Inorganica Chimica Acta 398 (2013) 151–157
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Sonochemical syntheses of nano lead(II) iodide triazole carboxylate coordination
polymer: Precursor for facile fabrication of lead(II) oxide/iodide nano-structures
Vahid Safarifard, Ali Morsali ⇑
Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14115-4838, Tehran, Islamic Republic of Iran
a r t i c l e
i n f o
Article history:
Received 7 September 2012
Received in revised form 10 December 2012
Accepted 13 December 2012
Available online 27 December 2012
Keywords:
Coordination polymer
Nano-structure
Sonochemical
Thermal decomposition
Lead(II) oxide
Lead(II) iodide
a b s t r a c t
Nanoparticles of a one-dimensional coordination polymer [Pb(L)(l2-I)]n (1), (L = 1H-1,2,4-triazole3-carboxylate), have been synthesized by a sonochemical process and characterized by field emission
scanning electron microscopy (FESEM), X-ray powder diffraction (XRPD), FT-IR spectroscopy and elemental analyses. The thermal stability of compound 1 both its bulk and nano-size has been studied by thermal
gravimetric (TG) and compared each other. Concentration of initial reagents effects and the role of power
ultrasound irradiation on size and morphology of nano-structured compound 1 have been studied and
show that low concentrations of initial reagents and also high power of ultrasound irradiation decreased
particles size and leaded to uniform nanoparticles morphology. PbO nano-structures were simply synthesized by solid-state transformation of compound 1 at 630 °C under air atmosphere whereas thermal
decomposition of compound 1 in oleic acid as surfactant at 200 °C yield PbI2 nanoparticles.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
During the last two decades, the rational design and syntheses
of novel metal coordination polymers with multi-dimensional
networks, which involves self-assembly of organic multitopic ligands with appropriate functional groups and metallic centres,
with potentially useful applications as functional materials, ion exchange, catalysis, luminescence, magnetism, nonlinear optics, and
molecular sensing, have made considerable progress in the field
of coordination chemistry and crystal engineering [1–8]. The size
and shape of solid materials influence on the chemical and physical
properties. By decreasing the size of coordination polymers as in
nano-size, surface area would be increased. Hence making coordination polymers in any form in nano-scale is certainly a major step
forward toward the technological applications of these new
materials [9,10].
The synthesis of lead(II) coordination polymers is an increasingly active area due to presence of a 6s2 electron configuration
and stereoactivity of the valence shell lone electron pair and
according to directed ligands classify as holodirected and hemidirected [11]. In this paper we would like to describe a simple synthetic sonochemical preparation of nano-structured lead(II) 1D
coordination polymer, [Pb(L)(l2-I)]n (1), (L = 1H-1,2,4-triazole-3carboxylate). The 1H-1,2,4-triazole-3-carboxylic acid (HL) contains
⇑ Corresponding author. Tel.: +98 21 82884416; fax: +98 21 8009730.
E-mail address: [email protected] (A. Morsali).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.12.029
1,2,4-triazole and one carboxylic acid functional group and to date
some interesting coordination polymers with this ligand have been
reported [12–15]. Sonochemistry is the research area in which
molecules undergo a reaction due to the application of powerful
ultrasound radiation (20 kHz–10 MHz) [16]. Ultrasound induces
physical or chemical changes during cavitation (the formation,
growth, and instantaneously implosive collapse of bubbles in a liquid) which can generate local hot spots having temperatures of
roughly 5000 K, pressures of about 500 atm and a lifetime of a
few microseconds; These extreme conditions not only can propel
chemical reactions, but also promote the formation of nano-sized
structures, mostly by the instantaneous formation of a plethora
of crystallization nuclei [17–20].
Lead oxides are very fascinating because several compounds exist, with a variety of oxidation states and mixed-valence species.
Till now, many methods have been developed to synthesize PbO
nanocrystals including vapor phase growth [21], vapor–liquid–solid process [22], electrophoretic deposition [23], sol–gel process
[24], homogeneous precipitation [25], etc. The use of metal coordination polymers as precursors for the preparation of inorganic
nanomaterials such as lead(II) oxide has not yet been investigated
thoroughly [26]. To proceed, we report the facil synthesis of lead(II)
oxide nano-structures by solid-state transformation of compound
1 calcined at 630 °C in air and without any surfactant or capping
molecules as well as synthesis of lead(II) iodide nanoparticles by
thermal decomposition of compound 1 in oleic acid as a surfactant
at 200 °C.
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2. Experimental
2.1. Materials and physical techniques
Starting reagents for the synthesis were purchased and used
without further purification from commercial suppliers (Sigma–
Aldrich, Merck and others). Melting points were measured on an
Electrothermal 9100 apparatus. Elemental analyses (carbon,
hydrogen, and nitrogen) were performed using a Heraeus CHNO- Rapid analyzer. The infrared spectra were recorded on a Nicolet
Fourier Transform IR, Nicolet 100 spectrometer in the range
500–4000 cm 1 using the KBr disk technique. Thermogravimetric
analysis (TGA) of the title compound were performed on a computer-controlled PL-STA 1500 apparatus. Single-phased powder
sample of 1 was loaded into alumina pans and heated with a ramp
rate of 10 °C/min from room temperature to 600 °C under argon
atmosphere. X-ray powder diffraction (XRPD) measurements were
performed using a Philips X’pert diffractometer with monochromated
Co Ka radiation (k = 1.78897 Å). The simulated XRD powder pattern
based on single crystal data were prepared using Mercury software
[27]. Ultrasonic generators were carried out on a SONICA-2200 EP,
40 kHz/305 W and TECNO-GAZ, S.p.A., Tecna 6, 35 kHz/138 W. The
samples were characterized by a field emission scanning electron
microscope (FESEM) (Hitachi S-4160) with gold coating.
2.2. Synthesis of [Pb(L)(l2-I)]n (1)
Compound 1 was prepared using the branched tube method
[11]: 1H-1,2,4-triazole-3-carboxylic acid (0.117 g, 1 mmol), potassium iodide (0.166 g, 1 mmol) and lead(II) nitrate (0.331 g,
1 mmol) were placed in the arm to be heated. Water was carefully
added to fill both arms, and then the arm to be heated was placed
in a bath at 60 °C. After 10 days, yellow crystals were deposited in
the cooler arm which were filtered off, washed with water and air
dried. (0.28 g, yield 63%), m.p. > 300 °C. Anal. Calc. for C3H2IN3O2Pb: C, 8.07; H, 0.45; N, 9.41. Found: C, 8.15; H, 0.43; N, 9.63%. IR
(cm 1) selected bands: 810(m), 981(m), 1280(m), 1453(vs),
1622(vs), 3102(br) and 3444(br).
Scheme 1. Materials produced and synthetic methods.
Fig. 1. IR spectra of (a) nanoparticles of compound 1 produced by sonochemical method, (b) bulk materials as synthesized of 1.
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153
Fig. 2. XRD patterns; (a) simulated pattern based on single crystal data of compound 1, (b) as synthesized and (c) nanostructure of compound 1 prepared by sonochemical
process.
2.3. Synthesis of [Pb(L)(l2-I)]n (1) nanostructure by a sonochemical
process
To prepare nano-sized [Pb(L)(l2-I)]n (1), 50 ml solution of lead(II) nitrate (0.1 M) in water was positioned in a high-density
ultrasonic probe, operating at 35 kHz with a maximum power output of 138 W. Into this solution water a 50 ml solution of the ligand
1H-1,2,4-triazole-3-carboxylic acid (0.1 M) and sodium hydroxide
(0.1 M) and potassium iodide (0.1 M) were added dropwise. The
obtained precipitates were filtered off, washed with water and
then dried in air. m.p. > 300 °C. Found: C, 8.32; H, 0.51; N, 9.22%.
IR bands: 819(m), 995(m), 1286(m), 1457(vs), 1626(vs), 3113(br)
and 3422(br).
For study of the effect of concentration the initial reagents and
the role of power ultrasound irradiation on size and morphology of
nano-structured compound 1, the above processes were done with
concentrations of 0.05 and 0.01 M and electrical powers of 138 and
305 W from the ultrasonic generators.
2.4. Synthesis of PbO nanostructures by thermal decomposition of
compound 1
Nanoparticles of compound 1 (446 mg, 1 mmol) transferred to a
crucible (10 mL capacity). The crucible was transferred to furnace
and heated at 630 °C under static atmosphere of air for 4 h. The
furnace was cooled to 35 °C. The organic components were
combusted and PbO nanostructures were produced. The XRD pattern shows the product is PbO.
2.5. Synthesis of PbI2 nanoparticles by thermal decomposition of
compound 1 in oleic acid as a surfactant
The 0.446 g of the yellow single crystals of compound 1 were
dispersed in oleic acid, (8 mL, 25 mmol) to form a homogenous
emulsion solution. This solution was stirring for 15 min at mild
heating (60 °C) and then heated to 200 °C in an electric furnace under air atmosphere for 2 h. Two milliliter of toluene and a large excess of EtOH (20 ml) were added to the reaction solution.
Nanoparticles of lead(II) iodide was separated after washing with
ethanol. The solid was washed with EtOH and dried.
3. Results and discussion
Reaction of 1H-1,2,4-triazole-3-carboxylate (L ) and potassium
iodide with lead(II) nitrate leads to formation of a 1D coordination
polymer [Pb(L)(l2-I)]n (1). Nano-structure of compound 1 were obtained in aqueous solution by ultrasonic irradiation, while single
Fig. 3. FESEM photograph of compound 1 nanoparticles prepared by ultrasonic
generator 138 W in concentration of initial reagents [Pb2+] = [L ] = [I ] = 0.1 M in
two different scale bars.
crystals of compound 1 were prepared by a heat gradient applied
to a aqueous solution of the reagents (the ‘‘branched tube method’’) [11]. Scheme 1 gives an overview of the methods used for
the synthesis of [Pb(L)(l2-I)]n using the two different routes.
The elemental analysis and IR spectra of the nano-structure produced by the sonochemical method and of the bulk material produced by the branched tube method are indistinguishable (Fig. 1).
The triazole out of plane rings absorption can be observed
655 cm 1. The symmetric and asymmetric vibrations of the carboxylate group are observed as two strong bands at 1453 and
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Fig. 4. FESEM photograph of compound 1 nanoparticles prepared by ultrasonic
generator 138 W in concentration of initial reagents [Pb2+] = [L ] = [I ] = 0.05 M in
two different scale bars.
Fig. 5. FESEM photographs of compound 1 nanoparticles prepared by ultrasonic
generator 305 W in concentration of initial reagents [Pb2+] = [L ] = [I ] = 0.01 M in
two different scale bars.
1622 cm 1, respectively. The D(mas – msym) values indicate that the
carboxylate anions coordinate to the Pb(II) center in bridging mode.
Fig. 2 shows the simulated XRD pattern from single crystal
X-ray data of compound 1 (Fig. 2a) in comparison with the XRD
pattern of the single crystals compound 1 as synthesized
(Fig. 2b) and a typical sample of compound 1 prepared by the
sonochemical process (Fig. 2c). Acceptable matches, with slight
differences in 2h, were observed between the simulated and experimental powder X-ray diffraction patterns. This indicates that the
compound obtained by the sonochemical process as nano-structures is identical to that obtained by single crystal diffraction.
The significant broadening of the peaks indicates that the particles
are of nanometer dimensions.
The reaction between 1H-1,2,4-triazole-3-carboxylate (L ) and
potassium iodide with lead(II) nitrate provided a crystalline material of the general formula [Pb(L)(l2-I)]n (1). The morphology and
size of compound 1 prepared by the sonochemical method was
characterized by field emission scanning electron microscopy (FESEM). Fig. 3 shows the field emission scanning electron microscopy
(FESEM) of the compound 1 prepared by ultrasonic generator
138 W in concentration of initial reagents [Pb2+] = [L ] = [I ] = 0.1 M.
Another high-density ultrasonic probe, operating at 40 kHz with a
maximum power output of 305 W and different concentrations of
lead(II) nitrate and ligands 1H-1,2,4-triazole-3-carboxylate (L )
and potassium iodide solution (0.05 and 0.01 M) were tested
(Figs. 4 and 5).
Appropriate nano-sized particles of compound 1 were obtained
at a concentration of 0.01 M and with electrical power of 305 W
from the ultrasonic generator (Fig. 5). Morphology and particle
sizes of the nanostructures depend on the concentration of initial
reagents and also power of ultrasound irradiation. In order to
investigate the role of concentration of initial reagents and power
ultrasound irradiation on the nature of products, reactions were
performed under two different powers of ultrasound irradiation
with three different concentrations of initial reagents. Comparison
between the samples with different concentrations and different
electrical powers from the ultrasonic generators shows that reduction of concentrations of initial reagents and simultaneously
increasing the electrical power of ultrasonic generator decrease
the particles size and also lead to uniform nanoparticles morphology. Thus, particles sizes produced using lower concentrations of
initial reagents and higher ultrasound irradiation (0.01 M with
305 W, Fig. 5) are smaller than particles size produced using higher
concentrations and lower irradiation (0.1 and 0.05 M with 138 W,
Figs. 3 and 4, respectively). Figs. 3 and 4 illustrate agglomerated
nanoparticles obtained under 0.1 and 0.05 M concentrations of initial reagents, respectively. The IR spectrum and XRD pattern of typical samples of compound 1 prepared by the sonochemical process
at concentrations of 0.1, 0.05 and 0.01 M and different powers of
ultrasound irradiation are also same with the crystalline sample.
These experiments indicate that the reaction at three different concentrations and under two different electrical powers of ultrasonic
generator produces the same product but that the morphologies
and sizes of the particles are different.
In 1, the PbII ion is in the hemidirected geometry and fivecoordinated with one nitrogen atom, two oxygen atoms from the
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155
Fig. 6. A fragment of the 3D framework in compound 1, viewed along b direction.
Fig. 8. XRD pattern of PbO nanostructure prepared by calcination of compound 1 at
630 °C.
Fig. 7. Thermal behavior of compound 1 as bulk and nanoparticle.
L anions and two iodide ions. One l1,1-I ligand and the L anions
act as bridging ligands to join neighboring lead(II) centers to form a
1D linear chain. The subtle combination of Pb I interactions and
hydrogen bonding serves to connect these 1D coordination chains
to 2D layered networks, and then a 3D framework. A view of the
coordination environment around the lead(II) ion and packing of
compound 1 is shown in Fig. 6. The title complex crystallizes in
the orthorhombic space group Pbca.
To examine the thermal stability of the nanoparticles and the
single crystals of compound [Pb(L)(l2-I)]n (1), thermal gravimetric
analyses (TGA) were carried out between 25 and 600 °C under
argon flow (Fig. 7). The compound 1 is stable up to 210 °C and
decomposition takes places between 210–652 °C with a mass loss
54.5%. The solid residue formed at around 652 °C is suggested to
be PbO (observed: 45.5, calcd: 50.1%). Nano-sized compound 1 is
less stable and starts to decompose at 187 °C. Detectable decomposition of the nanoparticles of 1 thus starts about 23 degree earlier
than that of its bulk counterparts, probably due to the much higher
surface to volume ratio of the nanoparticles, as more heat is
needed to annihilate the lattices of the bulk materials.
Ligand-free PbO nano-structure was simply synthesized by
solid-state transformation of compound 1 at 630 °C under air
atmosphere for 4 h. Fig. 8 provides the XRD pattern of the residue
obtained from the calcination of compound 1. The obtained pattern
matches with the standard pattern of PbO with the lattice parameters (a = 3.9729 Å, c = 5.0217 Å, S.G. = P4/nmm and z = 2) which is
the same as the reported values (JCPDS card number 05–0561). As
Fig. 9. FESEM image of agglomerated PbO nanoparticles prepared by calcination of
compound 1 nanoparticles at 630 °C.
the calcination process was successful for the preparation of PbO,
we used the nano-sized compound 1 prepared by the sonochemical process at a concentration of 0.1 M and 138 W power of ultrasonic irradiation for the preparation of PbO nanoparticles. The XRD
pattern of the residue shows that the resulting residue was again a
PbO with the lattice parameters mentioned above. The SEM image
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Fig. 10. XRD pattern of PbI2 nanoparticles prepared by treatment with oleic acid as a surfactant at 200 °C.
which are in JCPDS card file No. 73–1750. No characteristic peaks
of impurities are detected in the XRD pattern. Fig. 11 shows the
SEM image of the PbI2 nanoparticles obtained from calcination of
compound 1 in oleic acid as a surfactant at 200 °C for 2 h.
4. Conclusions
A nano-sized Pb(II) coordination polymer, {[Pb(L)(l2-I)]n (1),
L = 1H-1,2,4-triazole-3-carboxylate} was synthesized by sonochemical irradiation and compared with its crystalline structure.
Compound 1 was characterized by X-ray powder diffraction
(XRD), IR spectroscopy and thermal gravimetric (TG). To prepare
the nanostructure of compound 1, three different concentrations
of initial reagents, 0.1, 0.05 and 0.01 M, and different power ultrasound irradiation, 138 and 305 W, were tested. Appropriate nanosized compound 1 were obtained at concentration of 0.01 M and
power ultrasound irradiation 305 W. Morphology and particle
sizes of the nanostructures depend on the concentrations of initial
reagents and power ultrasound irradiation. Results show a decrease in the particles size and also uniformed nanoparticles morphology as the concentration of initial reagents is decreased and
simultaneously the electrical power of ultrasonic generator is increased. Calcination of the nano-sized compound 1 at 630 °C in a
furnace and static atmosphere of air for 4 h yields agglomerated
PbO nanoparticles whereas PbI2 nanoparticles were prepared by
thermal decomposition of compound 1 in oleic acid as a surfactant
at 200 °C.
Acknowledgement
Support of this investigation by Tarbiat Modares University is
gratefully acknowledged.
Fig. 11. FESEM image of PbI2 nanoparticles prepared by treatment with oleic acid as
a surfactant at 200 °C.
of the resulting residue shows the formation of agglomerated PbO
nanoparticles (Fig. 9).
Nanoparticles PbI2 have been generated by thermal decomposition of compound 1 in oleic acid as surfactant at 200 °C under air
atmosphere for 2 h. The final product upon calcination of compound 1 is, based on their XRD pattern, hexagonal PbI2 (Fig. 10).
This is the first time during our research in our laboratory that
we synthesized hexagonal PbI2 by calcination of our coordination
polymers [28]. The phase purity of the as-prepared hexagonal
PbI2 nanoparticles are completely obvious and all diffraction peaks
are perfectly indexed to the hexagonal PbI2 structure with the lattice parameters of a = 4.557 Å, c = 6.979 Å, Z = 1 and S.G = P-3 m1
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