ARTICLE

DOI: 10.1002/zaac.201100492

Direct Synthesis of PbO Nanoparticles From a Lead(II) Nano CoordinationPolymer Precursor: Synthesis, Crystal Structure, and DFT Calculations of

[Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n with the First Pb2-(μ-ClO4)2 Unit

Babak Mirtamizdoust,[a] Behrouz Shaabani,*[a] Aliakbar Khandar,[b] Hoong-Kun Fun,[c]

Shiping Huang,[d] Muhammad Shadman,[e] and Pejman Hojati-Talemi[f]

Keywords: Coordination polymers; Lead; Azides; Nanostructures; X-ray crystallography

Abstract. Nanostructures of a new coordination polymer of divalentlead with the ligand 2,9-dimethyl-1,10-phenanthroline (dmp) contain-ing the first Pb2-(μ-ClO4)2 motif, [Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n (1),was synthesized by a sonochemical method that produces the coordina-tion polymers at nano size. The new nanostructure was characterizedby scanning electron microscopy, X-ray powder diffraction, IR, 1HNMR and 13C NMR spectroscopy, and elemental analysis. Compound1 was structurally characterized by single-crystal X-ray diffraction andthe single-crystal X-ray data shows that the coordination number ofPbII ions is six, (PbN4O2), with two N-donor atoms from aza-aromaticbase ligands and four O-donors from two perchlorate anions and twoN-donors from two azide anions. It has a “stereo-chemically active”

Introduction

Crystal engineering, the design and synthesis of supramolec-ular metal complexes (coordination polymers) with flexibleframeworks is a frontier field in research, not only for theirvariety of architectures and interesting molecular topologiesbut also because of their potential applications as zeolite-likecatalysts, in host-guest chemistry, gas storage, ion exchange,molecular recognition, as photonic materials, and in magnetic,

* Prof. Dr. B. ShaabaniFax: +98-411-3340191E-Mail: shaabani_b@yahoo.com

[a] Synthesis of Inorganic Compounds Research LaboratoryFaculty of ChemistryUniversity of TabrizTabriz, Iran

[b] Coordination Chemistry Research LaboratoryFaculty of ChemistryUniversity of TabrizTabriz, Iran

[c] X-ray Crystallography UnitSchool of PhysicsUniversity of Sains Malaysia11800 USM, Penang, Malaysia

[d] College of Chemical EngineeringBeijing University of Chemical TechnologyBeijing, P. R. China

[e] Department of ChemistryFaculty of ScienceUniversity of ZanjanP.O.Box 45195–313, Zanjan, Iran

[f] Mawson InstituteUniversity of South AustraliaMawson Lakes SA 5095, Australia

© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2012, 638, (5), 844–850844

electron lone pair, and the coordination sphere is hemidirected. Thesupramolecular features in these complexes are guided and controlledby weak directional intermolecular interactions. The chains interactwith each other through π–π stacking interactions creating a 3D frame-work. The structure of the title complex was optimized by densityfunctional theory calculations. Calculated structural parameters and IRspectra for the title complex are in agreement with the crystal structure.The PbO nanoparticles were obtained by thermolysis of 1 at 180 °Cwith oleic acid as a surfactant. The average diameter of the nanopar-ticles was estimated by the Scherrer equation to be 23 nm. The mor-phology and size of the prepared PbO samples were further observedusing SEM.

electronic, and optical devices.[1] In this aspect, considerableprogress was made on the theoretical prediction and network-based approaches for controlling the topology and structuresof the networks to produce useful functional materials.[2] Incomparison with the s, d, or f metal coordination polymers thathas been mainly focused on up to now, less consideration hasbeen given to the heavy metals of the p block as coordinationcenters, despite their important applications in electrolumines-cent devices, fluorescence, sensors, photovoltaic convertors,and organic light-emitting diodes.[3] Lead(II) frameworks haveadditionally attracted great interest because of lead’s large ionradius, a variable coordination number, and the possible occur-rence of a stereochemically active lone pair of 6s2 outer elec-trons as well as novel network topologies.[4] According to thehard-soft acid-base theory, the intermediate coordination abil-ity of lead(II) means that it can flexibly coordinate small nitro-gen or oxygen atoms as well as large sulfur atoms.[5] The in-vestigation of “stereo-chemical activity” of valence shell elec-tron lone pairs in polymeric and supramolecular compoundsmay be more interested and the spontaneous aggregation ofseveral bridging ligands may causes the gap is disappeared andthe coordination of lead(II) takes less common holodirectedarrangement.[6]

In contrast to ordinary inorganic compounds, reports of thesynthesis of nano coordination polymers are surprisinglysparse. Until recently there have been only very few reportsinto the syntheses and properties of nanomaterials made up of

[Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n with the First Pb2-(μ-ClO4)2 Unit

coordination polymers. The use of organometallic coordinationpolymers as precursors for the preparation of inorganic nanom-aterials has not yet been investigated thoroughly. Sonochemis-try is the research area, in which chemical reactions are influ-enced by the application of powerful ultrasound radiation(20 KHz–10 MHz). Recently the application of ultrasound insynthetic organic chemistry has gathered attention becauseultrasonic waves in liquids are known to cause chemical reac-tions either in homogeneous or in heterogeneous systems.[7]

Solid energetic materials have long played an importanttechnological role as explosives. Metal azides serve as a proto-type for more complex energetic solids. Attempts at character-izing the probable solid-state electronic structure of metal az-ides are described in a review article by Young.[8] Lead azideis a sensitive primary explosive frequently used in primers,blasting caps, and fuses. The alkali metal azide systems aremuch more benign in behavior. Therefore, to gain an under-standing of the behavior patterns observed, one should knowthe importance of the fundamental electronic structure proper-ties of this class of solids.[9]

The first lead(II) coordination polymer with azido bridgingligand was synthesized in our research group and recently wehave reported the first theoretical study of lead(II)-azido com-plexes and synthesized a nano lead(II)-azido coordinationpolymer.[10] As a continuation of the previous study, in thispaper we extend these experimental and theoretical studies toinvestigate the interactions of this versatile bridging ligand (az-ide anion) and the first perchlorate anion bridging ligand withlead(II) ions in the presence of aromatic amines and describea simple synthetic sonochemical preparation of nanostructuresof this coordination polymer and its use in the preparation ofPbO nanoparticles.

Results and Discussion

Spectroscopic Studies

The reaction of the “dmp” ligand with a mixture ofPb(ClO4)2 and sodium azide using two different routes pro-vided crystalline materials of the general formula [Pb2(dmp)2-(μ-N3)2(μ-ClO4)2]n (1). Scheme 1 gives an overview of themethods used for the synthesis of [Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n

(1) using two different routes.

Scheme 1. Materials produced and synthetic methods.

The elemental analysis and IR spectra of the nanostructuresand the single crystalline material are indistinguishable. TheIR spectra of the nanostructures and the single crystalline ma-terials show the characteristic absorption bands of the “dmp”ligand. The selected spectroscopic data and the corresponding

Z. Anorg. Allg. Chem. 2012, 844–850 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 845

data obtained from DFT calculations are given in Table 1. Therelatively weak band around 3058 cm–1 is attributed to the ab-sorption of the aromatic CH hydrogen atoms and the bandaround 2994 cm–1 is attributed to the absorption of the ali-phatic CH hydrogen atoms. The band at 1130 cm–1 is due tothe ClO4

– stretching vibration. The strong doublet at 2055–2065 cm–1 corresponds to νasym(N3

–) and indicates the end-on(μ-1,1) bonding mode of N3

–.[13] The 1H NMR spectrum ofthe DMSO solution of 1 displays a distinct peak at δ =2.75 ppm, which is assigned to the aliphatic protons of the“dmp” ligand. The peaks at 7.75, 7.90, and 8.35 ppm are as-signed to the aromatic protons of the “dmp” ligand. The 13CNMR spectrum of the DMSO solution of compound 1 displayssix distinct peaks, which are assigned to the aromatic carbonsof the “dmp” ligand and another peak at δ = 28 ppm, which isassigned to the methyl group carbons of the “dmp” ligand.

Table 1. Experimental FT-IR frequencies /cm–1 for [Pb2(dmp)2-(μ-N3)2(μ-ClO4)2]n (1), compared with the theoretical frequencies ob-tained from DFT calculations.

Assignment Experimental Calculated

ν(C–H)aliphatic 2994 m 3005ν(C–H)aromatic 3058 w 3090ν(C–H) 675 m 715ν(CC) 1470 s, 1515 s 1490, 1591ν(ClO4)– 1130 vs 1180ν(N3)– 2055 vs, 2065 s 2073, 2096ν(Pb–N) 390

Figure 1 shows the XRPD pattern calculated from the singlecrystal data (see below) of compound 1 in comparison with

Figure 1. The XRPD patterns of (a) computed from single-crystal X-ray data of compound 1. (b) Nanostructure of compound 1.

B. Shaabani et al.ARTICLEthe XRPD pattern of the typical nanorod sample of 1 preparedby a sonochemical process (Figure 1a and b, respectively).

The acceptable match, with very slight differences in peakpositions, observed between the simulated and experimentalpowder X-ray diffraction patterns (Figure 1) indicates that thenanorod sample is a single crystalline phase identical to thatobtained by single crystal diffraction. The significant broaden-ing of the peaks of the nanostructure (Figure 1b) indicates thatthe particles are of nanometer dimensions. The average size ofthe particles was estimated by the Scherrer formula, D =0.891λ/βcos(θ), where D is the average grain size, λ the X-raywavelength (1.5418 Å), θ the diffraction angle, and β the full-width at half maximum of an observed peak. The obtainedvalue is D = 60 nm. Figure 2 shows the nanorod that observedby scanning electron microscopy. The morphology of com-pound 1 prepared by the sonochemical method (Figure 2) isrods with a thickness of about 60 nm. The mechanism of for-mation of this structure needs to be further investigated; how-ever it may be influenced by the crystal structure of the com-pound, which is a one-dimensional rod-like shape (see below).

The determination of the structure of [Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n by single-crystal X-ray crystallography[14] showedthat the complex crystallizes in the monoclinic system withspace group C2/c, taking the form of a one dimensional poly-mer in the solid state (Figure 3). Each lead atom is chelated

Figure 2. SEM photographs of [Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n (1)nanorods.

Figure 3. Fragment of the coordination polymer showing the 1D polymer.

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by two nitrogen atoms of “dmp” with Pb–N distances of2.558(6) and 2.528(5) Å, two azide anions with Pb–N dis-tances of 2.393(5) and 2.602(7) Å, and two perchlorate oxygenatoms with Pb–O distances of 2.880(5) and 2.873(4) Å withhemidirected arrangement[4a](Figure 3).

This arrangement suggests a gap or hole in coordination en-vironment around the metal ions occupied possibly by a “ste-reo-active” lone pair of electrons on lead(II).[4a] The observedshortening of the Pb–N bonds on the side of Pb2+ ion oppositeto the putative lone pair [2.393(5) Å compared with 2.880(5) Åadjacent to the lone pair] supports this possibility.[15] Such anenvironment leaves space for close contacting of another atomsof perchlorate anions. To find any potential donor center, it isnecessary to extend the bonding limit. If a limit of 3.35 Å wasto be placed upon PbII donor atoms separation regarded asinvolving in coordination bonding, the Pb1 atoms are closecontacted by two oxygen atoms of perchlorate anions with dis-tances of Pb2···O4 = 3.511 and Pb2···O4i = 3.445 Å.[16]

The lead(II) atoms are bridged by two azide ions in a μ2-1,1 fashion with a Pb···Pb distance in the polymeric units of4.121 Å. The perchlorate anions coordinate to each lead atomas monodentate ligands and also bridge two adjacent Pb2+ ions,with a Pb···Pb separation of 4.960 Å in the polymeric units.This is the first perchlorate anion bridging ligand in a lead(II)complex. A schematic representation of the PbII environmentis shown in Figure 4.

There are three different types of noncovalent π–π stackinginteractions[17] between the parallel aromatic rings belonging

Figure 4. Schematic representation of PbII environment.

[Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n with the First Pb2-(μ-ClO4)2 Unit

to adjacent chains, as shown in Figure 5 and Figure 6. Theinterplanar distance of the “dmp” ligands (Figure 5) are 3.40,3.55, and 3.64 Å, appreciably shorter than the normal π–πstacking.[18] Consequently, the π–π stacking interactions alsoallow the 1D structure to form a 3D network (Figure 6).

Figure 5. Projection of the nearest neighboring pairs π–π stacks ofheteroaromatic bases in [Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n.

Figure 6. Packing of 1D Chains to form 3D supramolecular layers byπ–π stacking interactions.

Thus, two factors, lone pair activity and π–π stacking, maycontrol the coordination sphere of leadII ions in this complex.Subsequently, the obvious question is whether the lone pairactivity has stretched coordinate bonds to result in ligandstacking or whether it is the stacking interaction which im-poses a gap in the coordination sphere. However, one couldsay that the cooperative effect of the π–π interactions and thepresence of the lone pair give a closer packing of the solvedstructure.

DFT Calculations

The calculated structural parameters are listed in Table 2. Itshould be noted that the experimental data belong to the solidphase, whereas the calculated data correspond to the isolatedmolecule in gas-phase. However, the experimental and compu-tational data in Table 2 clearly show that both data onlyslightly differ from each other. For example, the largest differ-ence between experimental and calculated O2–Pb1 length isabout 0.066 Å, whereas the largest deviation of ca. 5.73° oc-

Z. Anorg. Allg. Chem. 2012, 844–850 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 847

curs for the N3i–Pb2–O2i angle. As a result, the calculatedgeometrical parameters represent a good approximation.

Table 2. Selected bond lengths /Å and angles /° for [Pb2(dmp)2(μ-N3)2-(μ-ClO4)2]n (experimental data belong to the solid phase, whereas thecalculated data correspond to the isolated molecule in gas-phase).

Experimental Calculated

Pb2···Pb1i 4.960 5.004N1–Pb2 2.528(5) 2.532N2–Pb2 2.558(6) 2.594N3–Pb2 2.393(5) 2.407N3i–Pb2 2.602(7) 2.668O1–Pb2 2.880(5) 2.998O2i–Pb2 2.873(4) 2.990Pb1···Pb2 4.121 4.189N2–Pb2–N1 83.48(17) 85.23N3–Pb2–N3i 67.61(16) 69.50O2–Pb2–O2i 109.74(12) 112.10O1–Pb2–N3 77.13(13) 80.15O1–Pb2–N1 104.72(10) 105.12N2–Pb2–O1 160.67(12) 163.56N3i–Pb2–O2i 164.29(12) 170.02N3–Pb2–O2i 128.17(12) 130.45O2i–Pb2–N1 91.72(12) 96.43O2i–Pb2–N2 93.63(12) 99.16

The computed IR frequencies are listed in Table 1 togetherwith the experimentally determined frequencies. The assign-ment of the ν(Pb–N) vibration is based on the theoreticallycalculated frequency with the frequency value 390 cm–1 for alead complex [Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n.

The NBO charges of lead(II) and of the coordinated atomswere also calculated. The positive charge of the lead(II) ionswas 1.359. The charges of the nitrogen atoms of the “dmp”ligands were –0.524 and –0.510, respectively, whereas the ni-trogen atoms of both azide anions (N4i and N4) have similarcharges: N4i = –0.875 and N4 = –0.876. The charges of thecoordinated oxygen atoms of the perchlorate were –0.799 and–0.875.

The calculations indicate that complex 1 has 87 occupiedmolecular orbitals (MOs) per [Pb(dmp)(μ-N3)(μ-ClO4)] unit.The value of the energy separation between the highest occu-pied molecular orbital (HOMO) and the lowest unoccupiedmolecular orbital (LUMO) was calculated. Figure 7 shows theHOMO and LUMO for the lead(II) complex. As can be seenin Figure 7, the HOMO of the title complex is principally lo-calized on the “dmp” ligand, whereas the LUMO is approxi-mately delocalized on two nitrogen atoms of the azide anionand four oxygen atoms of perchlorate anion including lead(II).The calculated HOMO-LUMO gap is 3.026 eV. Comparedwith lead azide [Pb(N3)2] gap (4.7 eV),[9] [Pb(dmp)(N3)2]n gap(1.662 eV),[10b] and [Pb(dmp)(μ-N3)(μ-NO3)]n

[10c] gap(3.148 eV), it was found that the complex 1 gap is betweenthat of [Pb(N3)2] and [Pb(dmp)(N3)2]n and comparable with[Pb(dmp)(μ-N3)(μ-NO3)]n. Therefore, complex 1 is expectedto be a primary explosive and to be moderately sensitive toshock.[9,11]

B. Shaabani et al.ARTICLE

Figure 7. Frontier molecular orbitals for a unit of [Pb(dmp)(μ-N3)-(μ-ClO4)].

Nanostructure of PbO

Nanopowders of PbO were generated by thermal decompo-sition of nanorods of compound 1 in an air atmosphere. Thepowder XRD pattern (Figure 8), matches the standard patternof orthorhombic PbO with a = 5.8931 Å and z = 4 (JCPDScard file No. 77–1971). The morphology and size of the pre-pared PbO samples were further observed using SEM. Figure 9shows a SEM image of the PbO nanopowders. Calcination ofthe bulk powder of 1 produces regularly shaped PbII oxidenanoparticles with a diameter of about 23 nm (Figure 9).

Figure 8. XRD patterns of PbO after calcination of 1.

Conclusions

In this work, a novel 1D PbII coordination polymer contain-ing a versatile bridging ligand (azide anion) and a perchlorateanion bridging ligand is described together with a simple sono-

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Figure 9. SEM photographs of PbO nanopowders (produced by calci-nation of nanorods).

chemical preparation of nanostructures of this coordinationpolymer and its use in the preparation of PbO nanoparticles.The crystal structure of the complex was also determined,which indicates that it takes the form of a one dimensionalpolymer in the solid state. The arrangement of the ligands sug-gests a gap in the coordination environment around the metalions possibly occupied by a “stereo-active” lone pair of elec-trons on lead(II). Two factors, lone pair activity and π–π stack-ing, may control the coordination sphere of lead(II) ions in thiscomplex. A theoretical study of the title perchlorato-lead(II)-azido complex was undertaken to examine its electronic struc-ture, which allowed computations of bond lengths and anglesand vibrational frequencies in good agreement with the experi-mental data.

Experimental Section

Materials and Physical Measurements: All chemicals were obtainedfrom commercial sources and used as received. A multiwave ultrasonicgenerator (Sonicator-3000; Misonix Inc., Farmingdale, NY, USA),equipped with a converter/transducer and titanium oscillator (horn),12.5 mm in diameter, operating at 20 kHz with a maximum poweroutput of 600 W at room temperature for 1 h, was used for the ultra-sonic irradiation. Infrared spectra were recorded from KBr pellets witha Perkin–Elmer 883-IR spectrophotometer and with a Nicolet 520FTIR spectrophotometer. Elemental analyses (C, H, N) were per-formed with a Perkin–Elmer 2400 II elemental analyzer. X-ray powderdiffraction (XRD) measurements were performed with an X’pert dif-fractometer manufactured by the Panalytical company, with monochro-matized Cu-Kα radiation and simulated XRD powder patterns basedon single crystal data were prepared using the Mercury program.[12]

The crystallite sizes of selected samples were estimated using theScherrer formula. The samples were characterized with a scanningelectron microscope with gold coating. Melting points were measuredwith an Electrothermal 9100 apparatus and are uncorrected. 1H NMRand 13C NMR spectra were measured with a BRUKER DRX-500 AV-ANCE spectrometer at 500 MHz, respectively.

Preparation of [Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n (1): To prepare thenanostructure of [Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n (1), Pb(ClO4)2 (15 ml,

[Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n with the First Pb2-(μ-ClO4)2 Unit

0.1 m solution in H2O) was positioned in a high-density ultrasonicprobe, operating at 20 kHz with a maximum power output of 600 W.Into these solution the ligands 2,9-dimethyl-1,10-phenanthroline(15 ml, 0.1 m solution) and sodium azide (22 mL, 0.1 m solution) wereadded dropwise. The obtained precipitates were filtered off, washedwith water and finally dried in air. M.p. 243 °C. Analysis forC28H24Cl2N10O8Pb2: calcd. C 30.19, H 2.17, N 12.57%; found C30.20, H 2.20, N 13.00%. IR (KBr, selected bands): ν̃ = 610 m, 675m, 824 s, 1130 vs. (–ClO4), 1330 m (νsym of –N3), 1470 s and 1515 s(aromatic ring), 2055 vs. (νasym of μ-1,1-N3), 2065 vs. (νasym of μ-1,1-N3), 2992 m, 3058 w[13] cm–1.

To isolate single crystals of [Pb2(dmp)2(μ-N3)2(μ-ClO4)2]n (1), 2,9-di-methyl-1,10-phenanthroline (0.20 g, 1 mmol) was placed in one armof a branched tube and a solution of hydrated Pb(ClO4)2 (1 mmol,prepared by dissolving the appropriate amount of PbCO3 in the mini-mum volume of 70% HClO4) and sodium azide (0.130 g, 2 mmol) inthe other. Methanol was carefully added to fill both arms, the tubesealed and the ligand-containing arm immersed in a bath at 60 °C,while the other was left at ambient temperature. After three weeks,crystals (m.p. 245 °C) suitable for X-ray structure determination haddeposited in the arm at ambient temperature. Subsequently, they werefiltered off, washed with acetone and ether, and air dried. Yield 55%.Analysis for C28H24Cl2N10O8Pb2: calcd. C 30.19, H 2.17, N 12.57%;found C 30.05, H 2.15, N 12.60%. IR (KBr, selected bands): ν̃ = 615m, 675 m, 825 s, 1130 vs. (–ClO4), 1330 m (νsym of –N3), 1470 s and1515 s (aromatic ring), 2055 vs. (νasym of μ-1,1-N3), 2065 vs. (νasym

of μ-1,1-N3), 2994 m, 3058 w[13] cm–1. 1H NMR (DMSO,): δ = 2.75(s, 6 H, methyl-H), 8.35 (d, 2 H, py-H), 7.90 (d, 2 H, py-H), 7.75 (s,2 H, py-H) ppm. 13C NMR (DMSO): δ = 28 (methyl), 125 (py), 128(py), 130 (py), 138 (py), 143 (py), 160 (py) ppm.

Crystallography: Crystallographic data were collected at 100 K withthe Oxford Xcalibur CCD area detector diffractometer, using graphitemonochromatic Mo-Kα (λ = 0.71069Å) radiation. Data reduction andabsorption correction were performed using CrysAlis RED 1.171.26(Oxford Diffraction). The structure was solved by direct methods usingSIR2004[19a] and refined by full-matrix least-squares using SHELX-97.[19b] Hydrogen atoms were generated in calculated position usingSHELX-97.[19b] Materials for publication were prepared usingSHELXTL[19b] and ORTEP-III.[19c]

Crystallographic data (excluding structure factors) for the structure inthis paper have been deposited with the Cambridge CrystallographicData Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copiesof the data can be obtained free of charge on quoting the depositorynumber CCDC-798926 (Fax: +44-1223-336-033; E-Mail: deposit@-ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).

Computational Details: The arrangement of the [Pb2(dmp)2(μ-N3)2-(μ-ClO4)2]n complex was optimized using the B3LYP density func-tional model.[20] In these calculations we used the 3-21G* basis set forC and H atoms, while the 6-31G* basis set was used for nitrogen,oxygen, and chlorine atoms. For the lead atoms, the LanL2DZ valenceand effective core potential functions were used.[21a] All DFT calcula-tions were performed by using the Gaussian 98 R-A.9 package.[21b] X-ray structures were used as input geometries when available.

Acknowledgement

The authors acknowledge financial support by University of TabrizResearch Council (project number sad/27/1391-3). HKF would like to

Z. Anorg. Allg. Chem. 2012, 844–850 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 849

thank the Malaysian Government and Universiti Sains Malaysia forthe Research University Golden Goose Grant 1001/PFIZIK/811012.

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[14] Crystal data for compound 1: C28H24Cl2N10O8Pb2, Mr = 1113.85,monoclinic, space group C2/C, a = 30.2742(8), b = 12.6047(3), c= 21.6575(10) Å, β = 127.3680(10)°, V = 6568.2(4) Å3, Dc (Z =8 f. u.) = 2.253 Mg·m–3, F(000)= 4192. Specimen:0.82�0.13�0.08 mm; R(wR) = 0.0446 (0.1224) for 12219 re-flections with I � 2σ(I).

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[21] a) P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 270–283; b)A description of the basis sets and theory level used in this workcan be found in the following: J. B. Foresman, A. E. Frisch, Ex-ploring Chemistry with Electronic Structure Methods, 2nd ed.,Gaussian Inc., Pittsburgh, PA, 1996.

Received: November 10, 2011Published Online: February 28, 2012