Solid state irreversible anion-exchange on one-dimensional silver(I) coordination polymer nanostructures

Article abstract of DOI:10.1016/j.ica.2011.12.032

A new one-dimensional silver(I) coordination polymer [Ag(μ-bpfb)(NO ₃)]_n (1), bpfb = N,N′-bis(4-pyridylformamide)-1,4- benzene, has been synthesized and characterized by IR, NMR spectroscopy and single crystal X-ray crystallography. Nanorods compound 1 were obtained by sonochemical process and characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The nitrate ions of compound 1 in nanostructure exchange with perchlorate, thiocyanate and azide anions by the solid state reaction. Three new compounds [Ag(μ-bpfb)(ClO₄)] _n (2), [Ag(μ-bpfb)(SCN)]_n (3) and [Ag(μ-bpfb)(N ₃)]_n (4), were characterized by IR spectroscopy, X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The silver nanoparticles were obtained from direct calcination of compounds 1-4 nanostructures in an electrical furnace at 673 K.

Full text of DOI:10.1016/j.ica.2011.12.032

Inorganica Chimica Acta 382 (2012) 171–176
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Inorganica Chimica Acta
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Note
Solid state irreversible anion-exchange on one-dimensional silver(I)
coordination polymer nanostructures
⇑
Zohreh Rashidi Ranjbar, Ali Morsali
Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
A new one-dimensional silver(I) coordination polymer [Ag(l
-bpfb)(NO3)]n (1), bpfb = N,N0-bis(4-pyridyl-
Article history:
Received 15 November 2010
Received in revised form 14 December 2011
Accepted 17 December 2011
Available online 24 December 2011
formamide)-1,4-benzene, has been synthesized and characterized by IR, NMR spectroscopy and single
crystal X-ray crystallography. Nanorods compound 1 were obtained by sonochemical process and char-
acterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The nitrate ions of
compound 1 in nanostructure exchange with perchlorate, thiocyanate and azide anions by the solid state
reaction. Three new compounds [Ag(l-bpfb)(ClO4)]n (2), [Ag(l-bpfb)(SCN)]n (3) and [Ag(l-bpfb)(N3)]n
Keywords:
(4), were characterized by IR spectroscopy, X-ray powder diffraction (XRD) and scanning electron micros-
copy (SEM). The silver nanoparticles were obtained from direct calcination of compounds 1–4 nanostruc-
tures in an electrical furnace at 673 K.
Anion exchange
Solid state reaction
Silver
Ó 2011 Elsevier B.V. All rights reserved.
Nanoparticle
1. Introduction
2. Experimental
Coordination polymer is a general term used to indicate an
infinite array composed of metal ions and organic moiety as bridging
and linker ligands. The central metallic atoms and organic ligands
are two important operatives in design and construction of desirable
frameworks [1–3]. The coordination polymers convert into supra-
molecular aggregates via self-assembly by non-covalent interac-
tions [4–7]. These huge intriguing structures have gained chemists
interest because of their unique potential applicability as functional
materials in many areas such as storage, exchange, and catalysis
[8–13]. Anion exchange is an important property of coordination
polymers and it has attracted increasing attention in recent years.
Any network with cationic metals as center ion would include free
counter anions in the channels or pore and could be applied as the
anion-exchange materials [14,15]. The trapped anions in the cavity
can be exchanged with different anions [16–18]. Ion exchange has
been observed in solution phase in most cases but ion exchange in
solid-state would be observed, too [19–21]. During this decade;
the simplicity, low cost, high output and low pollution are the rea-
sons for developing the solid-state reaction [22–26]. The coordina-
All reagents for the synthesis and analysis were commercially
available and used as received. Melting points were measured on
an Electrothermal 9100 apparatus. IR spectra were recorded using
Perkin–Elmer 597 and Nicolet 510P spectrophotometers. Crystallo-
graphic measurements were made using
area-detector diffractometer. The intensity data were collected
using graphite monochromated Mo K radiation. The structure
a
Bruker APEX
a
was solved by direct methods and refined by full-matrix least-
squares techniques on F2. X-ray powder diffraction (XRD) measure-
ments were performed using an X’pert diffractometer of Philips
Company with monochromated Cu ka radiation. The samples were
characterized with a scanning electron microscope with gold
coating.
2.1. Synthesis of N,N0-bis(4-pyridyl formamide)-1,4-benzene (bpfb)
At room temperature, 1 g (9.2 mmol) of 1,4-phenylenediamine
(bpfb) was dissolved in 50 ml of dry THF. To this solution was
added 5 g of the commercially available hydrochloride salt of isoni-
cotinoyl chloride. After stirring for 30 min, 10 ml of triethylamine
was added and the mixture was stirred overnight. After evapora-
tion to dryness, the yellow residue was poured into an aqueous
solution (50 ml) of Na2CO3 (1.2 M) and then the product filtered.
The precipitant was washed with distilled water and yellowish
powder was obtained after drying at ambient temperature ca.
75% yield [27].
tion polymer [Ag(l-bpfb)(NO3)]n (1) has been synthesized as bulk
and nano-size. Both obtained nanorods and bulk form were used
as reagents for anion exchange reactions in solid state. The obtained
products from anion replacement are [Ag(
l-bpfb)(ClO4)]n (2), [Ag
(l
-bpfb)(SCN)]n (3) and [Ag( -bpfb)(N3)]n (4) nanostructures. The
l
compounds 1–4 were calcinated at 673 K and the silver nanoparti-
cles were obtained after decomposition.
⇑
IR (cmꢀ1) selected bands: 3340(s), 3025(s), 1646(s), 1542(w),
1443(br), 1407(w), 1314(w), 840(w), 661(w).
Corresponding author. Tel.: +98 21 8011001; fax: +98 21 8009730.
E-mail address: morsali_a@modares.ac.ir (A. Morsali).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.12.032

172
Z.R. Ranjbar, A. Morsali / Inorganica Chimica Acta 382 (2012) 171–176
1H NMR (DMSO, d): 10.54 (s, 2H, NH); 8.77 (d, 4H, H-py); 7.87
(d, 4H, H-Py); 7.78 (s, 4H, H-Ar) ppm.
(b) The 0.2 g nanorods of compound 1 and the excess quantities
of KSCN as solids were added to each other and grinded for one
hour. The nano-structure of compound 4 were washed with etha-
nol and subsequently dried at air atmosphere.
2.2. Synthesis of [Ag(l-bpfb)(NO3)]n (1)
IR (cmꢀ1) selected bands: 3340(s), 3025(s), 2143(s), 2100(s),
1656(s), 1555(w), 1513(br), 1415(w), 840(w), 661(w), 522(w).
(c) The 0.2 g nanorods of compound 1 and the excess amount of
NaN3 were grinded for one hour in solid-phase. The nano-struc-
tures of compound 3 were washed with ethanol and subsequently
dried at air atmosphere.
The N,N0-bis(4-pyridylformamide)-1,4-benzene (bpfb) (0.159 g,
0.50 mmol) was dissolved in DMF (5 mL) and this solution poured
into a test tube. An equal amount (1:1) mixture of DMF and aceto-
nitrile (5 mL) was layered on top of bpfb solution; then a solution
of AgNO3 (0.085 g, 0.5 mmol) in acetonitrile (5 mL) carefully added
on top of the mesosphere layer without its disturbing. The gray sin-
gle crystals were obtained after a month in mesosphere layer, d.p.
>300 °C.
IR (cmꢀ1) selected bands: 3340(s), 3025(s), 2029(s), 1656(s),
1555(w), 1513(br), 1415(w), 840(w), 661(w), 522(w).
IR (cmꢀ1) selected bands: 3340(s), 3025(s), 1656(s), 1555(w),
1513(br), 1415(w), 1340(w), 1310(s), 840(w), 661(w), 522(w).
Anal. Calc. for C18H14AgN5O5: C, 22.1; H, 2.87; N, 14.35. Found: C,
21.8; H, 2.91; N, 14.13%.
2.5. Synthesis of silver nanoparticles by direct thermal decomposition
of compounds 1–4
The 0.1 g precipitate of compound 1–4 was calcinated at
673.15 K in an electrical furnace at static air atmosphere for 2 h.
By this process, the gray silver nanoparticles were obtained.
1H NMR (DMSO, d): 10.51 (s, 2H, NH); 8.78 (d, 4H, H-py); 7.86
(d, 4H, H-Py); 7.77 (s, 4H, H-Ar) ppm.
13C NMR (DMSO, d):163.6, 150.2, 141.9, 134.7, 121.5, 120.8 ppm.
2.3. Synthesis of [Ag(l-bpfb)(NO3)]n (1) nanorods by sonochemical
process
To prepare the nanorods of compound 1 by sonochemical process
was used ultrasonic bath (138 W) for 1 h. A proper volume, 30 mL
acetonitrilic solution of AgNO3 (0.3 mmol, 0.05 g) was poured into
30 mL prepared solution of ligand (bpfb) in DMF (0.3 mmol,
0.095 g), under the ultrasonic irradiation. The obtained precipitates
were filtered, subsequently washed with ethanol and then dried,
d.p. >300 °C.
IR (cmꢀ1) selected bands: 3340(s), 3025(s), 1656(s), 1555(w),
1513(br), 1415(w), 1340(w), 1310(s), 840(w), 661(w), 522(w).
1H NMR (DMSO, d): 10.51 (s, 2H, NH); 8.78 (d, 4H, H-py); 7.86
(d, 4H, H-Py); 7.77 (s, 4H, H-Ar) ppm.
13C NMR (DMSO, d):163.6, 150.2, 141.9, 134.7, 121.5, 120.8 ppm.
2.4. Synthesis of nano-structure [Ag(
SCNꢀ) from nano-rods of [Ag(
-bpfb)(NO3)]n (1) by solid-state reaction
l
-bpfb)(X)]n (Xꢀ = ClO4ꢀ, N3ꢀ and
l
(a) The obtained percipitate (0.2 g) nanorods of compound 1
and the excess amount of NaClO4 were added to each other and
grinded for one hour. The nano-structure of compound 2 was
washed with ethanol, subsequently dried at air atmosphere.
IR (cmꢀ1) selected bands: 3340(s), 3025(s), 1656(s), 1555(w),
1513(br), 1415(w), 1083(s), 840(w), 661(w), 522(w).
Scheme 1. Showing of preparation of nanostructure compounds 2–4 from nano-
structure [Ag(
l-bpfb)(NO3)]n (1) and preparation of silver nanoparticles from
Fig. 1. The IR spectra of compound (a) [Ag(
l-bpfb)(NO3)]n (1); (b)
calcination of compounds 1–4.
[Ag( -bpfb)(ClO4)]n (2); (c) [Ag( -bpfb)(SCN)]n (3); and (d) [Ag(l
l
l
-bpfb)(N3)]n (4).

Z.R. Ranjbar, A. Morsali / Inorganica Chimica Acta 382 (2012) 171–176
173
are connected by covalent bonds to two nitrogen atoms (N1, N20)
of pyridyl groups of bpfb ligand in one direction. Therefore, this
polymer grows in one dimension along c crystallographic axis
(Fig. 2a). The chains were connected by hydrogen bonds. So, these
connections cause the structure grows in second dimension and
the sheets form. Two distinct oxygen atoms (O1s, O2s) of nitrate
groups connect to the hydrogen atoms of amidic groups (N–HꢁꢁꢁO)
3. Results and discussion
The single crystals of [Ag(l-bpfb)(NO3)]n (1) have been prepared
by diffusion method. This compound was obtained as bulk powder
by direct adding the reagents solution to each other. Compound 1
has been synthesized as nanostructure by sonochemical method.
Nanorods of compound 1 have been used as precursor for synthesis
in the ligand structure (Fig. 2b). The sheets connect by p–p stack-
of compound [Ag(l-bpfb)(ClO4)]n (2), [Ag(l-bpfb)(SCN)]n (3) and
ing interactions and the structure grows as three-dimensional
supermolecule (Fig. 2c).
[Ag(l-bpfb)(N3)]n (4) as nanostructure in solid state. After heating
-bpfb)(X)]n (Xꢀ = ClO4
,
ꢀ
all the synthesized nanostructures, [Ag(
l
SCNꢀ, N3ꢀ), at 673 K, silver nanoparticles were obtained (Scheme 1).
The IR spectra of compound 1 at nano-size and bulk form show
the absorption bands at around 3025 cmꢀ1 are corresponding to
the C–H modes of the aromatic rings of ligand bpfb. The variable
intensity absorption bands in the frequency range 1400–
1580 cmꢀ1 are corresponding to ring vibrations of the ‘‘py’’ ring.
Decomposition behavior of compound (1) was investigated in
static air atmosphere from ambient temperature to 700 °C (Fig. 8).
Crystal form and nanostructure of the compound (1) have various
thermal stabilities. The crystal form of the compound (1) is stable
up to 320 °C and nanostructure to 180 °C at which temperatures
the organic coordinated ligand exit (calc: 65.22%, obs: 60.81%). So,
this point shows that compound 1 in nano form is less stable than
in the bulk form. The experimental mass loss of 20.78% is consistent
with the calculated value of 12.7% for the elimination of one mole-
cule of NO3. After nitrate molecule leaves the residue, gray powder
would be silver metal (calc: 22.095%, observed: 22.12%). Two frag-
ments exit during two exothermic processes (Fig. 8).
Fig. 3a, b show X-ray powder diffraction (XRD) patterns of the
simulated X-ray crystallography data and bulk form of compound
1. Good matches were observed between the patterns of simulated
X-ray crystallography data and the X-ray powder diffraction in
bulk form and nano-size of compound 1.
The characteristic bands of the nitrate anion appear at 1335 cmꢀ1
The broad absorption band at 3340 cmꢀ1 is assigned to the
(NH)
.
m
modes (Fig. 1). The 1HNMR spectrum shows a broad signal at
10.51 ppm assigned to the NH protons. In aromatic region, two dou-
blet bands have been observed at 8.78 and 7.86 that assigned to
protons of the pyridine rings and one singlet signal at 7.77 ppm as-
signed to four protons of middle aromatic ring. The 13C NMR spec-
trum shows six distinct signals, 163.6, 150.2, 141.9, 134.7, 121.5,
120.8 ppm, assigned to aromatic carbon atoms of bpfb ligand.
Also, the structure of compound 1 was determined by X-ray
crystallography. The X-ray crystallography data shows Ag(I) atoms
Fig. 2. Showing (a) a fragment of the one-dimensional chain in compound 1 along crystallographic c axis [001]; (b) hydrogen bonds form the 2D coordination polymer; and
(c) The stacking interaction in supermolecule structure (Ag = violet, O = red, C = gray, N = blue). (For interpretation of the references in color in this figure legend, the
reader is referred to the web version of this article.)
p–p

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Fig. 3. The XRD patterns of (a) simulated from single crystal X-ray data of
compound 1; (b) bulk form and nono-size as synthesized of compound 1; (c) nano-
structure of compound 2; (d) nanostructure of compound 3; and (e) nanostructure
of compound 4.
The nanorods of compound 1 were synthesized at ultrasound
irradiation with the power of 138 W and characterized by IR spec-
troscopy, X-ray powder diffraction and Scanning Electron Micros-
copy. The IR spectroscopy data and XRD pattern of compound 1
nanorods are as the same as the IR spectroscopy data and XRD
pattern of single crystal and bulk form (Figs. 1a and 3b). The
nanostructure of compound 1 has been shown by Scanning Elec-
tron Microscopy (Fig. 4a). The nano-rods of compound 1 were used
as precursor to prepare the nano-structures of compounds 2, 3 and
4. After grinding the compound 1 with NaClO4, KSCN and NaN3 in
solid phase, nano-structures of compounds 2, 3 and 4 were
obtained. The IR spectra of compounds 2, 3 and 4 show the absorp-
tion bands of the C–H modes of the aromatic rings, the vibrations
of the ‘‘py’’ ring and (NH) modes. These visible bands are as the
same as the observed bands in the IR spectrum of compound 1.
But, the band at 1335 cmꢀ1 of the nitrate anion completely disap-
pears in the spectrum of compounds 2, 3 and 4. The absorption
band at 1083 cmꢀ1 is assigned to the perchlorate anion vibration
mode in the IR spectrum of compound 2 (Fig. 1b) and the absorp-
tion band at 2100 cmꢀ1 in the compound 3 is assigned to the thio-
cyanate anion vibration mode (Fig. 1c). Also, the absorption band at
2029 cmꢀ1 is assigned to the azide anion vibration mode in the
compounds 4 (Fig. 1d). The nano-structures of compounds 1–4
have different XRD patterns (Fig. 3). Acceptable matches, with
Fig. 4. The SEM images of compound (a) [Ag(
l
-bpfb)(NO3)]n (1); (b) [Ag(
l-
bpfb)(ClO4)]n (2); (c) [Ag(
l-bpfb)(SCN)]n (3); and (d) [Ag( -bpfb)(N3)]n (4)
l
nanostructures.
slight different in 2h, were observed between the simulated from
single-crystal X-ray data patterns and those from the experimental

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175
Fig. 5. XRD pattern of silver nanoparticles produced by calcinations of compounds
1–4.
powder X-ray diffraction patterns of single-crystal sample and
nano-structured compound 1 (Fig. 3a and b). The XRD patterns of
compounds 2–4 show these nano-structures have retained their
crystalline forms after grinding but as the patterns show these four
structures are completely different. The nano-structures were
characterized by Scanning Electron Microscopy (Fig. 4).
Gray nanoparticles were obtained from direct calcination of
compounds 1–4 nanostructures at 673.15 K in an electrical fur-
nace. The X-ray powder diffractions show silver metal is the ob-
tained product from calcination of compounds 1–4 (Fig. 5). The
SEM images of these silver nanoparticles were observed in Fig. 6.
The obtained silver nanoparticles have different sizes. The average
sizes of the silver nanoparticles from direct calcination of com-
pounds 1–4 have been shown in Fig. 7. The average sizes of ob-
tained silver nanoparticles from calcination of compounds 1–4
are 57, 60, 37 and 45 nm, respectively. The least size of silver nano-
particles are observed from calcination of [Ag(l-bpfb)(SCN)]n (3)
nanostructures and the maximum size of silver nanoparticles were
obtained from calcination of [Ag(l-bpfb)(ClO4)]n (2).
4. Conclusion
In summary a new 1D coordination polymer [Ag(l-bpfb)(NO3)]n
(1), as single crystal, bulk form and nano-size could convert to the
new compounds by anion exchange in solid state. By grinding the
compound 1 nanostructure and NaClO4, KSCN and NaN3 in solid
phase, the products with formulas [Ag(l-bpfb)(ClO4)]n (2), [Ag
(l
-bpfb)(SCN)]n (3) and [Ag( -bpfb)(N3)]n (4) were obtained. The
l
silver nanoparticles are prepared from calcination of compounds
1–4 at 673 K. The silver nanoparticles produced by calcination of
compound 1–4 have different sizes because of having different
structure formulas. So, the role of the counter ion in the initial
structure as precursor is very important and it has direct influence
on the size and morphology of products.
Acknowledgment
Support of this investigation by Tarbiat Modares University is
gratefully acknowledged.
Appendix A. Supplementary material
Complete bond lengths and angles, co-ordinates and displace-
ment parameters have been deposited at Cambridge Crystallogra-
phy Data Center. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.ica.2011.12.032.
Fig. 6. The SEM images of silver nanoparticles produced from calcinations of (a)
[Ag(l
-bpfb)(NO3)]n (1); (b) [Ag(
-bpfb)(N3)]n (4).
l-bpfb)(ClO4)]n (2); (c) [Ag(l-bpfb)(SCN)]n (3); and
(d) [Ag(
l

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Z.R. Ranjbar, A. Morsali / Inorganica Chimica Acta 382 (2012) 171–176
Fig. 7. The histogram of silver nanoparticles prepared by direct calcination at 673 K from compound (a) [Ag(l-bpfb)(NO3)]n (1); (b) [Ag(l-bpfb)(ClO4)]n (2); (c) [Ag(l-
bpfb)(SCN)]n (3); and (d) [Ag( -bpfb)(N3)]n (4).
l
[4] V.A. Friese, D.G. Kurth, Curr. Opin. Colloid Interface Sci. 14 (2009) 81.
[5] A.N. Khlobystov, A.J. Blake, N.R. Champness, D.A. Lemenovskii, A.G. Majouga,
N.V. Zyk, M. Schröder, Coord. Chem. Rev. 222 (2001) 155.
[6] A. Morsali, M.Y. Masoomi, Coord. Chem. Rev. 253 (2009) 1882.
[7] K. Akhbari, A. Morsali, Coord. Chem. Rev. 254 (2010) 1977.
[8] O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Nature
423 (2003) 705.
[9] S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem., Int. Ed. 43 (2004) 2334.
[10] J.L.C. Rowsell, O.M. Yaghi, Microporous Mesoporous Mater. 73 (2004) 3.
[11] L. Pan, K.M. Adams, H.E. Hermandez, X. Wang, C. Zheng, Y. Hattori, K. Kaneko, J.
Am. Chem. Soc. 125 (2003) 3062.
[12] D.F. Sun, S.Q. Ma, Y.X. Ke, T.M. Petersen, H.C. Zhou, Chem. Commun. (2005)
2663.
[13] X.C. Huang, Y.Y. Lin, J.P. Zhang, X.M. Chen, Angew. Chem., Int. Ed. 45 (2006)
1557.
[14] M.H. Zeng, X.L. Feng, W.X. Zhang, X.M. Chen, Dalton Trans. (2006) 5294.
[15] H.J. Choi, M.P. Suh, J. Am. Chem. Soc. 126 (2004) 15844.
[16] B.H. Hamilton, T.A. Wagler, M.P. Espe, Ch.J. Ziegler, Inorg. Chem. 44 (2005)
4891.
[17] K.S. Min, M.P. Suh, J. Am. Chem. Soc. 122 (2000) 6834.
[18] O.S. Jung, Y.J. Kim, Y.A. Lee, H.K. Chae, H.G. Jang, J. Hong, Inorg. Chem. 40 (2001)
2105.
[19] J.X. Ma, X.F. Huang, Y. Song, X.q. Song, W.Sh. Liu, Inorg. Chem. 48 (2009) 6326.
[20] M. Khanpour, A. Morsali, Eur. J. Inorg. Chem. (2010) 1567.
[21] B.H. Hamilton, K.A. Kelly, T.A. Wagler, M.P. Espe, Ch.J. Ziegler, Inorg. Chem. 43
(2004) 50.
Fig. 8. Thermal behavior of compound 1 (red diagrams belong to nano-size and
black ones belong to bulk-size). (For interpretation of the references in color in this
figure legend, the reader is referred to the web version of this article.)
[22] G.A. Farnum, R.L. LaDuca, Cryst. Growth Des. 10 (2010) 1897.
[23] Y.J. Zhang, T. Liu, Sh. Kanegawa, O. Sato, J. Am. Chem. Soc. 132 (2010) 912.
[24] Y.J. Zhang, T. Liu, S. Kanegawa, O. Sato, J. Am. Chem. Soc. 131 (2009) 7942.
[25] L.R. Macgillivray, G.S. Papaefstathiou, T. Friscic, T.D. Hamilton, D.K. Bu˘kar, Q.
Chu, D.B. Varshney, D.G. Georgiev, Acc. Chem. Res. 41 (2008) 280.
[26] M.J. Vela, B.B. Snider, B.M. Foxman, Chem. Mater. 10 (1998) 3167.
[27] P. Yin, R. Qu, G. Zhao, Q. Xu, Y. Tian, Ch. Bao, J. Appl. Polymer. 109 (2008) 4054.
References
[1] K. Biradha, A. Ramanan, J.J. Vittal, Cryst. Growth Des. 9 (2009) 2969.
[2] C.B. Aakeroy, N.R. Champness, C. Janiak, CrystEngComm 12 (2010) 22.
[3] L. Rajput, K. Biradha, CrystEngComm 11 (2009) 1220.