Journal of Molecular Structure 994 (2011) 321–324

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Journal of Molecular Structure

journal homepage: www.elsevier .com/ locate /molst ruc

Synthesis, structure and properties of Pb2Bi2AlB3O11

Junjie Li a,b, Shilie Pan a,⇑, Wenwu Zhao a,b, Xuelin Tian a, Jian Han a, Xiaoyun Fan a

a Xinjiang Key Laboratory of Electronic Information Materials and Devices, Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Sciences,40-1 South Beijing Road, Urumqi 830011, Chinab Graduate School of the Chinese Academy of Sciences, Beijing 100039, China

a r t i c l e i n f o a b s t r a c t

Article history:Received 8 December 2010Received in revised form 19 March 2011Accepted 21 March 2011Available online 24 March 2011

Keywords:Pb2Bi2AlB3O11

BorateStructure determinationSingle-crystal diffraction

0022-2860/$ - see front matter � 2011 Elsevier B.V. Adoi:10.1016/j.molstruc.2011.03.042

⇑ Corresponding author. Tel.: +86 991 3674558; faxE-mail address: slpan@ms.xjb.ac.cn (S. Pan).

Single crystals of Pb2Bi2AlB3O11 were grown from a PbO/Bi2O3/Al2O3/H3BO3/PbF2 flux. The single-crystalX-ray structural analysis showed that Pb2Bi2AlB3O11 crystallizes in the monoclinic space group C2/c (No.15) with a = 17.263(2) Å, b = 8.7322(11) Å, c = 6.8081(9) Å, a = 90�, b = 90.566(2)�, c = 90�, Z = 4 andR1 = 0.0393, wR2 = 0.1013. Its structure may be described as three-dimensional frameworks formed of(1 0 0) [Pb6Bi6Al3O6]1 layers stacked along a-axis. The layers are interconnected via BO3 groups. TheIR spectrum further confirmed the presence of BO3 groups in the structure. The thermal analysis suggeststhat Pb2Bi2AlB3O11 is a congruently melting compound.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction

Borates have long been a remarkable source of nonlinear optical(NLO) materials, such as b-BaB2O4 (BBO) and LiB3O5 (LBO) [1].Lead-containing borates are of considerable interest because thepresence of Pb2+ 6s2 electron lone pair is favorable for the forma-tion of noncentrosymmetrical crystalline phases, which is a pre-requisite for a variety of technologically important propertiesincluding ferroelectricity, piezoelectricity, pyroelectricity, and sec-ond-order nonlinear optical behavior [2]. For example, in the bin-ary PbO–B2O3 system, PbB4O7 has been the most extensivelystudied because it is a piezoelectric and NLO material that has po-tential application in design and fabrication of electronic, acoustic,and optical devices [3]. So far, many investigations have been doneon the binary lead borates, while the complex borates incorporat-ing lead together with other metal elements are relatively less ex-plored. Only several anhydrous ternary compounds, i.e.,Pb2Cu3B4O11 [4], Pb2Cu(BO3)2 [5], PbMBO4 (M = Cr, Mn, Fe, Al, Ga,Bi) [6–9], and (Pb3O)2(BO3)2MO4 (M = Cr, Mo) [10], have been re-cently structurally characterized. We are interested in the Pb-con-taining and Bi-containing borates, because Bi3+ also has 6s2

electron lone pair like Pb2+, both BiOn and PbOn groups have verysimilar coordination configuration, and some interesting materialsmay be expected to exist in the Pb- and Bi-containing borates.Based on the above consideration, we investigated the quaternarysystem of PbO–Bi2O3–Al2O3–B2O3, and a new lead and Bi-contain-ing borate compound, Pb2Bi2AlB3O11, was found. Herein we de-

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scribe its syntheses, crystal structure, the thermal stability andinfrared spectrum.

2. Experiment

2.1. Sample preparation and general characterization

All reagents used in the synthesis were of analytical grade.Small single crystals of Pb2Bi2AlB3O11 were obtained from the meltof PbO:Bi2O3:Al2O3:H3BO3:PbF2 with molar ratio of 2:1:1:2:1.According to the ratio, the raw materials of 10.830 g PbO,11.305 g Bi2O3, 2.474 g Al2O3, 3.000 g H3BO3 and 5.949 g PbF2 weremelted at 760 �C in a platinum crucible that was placed into a ver-tical, programmable temperature growth furnace. It was held atthat temperature for 10 h, slowly cooled to 400 �C at a rate of5 �C/h, and finally cooled to room temperature at a rate of 10 �C/h. Single crystals of Pb2Bi2AlB3O11 were obtained for further char-acterization by single-crystal X-ray diffraction measurements. Sub-sequently, direct reaction of a stoichiometric mixture of PbO, Bi2O3,Al2O3 and H3BO3 at 650 �C for 40 h with an intermediate grindingyielded a single-phase polycrystalline sample of Pb2Bi2AlB3O11 thatwas confirmed by powder X-ray diffraction analysis using themonochromatized Cu Ka radiation of a Bruker D8 ADVANCE dif-fractometer (see Fig. S1 in the supporting information). Infraredspectrum was recorded on a Bruker Equinox 55 Fourier transforminfrared spectrophotometer. The sample was mixed thoroughlywith dried KBr (5 mg of the sample and 500 mg of KBr), and thespectrum was collected in a range from 400 to 4000 cm�1 with aresolution of 2 cm�1. The thermal analysis was carried out on asimultaneous Netzsch STA 449C thermal analyzer instrument, with

Table 2Bond lengths (Å) and angles (�) for Pb2Bi2AlB3O11.

Atoms Distances Atoms Angles

Bi(1)–O(2) 2.162(8) O(2)–Bi(1)–O(6) 82.7(4)Bi(1)–O(6) 2.188(11) O(2)–Bi(1)–O(5) 81.0(3)Bi(1)–O(5) 2.369(7) O(6)–Bi(1)–O(5) 83.2(4)Bi(1)–O(3)#1 2.375(10) O(2)–Bi(1)–O(3)#1 67.6(3)Bi(1)–O(4)#1 2.451(10) O(6)–Bi(1)–O(3)#1 90.1(4)Pb(1)–O(4) 2.304(10) O(5)–Bi(1)–O(3)#1 148.5(3)Pb(1)–O(1) 2.375(10) O(2)–Bi(1)–O(4)#1 72.1(3)Pb(1)–O(2)#2 2.379(9) O(6)–Bi(1)–O(4)#1 154.4(4)Pb(1)–O(2)#1 2.465(9) O(5)–Bi(1)–O(4)#1 88.2(4)Al(1)–O(3)#1 1.858(9) O(3)#1–Bi(1)–O(4)#1 84.8(4)

322 J. Li et al. / Journal of Molecular Structure 994 (2011) 321–324

a heating rate of 2.5 �C min�1 in an atmosphere of flowing N2 from25 to 900 �C.

2.2. Structure determination

A transparent and colorless crystal of Pb2Bi2AlB3O11 withdimensions 0.264 � 0.168 � 0.083 mm3 was chosen for structuredetermination by single-crystal X-ray diffraction on a BrukerSMART APEX II 4K CCD diffractometer using monochromaticMo Ka radiation (k = 0.71073 Å) and integrated with the SAINT—Plus program [11].

Al(1)–O(3) 1.858(9) O(4)–Pb(1)–O(1) 91.6(4)Al(1)–O(2)#1 1.860(9) O(4)–Pb(1)–O(2)#2 76.6(3)Al(1)–O(2) 1.860(9) O(1)–Pb(1)–O(2)#2 80.2(3)Al(1)–O(1) 1.968(10) O(4)–Pb(1)–O(2)#1 69.6(3)Al(1)–O(1)#1 1.968(10) O(1)–Pb(1)–O(2)#1 65.3(3)Al(1)–Bi(1)#1 3.1913(7) O(2)#2–Pb(1)–O(2)#1 129.9(3)B(1)–O(4) 1.345(14) O(3)#1–Al(1)–O(3) 180.000(1)B(1)–O(4)#3 1.345(14) O(3)#1–Al(1)–O(2)#1 94.3(4)B(1)–O(5)#4 1.42(3) O(3)–Al(1)–O(2)#1 85.7(4)B(2)–O(6) 1.354(18) O(3)#1–Al(1)–O(2) 85.7(4)B(2)–O(3)#2 1.377(17) O(3)–Al(1)–O(2) 94.3(4)B(2)–O(1) 1.377(17) O(2)#1–Al(1)–O(2) 180.0(3)

O(3)#1–Al(1)–O(1) 89.0(4)O(3)–Al(1)–O(1) 91.0(4)O(2)#1–Al(1)–O(1) 86.0(4)O(2)–Al(1)–O(1) 94.0(4)O(3)#1–Al(1)–O(1)#1 91.0(4)O(3)–Al(1)–O(1)#1 89.0(4)O(2)#1–Al(1)–O(1)#1 94.0(4)O(2)–Al(1)–O(1)#1 86.0(4)O(1)–Al(1)–O(1)#1 180.000(1)O(4)–B(1)–O(4)#3 122.6(18)O(4)–B(1)–O(5)#4 118.7(9)O(4)#3–B(1)–O(5)#4 118.7(9)O(6)–B(2)–O(3)#2 116.8(12)O(6)–B(2)–O(1) 122.5(12)O(3)#2–B(2)–O(1) 120.7(12)

Symmetry transformations used to generate equivalent atoms:#1 �x + 3/2, �y + 1/2, �z + 2; #2 �x + 3/2, y + 1/2, �z + 3/2; #3 �x + 2, y, �z + 3/2;#4 x + 1/2, y + 1/2, z; #5 �x + 3/2, y � 1/2, �z + 3/2; #6 x � 1/2, y � 1/2, z; #7 �x + 1,y, �z + 3/2.

3. Results and discussion

3.1. Crystal structure

The single-crystal X-ray structural analysis showed thatPb2Bi2AlB3O11 crystallizes in the monoclinic space group C2/c(No. 15). All calculations were performed with programs fromthe SHELXTL-97 crystallographic software package [12]. The struc-ture was solved by direct methods. Equivalent reflections werethen averaged. Final least-squares refinement is on F2

0 with datahaving F2

0 P 2r(F20). The reliability factors converged to

R1 = 0.0393, and wR2 = 0.1013. Crystal data and structure refine-ment information are summarized in Table 1. Final atomic coordi-nates and equivalent isotropic displacement parameters are listedin Table S1 in the supporting information. Selected interatomic dis-tances and angles are given in Table 2.

The bond valence sums of each atom in Pb2Bi2AlB3O11 were cal-culated [13,14] and are listed in Table 3. These valence sums agreewith the expected oxidation states [15–17].

Polyhedral representation of Pb2Bi2AlB3O11 is shown in Fig. 1. Inthe structure, six unique oxygen atoms can be classified into threegroups depending on their coordinate environments: The O(6)atom is two coordinate, connects to Bi(1) and B(2) atoms. TheO(1), O(3), O(4) and O(5) atoms are three coordinate. The O(1)atom is coordinated to Pb(1), Al(1) and B(2) atoms; The O(3) atom

Table 1Crystal data and structure refinement for Pb2Bi2AlB3O11.

Empirical formula Pb2Bi2AlB3O11

Formula weight 1067.75Temperature 296(2) KWavelength 0.71073 ÅCrystal system MonoclinicSpace group C2/cUnit cell dimensions a = 17.263(2) Å, a = 90�

b = 8.7322(11) Å, b = 90.566(2)�c = 6.8081(9) Å, c = 90�

Volume 1026.2(2) Å3

Z 4Calculated density 6.911 g/cm�3

Absorption coefficient 67.044 mm�1

F(0 0 0) 1784Crystal size 0.264 � 0.168 � 0.083 mm3

Theta range for data collection 2.61–27.63�Limiting indices �21 6 h 6 21, �11 6 k 6 11, �7 6 l 6 8Reflections collected/unique 383/1191 [R(int) = 0.0457]Completeness to theta = 27.39 98.80%Refinement method Full-matrix least-squares on F2

Data/restraints/parameters 1191/18/90Goodness-of-fit on F2 1.117Final R indices [I > 2s(I)]a R1 = 0.0393, wR2 = 0.1013R indices (all data)a R1 = 0.0425, wR2 = 0.1032Extinction coefficient 0.00088(10)Largest diff. peak and hole 6.063 and �2.642 e �3

a R1 =P

||F0| � |Fc||/P

|F0| and wR2 = [P

w(F20 � F2

c )2/P

wF40]1/2 for F2

0 > 2rðF20Þ,

w = 1/[r2(F20) + (0.0455P)2 + 61.9651P], where P = (F2

0 þ 2F2c )/3.

Table 3Bond valence analysis of the Pb2Bi2AlB3O11.a,b

Atom Pb(1) Bi(1) Al(1) B(1) B(2)P

Anions

O(1) 0.491 0.390[�2] 0.987 1.865O(2) [�2]0.486[�2] 0.832 0.523[�2] 2.327O(3) 0.468 0.526[�2] 0.984 1.981O(4) 0.595 0.381 1.073[�2] 2.049O(5) [�2]0.476 0.876 1.828O(6) 0.776 1.047 1.823P

Cations 2.058 2.933 2.878 3.022 3.015

a Bond valences calculated with the program Bond Valence Calculator Version2.00, Hormillosa, C., Healy, S., Stephen, T. McMaster University (1993).

b Valence sums calculated with the formula: Si = exp[(R0 � Ri)/B], where Si = va-lence of bond ‘‘i’’ and B = 0.37. Left and right superscripts indicate the number ofequivalent bonds for cations and anions, respectively.

is coordinated to Bi(1), Al(1) and B(2) atoms; The O(4) atom iscoordinated to Pb(1), Bi(1) and B(1) atoms; The O(5) atom is coor-dinated to Bi(1), Bi(1) and B(1) atoms. The O(2) atom is four coor-dination, bonds to Pb(1), Pb(1), Bi(1) and Al(1) atoms to form O-centered tetrahedra. The OPb2BiAl tetrahedra share corners to formtwo-dimensional [Pb6Bi6Al3O6]1 layers paralleled to the (1 0 0)plane (see Fig. 1a). The stacking mode of [Pb6Bi6Al3O6] layers isshown in Fig. S3 in the support information. The unit of [Pb6Bi6A-l3O6]27+ is shown in Fig. S4 in the support information. BO3 groups

c

b

b

a

(a)

(b)

Fig. 1. (a) Two-dimensional [Pb6Bi6Al3O6]1 layers paralleled to the (1 0 0) plane; (b) the three-dimensional frameworks in Pb2Bi2AlB3O11. The green tetrahedra are OPb2BiAlgroups. The green spheres are O atoms; the blue spheres are B atoms; the dark blue spheres are Al atoms; the pink spheres are Pb atoms; the red spheres are Bi atoms. (Forinterpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

500 600 700 800 900

-10

-5

End

o

Tem

pera

ture

Dif

fere

nce

Temperature (oC)

Fig. 2. DSC curve of Pb2Bi2AlB3O11.

J. Li et al. / Journal of Molecular Structure 994 (2011) 321–324 323

that are stacked along the c-axis in a staggered form are interactedwith the [Pb6Bi6Al3O6]1 layers via Pb–O [2.304(10)–2.375(10) Å],Bi–O [2.369(7)–2.451(10) Å] and Al–O [1.858(9)–1.968(10) Å]bonds to complete the final three-dimensional frameworks result-ing in the formula Pb2Bi2AlB3O11 (see Fig. 1b).

3.2. FT-IR spectrum

To investigate the coordination environment of B atom, theinfrared spectrum was measured at room temperature and shownin Fig. S2 in the support information. Absorption peaks were as-signed from literature precedents [18,19]. The strong bands at1220 and 1274 cm�1 arise from BO3 antisymmetric stretchingvibrations and those at 708, 702 and 667 cm�1 are mainly due tothe out-of plane bending of B–O in BO3. The bands between 491and 590 cm�1 can be attributed to the in-plane bending of B–Oin BO3. The IR spectra further confirmed the existence of trigonallycoordinated boron atoms, consistent with the single-crystal X-raystructural analysis.

3.3. Thermal behavior

The DSC curve of Pb2Bi2AlB3O11 is shown in Fig. 2. It shows oneendothermic peak at 693 �C on the heating curve, which tenta-

tively suggests that Pb2Bi2AlB3O11 melts congruently at 678 �C.To verify that Pb2Bi2AlB3O11 melts congruently, Pb2Bi2AlB3O11

compound powder (4 g) was heated to 700 �C, and then slowlycooled to room temperature. Analysis of the powder XRD patternof the solidified melt revealed that the solid product exhibited adiffraction pattern identical to that of the initial Pb2Bi2AlB3O11

powder (see Fig. 3), further demonstrating that Pb2Bi2AlB3O11 is acongruently melting compound.

10 20 30 40 50 602θ (deg)

sample after meltingsample before melting

Inte

nsit

y (a

.u.)

Fig. 3. X-ray powder diffraction pattern of the Pb2Bi2AlB3O11 samples before andafter melting, respectively.

324 J. Li et al. / Journal of Molecular Structure 994 (2011) 321–324

4. Conclusions

In this work we have obtained a new compound Pb2Bi2AlB3O11

from PbO–Bi2O3–Al2O3–H3BO3–PbF2 mixture by solid-state reac-tion, and solved its structure from single-crystal diffraction data.Pb2Bi2AlB3O11 may be described as three-dimensional frameworksformed of (1 0 0) [Pb6Bi6Al3O6]1 layers stacked along a axis. Thelayers are interconnected via BO3 groups. Meanwhile, we investi-gated the infrared spectrum of the title compound, and found thatit was consistent with the crystallographic study. Finally, the ther-mal stability was studied, which suggested that Pb2Bi2AlB3O11 is acongruently melting compound.

Acknowledgments

This work is supported by Main Direction Program of Knowl-edge Innovation of Chinese Academy of Sciences (Grant No.KJCX2-EW-H03-03), the ‘‘National Natural Science Foundation ofChina’’ (Grant Nos. 50802110, 21001114), the ‘‘One Hundred Tal-ents Project Foundation Program’’ of Chinese Academy of Sciences,the ‘‘Western Light Joint Scholar Foundation’’ Program of ChineseAcademy of Sciences, the ‘‘High Technology Research and Develop-

ment Program’’ of Xinjiang Uygur Autonomous Region of China(Grant No. 200816120) and Scientific Research Program of Urumqiof China (Grant No. G09212001).

Appendix A. Supplementary data

An X-ray crystallographic file in CIF format including crystallo-graphic details; atomic coordinates (�104) and equivalent isotropicdisplacement parameters (Å2 � 103) for Pb2Bi2AlB3O11; experimen-tal and calculated XRD patterns; IR spectrum of the Pb2Bi2AlB3O11;the stacking layers of [Pb6Bi6Al3O6] and the unit of [Pb6Bi6A-l3O6]27+. Supplementary data associated with this article canbe found, in the online version, at doi:10.1016/j.molstruc.2011.03.042.

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