Inorganic Chemistry Communications 44 (2014) 1–5

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Inorganic Chemistry Communications

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Sonochemical syntheses of one-dimensional silver(I) supramolecularpolymer: A precursor for preparation of silver nanostructure

Shiva Hojaghani a, Kamran Akhbari b, Moayed Hossaini Sadr a, Ali Morsali c,⁎a Department of Chemistry, College of Basic Sciences, Tehran Science and Research Branch, Islamic Azad University, Tehran, Iranb School of Chemistry, College of Science, University of Tehran, P.O. Box 14155-6455, Tehran, Islamic Republic of Iranc Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14115-4838, Tehran, Islamic Republic of Iran

⁎ Corresponding author. Tel./fax: +98 21 82884416.E-mail address: Morsali_a@modares.ac.ir (A. Morsali).

http://dx.doi.org/10.1016/j.inoche.2014.02.0301387-7003/© 2014 Published by Elsevier B.V.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 4 January 2014Accepted 20 February 2014Available online 1 March 2014

Keywords:Supramolecular polymerNano-structureNanosilverSonochemicalSurfactantOleic acid

Nano-structures of one-dimensional supramolecular polymer, [Ag(Me-8-HqH)(Me-8-Hq)]n (1) [Me-8-HqH =2-methyl-8-hydroxyquinoline], have been synthesized by the reaction of Me-8-HqH and AgNO3 bysonochemical process. The single-crystal X-ray data of compound 1 shows that both two AgI ions are chelatedby two Me-8-HqH and Me-8-Hq− molecules. Coordination number of AgI ions in compound 1 is four and theyhave AgO2N2 coordination sphere. The AgI complexes in 1 are linked to each other via hydrogen bonding andform a supramolecular chain structure. Thermal decomposition of compound 1 nanostructure in oleic acid re-sults in formation of silver nano-structure. These nano-structures were characterized by X-ray powder diffrac-tion (XRD) and scanning electron microscopy (SEM). The thermal stability of compound 1 was studied bythermogravimetric (TG) and differential thermal analyses (DTA).

© 2014 Published by Elsevier B.V.

Considerable attentions have been paid to the supramolecular poly-mers composed of 1D chains, 2D sheets and 3D networks due to thepotential applications in separation, catalysis and as conductors, sensorsand storage devices [1,2]. Much interest has been focused on thesupramolecular polymeric structures constructed by coordinationbonds, hydrogen bonding and aromatic π-stacking interactions [3–6].Several different synthetic approaches have been offered for thepreparation of coordination compounds [7]. Some of them are (1)slow diffusion of the reactants into a polymeric matrix, (2) diffusionfrom the gas phase, (3) evaporation of the solvent at ambient or reducedtemperatures, (4) precipitation or recrystallisation from a mixture ofsolvents, (5) temperature controlled cooling and (6) hydrothermalsynthesis. Nanometer-sized structures of supramolecular polymers arefascinating to explore, since their unique properties are controlled bythe large number of surface molecules, which experience an entirelydifferent environment than those in a bulk crystal. Controlling thegrowth ofmaterials at the submicrometer scale is of central importancein the emerging field of nanotechnology [8–11]. Although considerableeffort has been performed to the controlled synthesis of nano-scalestructures of metals, oxides, sulfides and ceramic materials, littleattentionwas focused to date on nano-structures of supramolecular com-pounds. In this paper we describe a simple synthetic sonochemical prep-aration of AgI supramolecular polymer nano-structures. Sonochemistry is

the research area in which molecules undergo a reaction due to theapplication of powerful ultrasound radiation (20 kHz–10 MHz) [12].Ultrasound induces chemical or physical changes during cavitations, aphenomenon involving the formation, growth and instantaneouslyimplosive collapse of bubbles in a liquid, which can generate local hotspots having temperatures of roughly 5000 °C, pressures of about500 atm and a lifetime of a few microseconds [13]. These extremeconditions can drive chemical reactions, but they can also promote theformation of nano-sized structures, mostly by the instantaneous forma-tion of a plethora of crystallization nuclei [13,14]. This has been widelyused to fabricate nano-sized structures of a variety of compounds and inrecent years many kinds of nano-sized materials have been prepared bythismethod [15–24]. This article focuses on the simple synthetic prepara-tion of AgI supramolecular polymer nano-structures by sonochemicalprocess. In addition, nano-structures of [Ag(Me-8-HqH)(Me-8-Hq)]n (1)[Me-8-HqH = 2-methyl-8-hydroxyquinoline] supramolecular polymer,have been used as new precursors for preparation of silver nano-structures by thermal decomposition in oleic acid.

The Scheme 1 shows the reaction between silver(I) nitrate and2-methyl-8-hydroxyquinoline by two different methods.

Single crystal X-ray diffraction analyses (Tables S1 and S2) ofcompound 1 show that two types of AgI ions exist in this complex.Each of them is chelated by two Me-8-HqH and Me-8-Hq− molecules(Fig. 1). Fig. 1 shows the ORTEP view of both independent molecules.Thermal displacement ellipsoids are shown at 50% probability level ineach independent molecule, the H atom of OH group is disordered

Evaporation in MeCN solvent

By sonochemical process

Calcination at 673 K

In OA at 453 K

Silver micro-structure

Silver nano-structure

Nano-structure of compound 1AgNO3+[(Me-8-HqH)(Me-8-Hq)]

Single crystal of compound 1

Scheme 1. The produced materials from the reaction of [(Me-8-HqH)(Me-8-Hq−)], [Me-8-HqH = 2-methyl-8-hydroxyquinoline] with silver(I) nitrate by two different methods andfabrication of silver micro- and nano-structures from compound 1 nano-supramolecular polymer.

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over two positions with equal occupancies. So, in each independentmolecule, only one OH group presents. The second ligand is Me-8-Hq−

anion. Indeed, 2-methyl-8-hydroxyquinoline acts as bidentatechelating ligand with two forms of protonated (Me-8-HqH) anddeprotonated (Me-8-Hq−) ligands. The AgI ions in 1 are coordinatedby two N and two O atoms of Me-8-HqH and Me-8-Hq− ligand(Fig. 1). The AgI complexes in 1 were linked to each other viahydrogen bonding to form a supramolecular chain structure alongthe crystallographic b axis (Table S3 and Fig. 2). Our search showsthat the AgI ions in compound 1 unlike two polymorphs of [Ag(8-HqH)(8-Hq)]n (α and β), (8-HqH: 8-hydroxyquinoline and 8-Hq−:8-hydroxyquinolate) [25] do not involve in polyhapto Ag⋯C interac-tions with the phenyl group of neighboring [Ag(Me-8-HqH)(Me-8-Hq)] units. Thus the complex could be considered to contain twotypes of AgI ions with AgO2N2 coordination sphere. No π–π stackinginteraction exists in 1, too.

Fig. 3b shows the XRD pattern of a typical sample of [Ag(Me-8-HqH)(Me-8-Hq)]n (1) prepared by the sonochemical process from0.1(Me-8-HqH):0.05(Ag+) M solutions of initial reagents underultrasonic waves. An acceptable match, with slight differences in 2θ,was observed between the simulated pattern from single-crystal X-raydata (Fig. 3a) and the pattern from experimental data (Fig. 3b). Resultsof XRD powder patterns indicate that the experimental data are in good

Molecule 1

Fig. 1. ORTEP view of both independent molecules. Thermal displacement ellipsoids are shodisordered over two positions with equal occupancies. So, in each independent molecule, only

agreement with the simulated XRD powder pattern based on singlecrystal X-ray data, hence this compound obtained as a mono-phase.The morphology, structure and size of the two samples which wereprepared by sonochemical process are investigated by a ScanningElectron Microscopy (SEM). Fig. 4 (up and down) shows the SEMimages of compound 1 nano-structures prepared by sonochemicalprocess in ultrasonic bath from the reaction of 0.05:0.1 and 0.1:0.2 Mconcentrations of initial reagents, respectively. As could be observedfrom this figure, acceptable results were obtained from this process tofabricate compound 1 nano-structure. But as it is obvious, concentrationincrease from 0.05:0.1 to 0.1:0.2 M of initial reagents results in agglom-eration of nano-structures, thus preparation of compound 1 nano-structure from 0.05:0.1 M concentration of initial reagents is moreappropriate than the 0.1:0.2 M concentration of initial reagents.

Thermogravimetric (TG) and differential thermal analyses (DTA) ofcompound 1 nano-structure show that this compound is stable up to98 °C (Figure S1), at which temperature decomposition of compound1 nano-structure starts in two steps with two endothermic effects at130 and 250 °C, respectively. In these two steps, removal of protonated(Me-8-HqH) and deprotonated (Me-8-Hq−) ligands occurs between 98°C and 700 °C with a mass loss of 80.5% (calcd 74.82%). Mass loss calcu-lations and XRD pattern (Fig. 3c) show that the final decompositionproduct is metallic silver. It should be mentioned that C. Janiak et al.

Molecule 2

wn at 50% probability level in each independent molecule, The H atom of OH group isone OH group presents that the second ligand is anion.

Fig. 2. Showing the formation of one-dimensional supramolecular structure via hydrogen bonding interaction in compound 1.

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also showed that supramolecular Ag compounds can given rise toelemental silver by temperature induced [26] or light-induced [27]processes.

Fig. 3c attributed to the XRD pattern of the residue obtained fromcalcination of compound 1 nanostructure at 673K. The obtained patternmatches with the standard patterns of cubic silver with the latticeparameters (a = 4.0862 Å and z = 4) which are close to the reportedvalues, (JCPDS card number 04–0783). SEM image (Fig. 5, up) of theresidue obtained from the calcination of compound 1 nano-structureat 673 K shows that micro-structure of metallic silver were agglomerat-ed to form this spongy solid. This spongy metallic silver structure hasagglomerated from 0.15 to 1.0 μm size of micro-particles (with theaverage diameter of about 0.55 μm). Formation of this spongy solid is

Fig. 3. XRD patterns; a) simulated pattern based on single crystal data of compound 1, b)nano-structure of compound 1 prepared by sonochemical process from 0.1(Me-8-HqH):0.05(Ag+) M solutions of initial reagents, c) silver micro-structure prepared bythe calcination of compound 1 nanostructure and d) silver nano-structure prepared bythermal decomposition of compound 1 nanostructure in oleic acid at 453 K.

due to decomposition of Me-8-HqH ligand which accompanied withremoval of resulting gas such as CO2. In order to obtain silver nano-structure from nano-structure of compound 1 and to prevent fromagglomeration, oleic acid was used as a surfactant until the thermaldecomposition of compound 1 occurs in the resulting micelles [28].XRD pattern of residue (Fig. 3d), shows that the resulting residue wascubic silver with the lattice parameters mentioned above. SEM imagesof the resulting residue show the formation of silver nano-structureagglomerated from nano-particles having diameters between 40 and

Fig. 4. SEM images of compound 1 nano-structures prepared by sonochemical processfrom 0.1:0.05 M (up) and 0.2:0.1 M (down) concentrations of initial reagents.

Fig. 5. SEM images of spongy silver micro-structure prepared by the calcination ofcompound 1 nano-structure at 673 K (up) and silver nano-structure prepared by OA at453 K (down).

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100 nm (with the average diameter of about 54 nm), (Fig. 5 down).Thus compound 1 nano-structures are good precursors for preparationof silver nano-structure by thermal decomposition in oleic acid.

Conclusions

The nano-structures of [Ag(Me-8-HqH)(Me-8-Hq)]n (1) supramo-lecular polymer with one-dimensional chain structure, as a result ofhydrogen bonding interaction, were synthesized by sonochemicalprocess. Concentration increase of initial reagents results in agglomera-tion of compound 1 nano-structure. Coordination number of AgI ions incompound 1 is four and they have AgO2N2 coordination sphere.Compound 1 is a new precursor for preparation of metallic silver. Thecalcination of compound 1 nano-structure, which obtained fromsonochemical process, leads to formation of agglomerated silvermicro-structure. Thus calcination is not an appropriate process for thepreparation of silver nano-structure from compound 1. We successfullyprepared silver nano-structure with the average diameter of 54 nmfrom the thermal decomposition of compound 1 nano-structure inoleic acid at 453 K. Indeed, thermal treatment of sonochemicallysynthesized nano-structure of compound 1with oleic acid led to forma-tion of nano-structure of metallic silver. This paper is one of the fewsamples using sonication as an alternative synthetic procedure to formsupramolecular polymers. Thismethod for preparation of supramolecu-lar polymers may be had some advantages such as: it takes places inshorter reaction times, produces better yields and also it may producethe polymers at nano-size. From this perspective, further systematic

studies of other polymers with different metal ions are ongoing in ourlaboratory, which may offer new insights into metal–organic supramo-lecular assembly and nano-chemistry.

Acknowledgments

The support of this investigation by Islamic Azad University,University of Tehran, and Tarbiat Modares University is gratefullyacknowledged.

Appendix A. Supplementary material

Complete bond lengths and angles, co-ordinates and displacementparameters have been deposited at Cambridge Crystallography DataCenter. Supplementary data are available from the CCDC, 12 UnionRoad, Cambridge CB2 1EZ, UK on request, quoting the depositionnumber 935401 for compound 1. Supplementary data associated withthis article can be found, in the online version, at http://dx.doi.org/10.1016/j.inoche.2014.02.030.

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