift difference was measured directly. The
prepared solution was clear. The experimental data were used to
0
In this paper we prepared siloxane-4,4 -azopyridine-Co(II) and
siloxane-imidazole-Zn(II) polymers based on 1,3-bis(carboxypropyl)
tetramethyldisiloxane as the common building element. The new
1
structures were well-characterized by spectral (FTIR, H NMR, UVe
Vis, and fluorescence) analysis and X-ray single crystal diffraction.
Thermal behaviour was evaluated by TGA and DSC, while the mois-
ture behaviour was evaluated by water vapour sorption analysis in
dynamic regime (DVS). Magnetic susceptibility was determined for
paramagnetic Co(II)-containing polyorganometallosiloxane. The
dielectric response and ac conductivity were investigated by
dielectric spectroscopy at different temperatures and frequencies.
eff
determine the effective magnetic moment of complex, m .
Novoncontrol setup (Broadband dielectric spectrometer
Concept 40, Germany), integrating an ALPHA frequency response
analyser and a Quatro temperature control system, was used to
investigate the dielectric properties over a broad frequencies
2
. Experimental
2.1. Materials
0
6
ꢁ
ꢁ
window, 10 e10 Hz, in the ꢂ140 C to þ50 C temperature range.
2
1,3-Bis(3-carboxypropyl)tetramethyldisiloxane,
Samples compressed at 10 t/cm to form pellets with 13 mm
[
HOOC(CH (CH Si] O, Cx, was synthesized using the method
2
)
3
3
)
2
2
diameter and 0.5 mm thickness were placed between gold plated
described in Ref. [23] (the hydrolysis of 1,3-bis(3-cyanopropyl)-
round electrodes. Dielectric data were collected at constant
ꢁ
ꢂ1
ꢁ
tetramethyldisiloxane); m.p. ¼ 50 C. IR
n
max (KBr), cm : 3041m,
temperature as
between ꢂ140 C and þ50 C. The bias voltage applied across the
a
function of frequency at every
5
C
ꢁ
ꢁ
2
2
959s, 2944s, 2899s, 2887s, 2704m, 2653m, 2622m, 2568w,
521w, 1813w, 1715vs, 1460m, 1428s, 1404m, 1356w, 1315m,
sample was 1.0 V.
1
305m, 1275m, 1257s, 1249s, 1232vs, 1171w, 1073vs, 1018s, 973m,
67m, 944m, 836vs, 814s, 799s, 789s, 769s, 736m, 706m, 680w,
Fluorescence spectra were obtained by using a Perkin Elmer
LS55 luminescence spectrometer in solution or in solid state.
9
6
0
1
56w, 625w, 512w. H NMR (CDCl
3
),
3
d, ppm: 0.04 (s, SieCH ), 0.52e
.56 (m, eCH eSi), 1.60e1.68 (m, eCH
2
2
e), 2.32e2.36 (m, eCH
2
e
2.2.1. X-ray crystallography
COOH), and 11.39 (s, COOH), 84% yield; intensity ratio: 3:1:1:1:0.5.
Crystallographic measurements for 1, 2, and 4 were carried out
with an Oxford Diffraction XCALIBUR E CCD diffractometerequipped
with graphite-monochromated Mo-K radiation. The crystals were
a
0
4
,4 -azopyridine, C10
H
8
N
4
, was prepared according to known
ꢁ
procedure reported in literature [24,25], m.p. 95e105 C.
Other reactants: Imidazole,
perchlorate, Co(ClO O (Sigma Aldrich); Zinc acetate mon-
ꢀ 6H
ohydrate, Zn(O CCH O (Chimopar S.A.).
ꢀ 2H
C
3
H
4
N
2
(Aldrich); Cobalt(II)
placed 40 mm from the CCD detector. The unit cell determination
and data integration were carried out using the CrysAlis package of
4
)
2
2
2
3
)
2
2
Oxford Diffraction [29]. All structures were solved by direct methods
2
Solvents: methanol and ethanol (Chimopar S.A.), tetrahydro-
furan and diethyl ether (Aldrich) were used as received.
using SHELXS-97 [30] and refined by full-matrix least-squares on F
o
with SHELXL-97 [30]. Non-disordered non-H atoms were treated
anisotropically in all structures. In 2, non-coordinated 1,3-
bis(carboxypropyl)tetramethyldisiloxane molecules was found to
be disordered over two positions. The combined anisotropic/
isotropic refinement has been used for non-H atoms in this disor-
dered fragment. Isotropical refinement was also applied for the
chlorine atoms with SOF of positions equal or less than 0.2 in the
2.2. Measurements
Fourier transform infrared (FTIR) spectra were recorded using
a Bruker Vertex 70 FTIR spectrometer. Registrations were per-
ꢂ1
formed in the transmission mode in the range 400e4000 cm at
ꢂ1
0
0
0
room temperature with a resolution of 2 cm and accumulation of
(2,2 ,6,6 -tetrachloro)-4.4 -azopyridine ligand. All H atoms attached
to carbonwere introduced in idealized positions (dCH ¼ 0.96 Å) using
the riding 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 bythe geometric parameters of thecorresponding hydrogen
bonds. The main crystallographic data together with refinement
details are summarized in Table 1.
3
2 scans.
1
The proton magnetic resonance ( H NMR) spectra were acquired
ꢁ
in CDCl
3
at 25 C with a Bruker Avance DRX 400 MHz spectrometer
1
operating at 400.13 MHz for H. The spectrometer was equipped
with a 5 mm four nuclei, direct detection z-gradient probe head.
Chemical shifts are reported in ppm and are referenced to CDCl
3
1
d
H ¼ 7.26 ppm.
UVeVIS absorption spectra were recorded on spectrophotom-
CCDC-881459 (1), CCDC-881458 (2), and CCDC-881460 (4)
contain the supplementary crystallographic data for this contri-
bution. These data can be obtained free of charge via www.ccdc.
cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: þ44 1223 336 033; or deposit@ccdc.ca.ac.uk).
eter Shimadzu UV-1700 using quartz cuvettes of 1 cm width.
The thermogravimetric analyses were performed on a STA
4
49F1 Jupiter NETZSCH (Germany) equipment. The measurements
ꢁ
were made in the temperature range 20e900 C under a nitrogen
flow (50 mL/min) using a heating rate of 10 C/min. 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 were heated in pressed and punched aluminium cruci-
2.3. Procedure
2.3.1. Synthesis of supramolecular polymer (1) based on 1,3-bis(3-
carboxypropyl)tetramethyldisiloxane and 4,4 -azopyridine
ꢁ
0
bles at a heating rate of 10 C/min. Nitrogen was used as inert
atmosphere at a flow rate of 100 mL/min. A heating and cooling rate
of 10 C/min was applied.
In a 50 mL round bottom flask equipped with magnetic stirrer,
and reflux condenser having attached CaCl tube were dissolved
2
ꢁ
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A. Vlad et al. / Polymer xxx (2012) 1e11
3
Table 1
1227m, 1252s, 1302w, 1321m, 1385s, 1421s, 1454s, 1489m, 1533vs,
549vs, 1570s, 1603s, 1724w, 2799w, 2874m, 2924m, 2955m,
113m, 3418s, 3466s.
UVeVis (DMSO):
max ¼ 452 nm (ε ¼ 132 mol Lcm ).
Crystallographic data, details of data collection and structure refinement parameters
for the prepared compounds.
1
3
ꢂ1
ꢂ1
Compound
1
C
2
C
N
4
C
l
max ¼ 292 nm (ε ¼ 6270 mol Lcm );
ꢂ1
ꢂ1
Empirical formula
22
H
34
4
N O
5
Si
2
34
H
57.4CoCl0.6
15
H
28
N
2
O
5
Si
2
Zn
l
4
O10Si
4
Molecular weight, 490.71
g/mol
874.80
437.94
2
.3.3. Synthesis of supramolecular polymer (3) based on 1,3-bis(3-
carboxypropyl)tetramethyldisiloxane and imidazole
Temperature, (K)
Wawelength, (Å)
Crystal system
Space group
a, (Å)
200(2)
0.71073
200(2)
200(2)
0.71073
triclinic
P-1
0.71073
monoclinic
P2 /c
In a 50 mL round bottom flask equipped with magnetic stirrer,
and reflux condenser were dissolved 0.1500 g (0.49 mmol) 1,3-
bis(3-carboxypropyl)tetramethyldisiloxane in 10 mL ethanol and
monoclinic
C2/c
32.478(3)
9.7548(8)
8.3467(7)
90
91.259(8)
90
2643.7(4)
4
1
12.1261(9)
13.3922(9)
14.895(2)
91.897(8)
92.347(8)
112.337(7)
2232.4(4)
2
6.777(5)
36.763(5)
8.858(5)
90
100.337(5)
90
2171(2)
4
1.340
0
.0333 g (0.49 mmol) imidazole was then added. The mixture was
b, (Å)
c, (Å)
stirred under reflux for 1 h and then was left to stand at room
temperature. The solution remained homogeneous for long time
ꢁ
a
, ( )
ꢁ
b
, ( )
(several weeks). Then, the solvent was evaporated under vacuum
ꢁ
g
, ( )
and a colourless paste was obtained.
3
V, (Å )
ꢂ1
IR
n
max (KBr), cm : 3148w, 1955s, 2899w, 2876m,2583vw,
Z
D
m
3
calc (g/cm )
ꢂ1
1.233
0.172
2.51 to 26.00
1.301
0.581
2.36 to 26.00
2505w, 1967w, 1715s, 1595m, 1547m, 1443m, 1410m, 1385m,
1329w,1290w,1254vs,1223m,1171w,1121m,1965vs, 974w, 942vw,
8
, (mm
)
1.266
2.40 to 26.00
0
q
min,
q
max( )
85m, 839vs, 797vs, 706w, 660m, 636m, 462vw.
Crystal size (mm) 0.10 ꢀ 0.10 ꢀ 0.05 0.15 ꢀ 0.15 ꢀ 0.05 0.15 ꢀ 0.05 ꢀ 0.01
ꢂ1
ꢂ1
UVeVis (DMSO):
lmax ¼ 278 nm (115 mol Lcm ).
Reflections
5712/2593
18,004/8729
[Rint ¼ 0.038]
0.0727
0.2006
1.019
13,162/4256
[Rint ¼ 0.0728]
0.0774
0.1524
1.092
Fl (DMSO):
lem ¼ 392 nm.
collected/unique Rint ¼ 0.0489]
a
R
1
(I > 2
s(I))
0.0713
0.1133
1.004
b
wR
2
(all data)
2.3.4. Synthesis of the metallopolymer 4
c
GOF
1,3-Bis(3-carboxypropyl)tetramethyldisiloxane
(0.1500
g,
Drmax and Drmin
(
0.226 and ꢂ0.267 1.249 and ꢂ0.899 0.914 and ꢂ0.729
e/Å3)
0.49 mmol) was dissolved in 5 mL methanol in a 50 mL round
bottom flask equipped with magnetic stirrer. Over this solution was
added successively, in drops under vigorous stirring a solution
a
b
c
R
wR
1
¼ SjjF
o
j ꢂ jF
c
jj/SjF j.
o
2
2 2
2
)2]}1/2.
2
¼ {S[w (F
o
ꢂ F
c o
) ]/S[w(F
2
2
2
1/2
consisting in 0.1070 g (0.49 mmol) Zn(O
CCH
)
2
2
ꢀ 2H O and 2 mL
GOF ¼ {S[w(F
o
ꢂ F ) ]/(n ꢂ p)} , where n is the number of reflections and p is
c
2
3
the total number of parameters refined.
distilled water and the solution of 0.0667 g (0.98 mmol) imidazole
in 3 mL water. The reaction mixture was stirred at room tempera-
ture for 2 h after which the clear solution was left to stand in
laboratory conditions. Crystals as transparent, flexible foils grew
during about one month. These were separated by filtration,
washed with water, methanol and petroleum ether and dried at
room temperature. Yield: 0.14 g, 65.3%. The compound is insoluble
in common organic solvents.
0
.1500 g (0.49 mmol) 1,3-bis(3-carboxypropyl)tetramethyldisilox-
0
ane in 10 mL ethanol. 0.0900 g (0.49 mmol) freshly purified 4,4 -
azopyridine was then added. The mixture was stirred 20 min after
which 2.0530 g (0.49 mmol) 2,6-dimethylpyridine was added fol-
lowed by refluxing for 1 h and then was left to stand at room
temperature. An orange crystalline mass separated after about one
Elem. anal. %wt., Found: C40.10; H6.80; N6.53; Calculated for
month. By re-crystallizing from CHCl
suitable for X-ray single crystal diffraction were formed. The
product is soluble in CHCl , CH CN, THF.
Elem. anal., %wt: Found, %: C52.35; H6.42; N11.57. Calcd for
3
/CH
3
CN (1/1) large crystals
C
15
H
IR
28
N
2
O
5
Si
2
Zn (M ¼ 437.94 g/mol): C41.13; H6.44; N6.39.
ꢂ1
n
max (KBr), cm : 3543w, 3437w, 3142m, 3059w, 2955s,
3
3
2926s, 2901m, 2876m, 2810w, 2639w, 1717w, 1578vs, 1530vs,
1464s, 1452s, 1431s, 1406s, 1385s, 1329m, 1310w, 1259s, 1252vs,
1173m, 1150m, 1111s, 1076vs, 1040vs, 972m, 953m, 918w, 889m,
841vs, 795s, 770s, 750s, 706m, 675m, 658s, 623m, 542w, 496vw,
438vw, 384m.
C
22
H
IR
34
N
4
O
5
Si
2
(M ¼ 490.71 g/mol): C53.84; H6.98; N11.41.
ꢂ1
n
max (KBr), cm : 3420w, 2955s, 2932s, 2885m, 2544m,
2
372w, 2344w, 1921w, 1708vs, 1594s, 11457m, 1407s, 1295m,
254vs, 1210vs, 1168m, 1091vs, 1051s, 1008s, 967m, 839vs, 813s,
92s, 774s, 705m, 572m, 541m, 524w, 482w.
UVeVis (DMSO):
max ¼ 284 nm (ε ¼ 13480 mol Lcm );
max ¼ 454 nm (ε ¼ 284 mol Lcm ).
Fl (DMSO):
em ¼ 387 nm.
HNMR (CDCl ), , ppm: 0.05 (s, SieCH
Si), 1.63e1.71 (m, eCH e), 2.34e2.38 (m, eCH
and 8.88, 8.89 (d, aromatic H); intensity ratio: 3:1:1:1:2.
1
7
3. Results and discussion
ꢂ1
ꢂ1
l
ꢂ1
ꢂ1
l
The aim of this paper was to prepare metallopolymers by
incorporating metal in a supramolecular donor-acceptor structure
where 1,3-bis(3-carboxypropyl)tetramethyldisiloxane was used as
proton donor and 4,4 -azopyridine and imidazole as proton
acceptors. First, the supramolecular structure with 4,4 -azopyr-
l
1
3
d
3
), 0.54e0.58 (m, eCH
2
e
0
2
2
eCOOH), 7.77, 7.78
0
idine, 1, (Scheme 1a) was isolated and fully characterized. Self-
2
.3.2. Synthesis of the metallopolymer 2
The ethanolic ligand solution prepared just after the same recipe
and the same conditions as those described above was added to
a solution consisting of 0.3600 g (0.49 mmol) Co(ClO
assembling was proved by the presence of the FTIR absorption
bands around 1921 and 2544 cm specific for hydrogen bond [31]
ꢂ1
(Fig. 1Sb). The disappearance of the out-of-plane OH wagging
ꢂ1
4
)
2
ꢀ 6H
2
O
vibration band of the carboxylic acid dimer at 944 cm also indi-
dissolvedin 15 mL distilled waterand the mixturewas left to stand at
room temperature. A crystalline product separated after about two
weeks. Yield: 0.3 g, 27%. The compound is soluble in DMF, DMSO.
Elem. anal., %wt: Found, %: C46.1; H6.2; N6.9. Calcd. for
cates the involving of the carboxylic OH group in hydrogen bonds
with pyridyl groups [31] (Fig. 2S).
ꢂ1
The IR absorption bands
n
as(SieOeSi) 1051,1092 cm
s
; n (SieOe
ꢂ1
ꢂ1
ꢂ1
ꢂ1
Si) 541, 573, 619 cm
,
n
as(SiC
2
) 793 cm
;
n
s
(SiC
2
) 706 cm
;
n
(Sie
ꢂ1
ꢂ1
C
34
H57.4CoCl0.6
N
4
O
10Si
4
(M ¼ 874.80 g/mol): C46.7; H6.6; N6.4.
CH
3
) 1255 cm
;
n
as(CeH) 2955 cm
and 2885 cm
;
u
(CH
3
)
ꢂ1
ꢂ1
IR
n
max (KBr), cm : 528w, 548w, 573m, 592w, 625s, 667w,
840 cm indicate the presence of the dimethylsiloxane moiety in
0
710w, 746w, 793s, 843s, 887w, 1016s, 1049vs, 1088vs, 1111vs,
structure, while the 4,4 -azopyridine is manifested by the band at
Please cite this article in press as: Vlad A, et al., Metallopolymeric structures containing highly flexible siloxane sequence, Polymer (2012),
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4
A. Vlad et al. / Polymer xxx (2012) 1e11
CH3
Si
CH3
Si
O
O
O
H
n
+
n
N
N
N
N
N
O
H O
CH3
CH3
in refluxing ethanol
a
CH3
Si
CH3
Si
O
O
O
H
N
N
N
O
H O
CH3
CH3
n
1
+
n
Co(ClO4)2
b
2
Scheme 1. The stepwise synthesis pathway to the supramolecular polymer 1 and metallopolymer 2.
ꢂ1
1
410 cm assigned to a stretching vibration of the azo group that
this field as a result of the complex formation. One of them, that at
1
ꢂ1
appears as a single band [32]. In the H NMR (CDCl
3
) spectrum only
1105 cm , which in supramolecular polymer 1 can be seen at
ꢂ1
a very slight shift of the peaks to lower field was observed, sup-
porting the association by hydrogen bonding. In the next step,
cobalt(II) perchlorate was added to the ethanolic solution gener-
ating supramolecular 1 when an interesting rearrangement of the
supramolecular structure occurs with the insertion of the metal
1092 cm , may be assigned to an in-plane CH bending according
1
to Ref. [35] (Fig. 1Sc). In H NMR (DMSO) spectra there are present
the peaks at position and in intensities ratio according to the
presumed structure.
UVeVis spectrum of the compound 1 (Fig. 1, curve a) shows an
intense band at 282 nm and a low band at 456 nm both assigned to
(
Scheme 1b) due to the known ability of the carboxyl group to
0
coordinate metal ions; symmetrical 4,4 -azopyridine ligand is also
known as a versatile bridging ligand and has the potential to act as
a linking group between metal or metal cluster units [33]. The
metallopolymer 2 separated as brown crystalline compound.
In FTIR spectrum of the resulted metal-containing compound,
the band assigned to C]O stretching vibration from carboxyl
group at 1715 cm in free acid disappeared and two new bands
developed in 2 at 1549 cm and 1448 cm , assigned to
(COO ) vibration, respectively [34], as a result of the
involving carboxyl group in coordination with metal by forming
pep* transitions in the ligand [24]. Through metal inclusion in
compound 2, the band at 282 remains at about the same position,
while the second band red shifts slightly to a lower wavenumber,
regardless of the solvent nature, as a result of the metal-to-ligand
charge transfer (Fig. 1, curves b and c).
In another approach, imidazole was used as a co-ligand, along
with 1,3-bis(carboxypropyl)tetramethyldisiloxane, to prepare the
metallopolymer 4 (Scheme 2). Imidazoles that are known to coor-
dinate with the transition metals in a variety of biologically
important molecules can coordinate to the metal ion as a mono-
dentate or bidentate ligand [36]. First, the proper siloxane-
imidazole supramolecular polymer, 3 (Scheme 2a), was isolated
as a paste and characterized as such. The formation of the supra-
molecular structure was proved by the presence in FTIR spectrum
ꢂ1
ꢂ1
ꢂ1
ꢂ
n
as(COO )
ꢂ
and
n
s
metal carboxylate. The N]N group presence in structure is proved
by the band at 1420 cm [32]. The bands characteristic for the
bond from dimethylsiloxane moiety are very slightly shifted as
compared with those from free dicarboxylic acid and supramo-
ꢂ1
ꢂ1
lecular polymer, 1. The strong, sharp SieOeSi band situated at
of the absorption bands at 1967 and 2505e2583 cm character-
ꢂ1
1
073 cm in free acid overlapped with other bands developed in
istic for the presence of hydrogen bonding (Fig. 2Sb). A zinc salt,
zinc acetate monohydrate, Zn(OOCCH
3
)
2
ꢀ 2H
2
O, was chosen as
metal provider and the synthesis of the metallopolymer 4 has led in
an one-step reaction (Scheme 2a,b), without ligand isolation.
Product 4 separated from the reaction as a crystalline mass and
proved to contain moieties from all reactants. In the FTIR spectrum
ꢂ1
ꢂ1
for 4 (Fig. 2Sc), bands at 1578 cm and 1431 cm were assigned to
ꢂ
ꢂ
the
n
as(COO ) and
n
s
(COO ) vibrations, respectively [34], and only
ꢂ1
a very small band at 1717 cm assigned to residual free carboxyl
groups. The band at 1530 cm
ꢂ1
is assigned to imidazole ring
vibration. The siloxane presence is proved by the bands at
ꢂ1
ꢂ1
ꢂ1
1
n
076 cm for
n
as(SieOeSi), 1252 cm for
n
(SieCH
3
), 795 cm
ꢂ1
as(SiC2); 2955 cm for
n
as(CeH).
3.1. Structural characterization
0
The 1,3-bis(carboxypropyl)tetramethyldisiloxane and 4,4 -azo-
pyridine components of the crystal structure 1, are interacting
through a single intermolecular O1eH∙∙∙N1 hydrogen bond,
leading to the formation of a 1D supramolecular chain (see Fig. 2
along with atom labelling scheme). The main crystal packing
motif essentially results from the parallel packing of two-
dimensional supramolecular layers oriented along an ac
2 2
Fig. 1. UVeVis spectra for the prepared compounds: a-1 in CH Cl ; b-2 in DMF; c-2 in
DMSO.
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A. Vlad et al. / Polymer xxx (2012) 1e11
5
CH3
CH3
Si
O
O
O
H
Si
n
+
n
HN
N
O
H
CH3
CH3
O
methanol/water
RT
a
CH3
CH3
Si
O
O
O
H
Si
O
H
O
HN
N
CH3
CH3
n
3
+
n
Zn(CH COO) x 2H O
3 2
2
b
4
Scheme 2. The synthesis pathway to the metallopolymer 4.
crystallographic plane. Each layer (Fig. 3) is built from infinite
chains (Fig. 2) associated through a system of stacking inter-
action, which are evidenced by short centroid to centroid distances
4.0 Å) between the centrosimmetrically related pyridine rings of
donor with MOF via H-bonds towards two carboxylate groups
coordinated to adjacent Co atoms. One of carboxylate group is
pep
1
1
ii
coordinated in
h :h mode to Co atom, whereas the other one,
i
1
1
(
bridging Co1 and Co1 atoms, is coordinated in
h
:h
:
m
2
mode. Each
adjacent 1D chains.
Co atom has a slightly distorted octahedral O
4
N
2
environment
0
A view of the asymmetric part of the unit cell in crystal structure
being coordinated by two 4,4 -azopyridine as monodentate ligands,
one bidentate and two symmetrically related bidentate-bridging
carboxylate ligands. Cobalt oxidation states are consistent with
charge balance and CoeO, CoeN bond parameters (see Fig. 4)
2
is shown in Fig. 4.
Selected bonds lengths (Å) and angles ( ) for coordination site:
Co1-O1 2.199(3), Co1-O2 2.177(3), Co1-O3 2.002(3), Co1-O4i
.009(3), Co1-N1 2.176(3), Co1-N4 2.182(3), Si1-O5 1.642(4); O3-
ꢁ
i
ii
i
ii
2
[37,38]. Co1,,,Co1 , Co,,,Co1 and Co ,,,Co1 separation within
two-dimensional network are equal to 4.005(1), 17.897(1) and
14.246(1) (Å), respectively. A view of 2D coordination network
showing the outward positions of non-coordineted 1,3-
bis(carboxypropyl)tetramethyldisiloxane is shown in Fig. 6.
The presence of the chlorine atoms with partial SOF (0.2 or 0.1)
can be explained by the presence of the traces of (2,6-dichloro)-
i
i
Co1-O4 118.9(1), O3-Co1-N1 87.7(1), O4 -Co1-N1 87.7(1), N1-Co1-
i
O2 92.0(1), O3-Co1-N4 91.3(1), O4 -Co1-N4 95.0(1), O2-Co1-N4
8
7.7(1), N1-Co1-O1 86.5(1), O2-Co1-O1 59.2(1), N4-Co1-O1 91.0(1).
Single crystal X-ray diffraction analysis reveals that compound 2
comprises two-dimensional coordination network constructed
from CoN
2
O
4
sites linked through 1,3-bis(carboxypropyl)tetrame-
0
0
thyldisiloxane and 4,4 -azopyridine spacer as bridging ligands. As
can be seen from Figs. 4 and 5, 1,3-bis(carboxypropyl)tetrame-
thyldisiloxane exhibits different structural functions. One of them
acts as double-deprotonated bidentate-bridging ligand, while the
second, in molecular form, is non-coordinated being associated as
4,4 -azopyridine that inherently is formed as secondary product
during oxidation of aminopyridines by sodium hypochlorite
[24,25], as literature already reported [39].
The crystal structure 4 is built from 1D coordination polymer. Its
structure along with the atom labelling scheme is shown in Fig. 7.
The Zn atom has a tetrahedral coordination provided by three
oxygen atoms from carboxylate groups and one nitrogen atom from
imidazole as monodentate ligand. One of the carboxylate groups
fulfils a bidentate-bridging function, while the second is mono-
coordinated, the second oxygen atom being involved as acceptor
into intermolecular NeH∙∙∙O hydrogen bond towards imidazole
Fig. 2. The view of H-bonded 1D chain in crystal structure 1. Non-relevant hydrogen
atoms are omitted for clarity. Thermal ellipsoids are drawn at 50% probability level.
Intermolecular H-bond O1eH∙∙∙N1 [O1eH 0.82 Å, H∙∙∙N1 1.88 Å, O1∙∙∙N1 2.679(3)
ꢁ
Å, O1eH∙∙N1 165.6 ] are also shown. Symmetry codes: i)1=2 ꢂ x; 3=2 ꢂ y; 3 ꢂ z;
ii)1 ꢂ x; y; 1=2 ꢂ z.
Fig. 3. 2D supramolecular layer in crystal structure 1.
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6
A. Vlad et al. / Polymer xxx (2012) 1e11
ligand of adjacent polymer chain. The crystal structure of 4 is
constructed from the packing of two-dimensional supramolecular
layers, consolidated via a system of above mentioned H-bonds, as
shown in Fig. 8.
3.2. Thermal behaviour
The thermal stability of the metallopolymers was evaluated by
thermogravimetric analysis performed in inert atmosphere. The
TG-DTG curves for the two polymers are presented in Fig. 9. As
shown, polymer 2 suddenly decomposes in a very narrow single
ꢁ
stage (Tpeak ¼ 271.5 C) with a weigh loss of 68 %wt. In the case of 4,
the decomposition occurs in three steps as can be seen in Table 2. It
ꢁ
could be presumed that in the first step (Tpeak ¼ 148 C), the water
traces sorbed during handling the sample in normal atmosphere
conditions are removed. The main weight loss (27.33 %wt.) occurs
in the second step which in fact included two processes, at 282.1
ꢁ
and 296.7 C. However, the decomposition process is not complete
ꢁ
at 900 C, the trend of the curves being decreasing for both samples
at this temperature. Results of the elemental analysis performed by
EDX for the TGA residues (Table 2) reveal the presence of all
elements (except H, which can not be observed) that are listed in
Table 1. FTIR spectra of these residues reveal that the characteristic
bands for CeH bond are still present. In the spectrum of the
compound 4, for example, valence vibrations,
gas(CeH) at
ꢂ1
ꢂ1
2
954 cm and
g
s
(CeH) at 2854 cm , and deformation vibrations,
ꢂ1
d(CH
2
) at 1462, 1371, and 1304 cm [40] can be seen (Fig. 3S).
ꢂ1
ꢂ1
Absorption bands at 1069 cm and around 797 cm assigned to
g
ꢂ1
as,s(SieO) in SiO
2
and at 469 cm assigned to
d
(SiO
2
) [41] co-exist
ꢂ1
with a shoulder at about 1040 cm assigned to SieOeSi groups
from initial compound. The band at 1256 cm and the shoulder at
ꢂ1
ꢂ1
769 cm are assigned to valence vibrations
g(SiC) [42]. The valence
ꢂ1
vibration
g(ZnO) is found as a shoulder at 412 cm [43]. FTIR
spectrum of the compound 2 shows a similar pattern with small
ꢂ1
differences in 400e700 cm range. Our explanation for the pres-
ꢁ
Fig. 4. View of the asymmetric part of the unit cell in crystal structure 2. Thermal
ellipsoids are drawn at 50% probability level. Minor component of disordered non-
coordinated 1,3-bis(carboxypropyl)tetramethyldisiloxane, non-relevant H-atoms, as
well as the chloride atoms with partial SOF are not shown for clarity. Symmetry codes:
i)ꢂx; 1 ꢂ y; 1 ꢂ z; ii)1 þ x; 1 þ y; z.
ence of the organic part even at 900 C is that oxides (e.g. SiO or
2
ZnO), formed in the first decomposition step, insulate the rest of the
material thus delaying its complete decomposition. The residues,
which look like very porous materials, adsorb water as FTIR spectra
reveal by the presence of a broad and intense band centered at 3447
and 3425 for compounds 2 and 4, respectively, assigned to
Fig. 5. 2D coordination network in crystal structure 2. Non-coordinated 1,3-bis(carboxypropyl)tetramethyldisiloxane and methyl groups of the siloxane fragments are omitted for
clarity. Symmetry codes: i)ꢂx; 1 ꢂ y; 1 ꢂ z; ii)ꢂx ꢂ 1; ꢂy; 1 ꢂ z.
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A. Vlad et al. / Polymer xxx (2012) 1e11
7
symmetric and asymmetric vibrations of water molecules forming
ꢂ1
hydrogen bonds. The band at 1632 cm in the compound 2 and
ꢂ1
1
618e1637 cm in the compound 4 corresponds to deformation
2
vibrations of the water molecules, d(H O) [34].
Besides thermostability, other thermal properties, such as glass
transition temperatures or melt temperatures, dominate the
macroscopic properties of the material [44]. Therefore, thermal
behaviour of the obtained metallopolymers was also studied by
DSC, the recorded curves being presented in Fig. 10. Both
ꢁ
ꢁ
C
compounds show glass transition at 76 C (sample 2) and 7
sample 4) in the second or third scan. The glass transition is
(
characteristic for amorphous polymers or for the amorphous frac-
tion of a crystalline polymer. In our case, the investigated samples
were crystalline. More, these were separated as single-crystals and
investigated as such. It is presumed that the amorphous fraction in
the crystalline sample is generated as a result of the first heating
run when the sample melts and, by cooling in the second run, in the
absence of any solvent, it cannot reach the initial organization
degree. Instead, the presence of this transition is a proof for the
polymeric nature because, as it is known, at this temperature,
portions of the molecules begin to move and the polymer passes
from a glassy state to a rubbery state. Compound 2 shows a melting
ꢁ
transition at 125 C in the first heating that is nonreproducible in
subsequent runs; here the glass transition is evidently due to
ꢁ
development of amorphous phase. A melting transition at 137
C
was found in the case of the compound 4 in the first heating run, as
ꢁ
well as in subsequent runs (132 C). This would be explained by
a good organization of the material during cooling and justifies the
poor visibility of the glass transition.
3.3. Dynamic water vapour sorption analysis
The moisture sorption in polymer is very important for a variety
of industries ranging from microelectronics to adhesives and coat-
ings [45]. In order to study the behaviour of the crystalline supra-
molecular compounds in the presence of the humidity, the
sorptionedesorption isotherms were registered in dynamic
ꢁ
regime. The samples were dried at 25 C in flowing nitrogen
(250 mL/min) until the constant weight at RH <1%. Then, the relative
humidity (RH) was gradual 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. When RH decreased, the desorption curves were regis-
tered. The obtained isotherms at room temperature are presented in
Fig. 11.
Fig. 6. View of 2D layer along [110] crystallographic axis for compound 2. H-bonds
parameters: O6eH∙∙∙O1 [O6eH 0.82 Å, H∙∙∙O1 1.92 Å, O6∙∙∙O 1 2.715(6) Å, O6e
ꢁ
H∙∙O1
164.5 ];
O8eH∙∙∙O2
[O8eH
0.84
Å,
H∙∙∙O2
2.00
Å,
ꢁ
O8∙∙∙O2(1 ꢂ x; 1 ꢂ y; 1 ꢂ z) 2.700(7) Å, O8eH∙∙O2 139.6 ].
ꢁ
Fig. 7. 1D coordination polymer in crystal structure 4. Symmetry codes: i)x; 1=2 ꢂ y; z þ 1=2; ii)x; 1=2 ꢂ y; 1=2 þ z. Selected bonds lengths (Å) and angles ( ): Zn1-O11.974(3), Zn1-O4
i
i
1
.986(4), Zn1-O5 1.991(4), Zn1-N1 2.023(4), Si1-O3 1.632(4), Si2-O3 1.632(4); O1-Zn1-O4 131.9(2), O1-Zn1-O5i 109.9(2), O4-Zn1-O5 100.4(2), O1-Zn1-N1 105.5(2), O4-Zn1-N1
i
1
05.1(2), O5 -Zn1-N1 99.8(2).
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8
A. Vlad et al. / Polymer xxx (2012) 1e11
Fig. 8. Association of 1D polymer chains into two-dimensional layer in crystal structure 4. H-bonds parameters: N2eH∙∙∙O2 [n2eH 0.86 Å, H∙∙∙O2 1.893 Å, N2∙∙∙O 2 2.685(6) Å,
ꢁ
N2eH∙∙O2 167.3 ].
The isotherms for the two metallopolymers, 2 and 4, can be
assimilated as isotherms of type III according to Brunauer et al.
46,47], indicating that the results should not be described in terms
of free and bound water and of hydration layers. Both sorption
values and the isotherm shape indicate a hydrophobic material. The
hydrophobic character is conferred in principal by the presence of
and the hygroscopicity of the compounds increase due to the
raising temperature [49,50]. Also, the polar sites responsible for
water sorption either exist, or are progressively uncovered due to
the disorganization of the crystals as the temperature increases, or
they are created by dissociation of the hydrogen bonds [51]. This
process intensifies by temperature increasing, favouring the
molecular transport. It is important to highlight that, after sorption/
desorption cycle, both samples return exactly to the initial masses,
this proving the moisture stability of the compounds.
[
1
,3-bis(propyl)tetramethyldisiloxane moiety. Very low value was
obtained for the water sorption capacity in the case of 4, this being
of 2.6% at room temperature. The higher value, 8.3%, in the case of 2,
could be explained by the presence of free, non-coordinated
carboxylic groups as crystallographic data revealed (Fig. 4). The
isotherms show slight hysteresis over the entire humidity range. A
slight increasing of sorption capacity at 10.5 and 3.4% for 2 and 4,
respectively, occurs by temperature rising, as can be seen in the
Fig. 11. Although, as is known, sorption processes are generally
exothermic [48,49], it could be several causes for this somewhat
unexpected behaviour. The diffusion rate of the water molecules
3.4. Magnetic properties
1
The result of the magnetic measurements performed by H NMR
at 400 MHz, for the metallopolymer 2 in solution at room
temperature by applying Evans method [26e28] consist of
(
m
ef
)
atom ¼ 4.48 ꢃ 0.34 BM. This value is in the limits of the
2
þ
h
experimental data for Co in high spin state and O symmetry
Fig. 9. TGA (left axis, red line) and DTG (right axis, blue line) curves for the prepared samples 2 and 4. (For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)
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A. Vlad et al. / Polymer xxx (2012) 1e11
9
Table 2
The main thermogravimetrical parameters.
a
b
c
The residue amount at 900 ꢁC, % (composition, wt.%d)
Sample
Stage of thermal degradation
T
onset
T
peak
T
endset
Weight loss, %
2
4
I
I
97
121
180
272
148
282
274
160
303
68.0
1.99
27.33
23.62 (C33.96, N2.59, O42.16, Si16.67, Cl0.43, Co4.19)
56.09 (C47.76, N6.38, O18.47, Si16.06, Zn11.46)
II, III
297
IV
363
466
581
12.00
a
T
T
T
onsetethe temperature at which the thermal degradation begins.
peakethe temperature at which the degradation rate reaches its maximum value.
endsetethe temperature at which the process ends.
b
c
d
without hydrogen as determined by EDX.
[
52], which is in agreement with above presented crystallographic
insulating barriers, as XRD structural data revealed, could be
a reason for this behaviour.
data.
When the frequency is increased, the dipoles, which orient
themselves in the direction of the applied field, can no longer rotate
rapidly enough so that their oscillations begin to lag behind the
field which explains the observed decrease in the dielectric
constant with frequency [56]. The reduction of the dielectric loss
determined by frequency is attributed mainly to one of the two
components of it (the resistive loss and relaxation loss of the
dipole), namely to resistive loss. In this mechanism, the energy is
consumed by the mobile carriers within the sample. In high
frequency region, these carriers become immobile and thus, their
contribution to the energy consumption reduces [56]. The study
revealed the increases of both parameters determined by rising
temperature in the explored range (Figs. 4Se6S). The increase of
the conductivity with temperature (Fig. 4S) is explained by
increasing charge mobility [57]. This increasing is more evidently in
the case of the compound 4 with glass transition, as detected by
3
.5. Dielectric measurements
It would be expected that the metal presence in the polymer
structures would give some interesting properties, especially
electrophysical ones. The metal ion presence in the polymer may
favour the appearance of electroconductivity, although almost all of
the metal-containing polymers are insulators [53] or operate in the
ꢂ8
ꢂ1
range of semiconductors (
s
¼ 10 e1 S cm ) [8]. This is due to the
problems associated with matching the orbital energies of the
conjugated organic components and metal centers [8]. However,
there are still sufficient reasons for taking into account their elec-
trical properties. One of them is the ability of the metal to reversibly
bind additional ligands resulting in a very sensitive modification of
the conductivity of the system due to alteration of the energy levels
of the metal-based orbitals. This would be the basis for a sensing
mechanism to detect gaseous molecules. Small molecules, often
ꢁ
DSC, at 7 C. Therefore, around this value, a significant increasing in
the conductivity values can be observed, more pronounced at low
frequencies (Fig. 4S). The dielectric parameters (permittivity and
loss) values also more abruptly increase as the temperature
approaches the glassy transition value (see Fig. 5S and 6S).
analytes, for example a gas, CO
ligands [8].
The dielectric responses in dependence on frequency and
temperature were studied by using dielectric spectroscopy for the
two metallopolymeric structures reported in this paper. Variation
of these parameters with frequency at room temperature is pre-
2
, CO, NO, etc. can be additional
3.6. Luminescence properties investigation
sented in Fig. 12. Ac conductivity derived from these data as
s
ac ¼ ε
0
u
ε” (where ε
0
is the permittivity of free space, ε” is the dielectric
A special interest in metallopolymers consists in their photo-
physical properties. Therefore, the emission spectra were recorded
for the two ligands and derived metallopolymers. The polymer 1
exhibits any emission band, neither in solution nor in solid state,
while the metallopolymer 2 shows a weak emission at 410 nm upon
340 nm excitation as a result of the re-organization of the supra-
molecular structures by metal coordination insertion in the main
chain beside azopyridine.
loss and
u is the angular frequency) [54,55]) is also plotted. As it can
be seen, while the dielectric parameters, permittivity and loss,
decrease, the conductivity increases by frequency increasing.
Almost linear conductivity-frequency dependence is an indication
for hopping type conduction [56]. However, the values of the
conductivity so determined are situated at the bottom of the
semiconductor field. The existence of the interchain siloxane
Fig. 10. DSC curves for the samples 2 and 4.
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A. Vlad et al. / Polymer xxx (2012) 1e11
Fig. 11. The shapes of the moisture sorptionedesorption isotherms for the samples 2
and 4 at 25 C and 35 C.
ꢁ
ꢁ
Fig. 13. Emission spectra of the compound 3 in DMSO under different excitations: a-
300 nm; b-320 nm; c-330 nm; d-340 nm; e-350 nm.
It is generally known that in the metallopolymers, the role of the
metal ion has been predominately as a linker, the optical properties
being derived from the linkages between the metal centers [1]. In
our case, the most emissive component is imidazole from the
structures 3 and 4. Thus, the fluorescence spectrum of the
compound 3 in dimethyl sulfoxide (DMSO) reveals an emission
maximum at about 392 nm when the solution was excited with
3
20 nm light. With the increase of excitation wavelength, the
emission spectra of 3 exhibits a red shift and the emission intensity
decreases gradually with increasing excitation wavelength (Fig. 13).
The highest emission intensity was observed under excitation at
3
20e330 nm. The shift of emission maximum to longer wave-
lengths can be assigned to a strong correspondence between the
excitation energy and the vibronic structure of the fluorescence
spectra [58].
A fluorescence band at 393 nm was evidenced for 3 in solid
state when the excitation wavelength was set at 320 nm (Fig. 14).
This emission band was practically independent by the excitation
wavelength probably due to the presence of only one type of
fluorophore in the system. This difference between the behaviour
in solid state and solution comes from the fact that, in a polar
solvent such as DMSO, this competes in the formation of the
hydrogen bonds with the two components of the supramolecular
polymer.
Fig. 14. Emission spectra for: ae3 and be4 in solid state.
0
00
Fig. 12. Frequency dependence of the ac conductivity
s
ac, dielectric constant ε and dielectric loss ε in metallopolymers: ae2 and be4 at room temperature.
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A. Vlad et al. / Polymer xxx (2012) 1e11
11
Polymer 4 displays a strong emission at about 387 nm in solid
state upon 320 nm excitation (Fig. 14) due to the conformational
rigidity of the structure by the coordination effect of carboxylic
groups of siloxane component to Zn(II) ions which contribute to the
decrease of the nonradiative decay of intraligand emission [59,60].
Such a polymer would be of interest in electroluminescent devices.
[11] Grimm F, Ulm N, Grçhn F, During J, Hirsch A. Chem Eur J 2011;17:9478e88.
[
[
[
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Two metallopolymeric structures containing highly flexible
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Appendix A. Supplementary data
Supplementary data related to this article can be found online at
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Please cite this article in press as: Vlad A, et al., Metallopolymeric structures containing highly flexible siloxane sequence, Polymer (2012),
http://dx.doi.org/10.1016/j.polymer.2012.11.021