Inorganic Chemistry Communications 40 (2014) 168–171

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Inorganic Chemistry Communications

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Synthesis, structure and properties of a newnoncentrosymmetric aluminoborate

Qin Meng a, Guo-Ming Wang b,⁎, Bai-Feng Yang a, Huan He a, Guo-Yu Yang a,c,⁎⁎a MOE Key Laboratory of Cluster Science, School of Chemistry, Beijing Institute of Technology, Beijing 100081, Chinab Teachers College, College of Chemistry and Environment of Qingdao University, Shandong 266071, Chinac State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China

⁎ Corresponding author. Tel./fax: +86 10 68918572.⁎⁎ Correspondence to: G.-Y. Yang, MOE Key LaboratorChemistry, Beijing Institute of Technology, Beijing 100081, C

E-mail addresses: gmwang_pub@163.com (G.-M. Wygy@fjirsm.ac.cn (G.-Y. Yang).

1387-7003/$ – see front matter © 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.inoche.2013.12.005

a b s t r a c t

a r t i c l e i n f o

Article history:Received 6 November 2013Accepted 4 December 2013Available online 12 December 2013

Keywords:AluminoborateNonlinear opticalSolvothermal synthesisCrystal structure

A new noncentrosymmetric aluminoborate (H2TETA)[Al(B5O10)] (1), has been solvothermally synthesized byusing triethylenetetramine (TETA) as the structure-directing agent. Single-crystal X-ray diffraction analysisreveals that the compound crystallizes in the orthorhombic space group Pna21 with unit cell parametersa = 12.9696(9) Å, b = 17.0035(8) Å, c = 7.3660(5) Å, V = 1624.41(18) Å3 and Z = 4. Its structure consistsof AlO4 tetrahedra and B5O10 clusters and possesses 8-, 11- and 14-ring channels with sra topology. Second-harmonic generation (SHG) measurements on the powder samples reveal that 1 exhibits moderate SHG signalsapproximately 1.5 times that of KH2PO4 (KDP).

© 2013 Elsevier B.V. All rights reserved.

Crystalline borate materials are of great interest due to their diversestructural chemistry and promising applications in mineralogy, lumi-nescence and nonlinear optical (NLO) materials [1]. From the perspec-tive of structure, the flexibility of boron to adopt both BO3 and BO4

coordination modes, together with the propensity of such groups topolymerize into awide range of polyanions, offers greater opportunitiesin making new borates with structural and compositional complexity[2]. A particular driving force in this area is to synthesize new solidswith acentric structures and NLO properties [3]. Compared to only 15%of inorganic crystals crystallizing in acentric space groups, more than35% of known borates are featured with acentric structures [4], whichmay provide an ideal candidate for pursuing borate NLO materials.β-BaB2O4 (BBO), LiB3O5 (LBO) and Sr2Be2B2O7 (SBBO), for example, rep-resent typical B-containing materials with excellent NLO activities [5].Recently, attempts to introduce heteroatoms into borate backboneshave also resulted in some intriguing systems, such as borophosphates,borogermanates, galloborates and zincoborates, etc. [6–9]. In the specif-ic field of aluminoborates, the compositional Al element has more flex-ible coordination modes (AlO4: tetrahedral, AlO5: square–pyramidal ortrigonal–bipyramidal, and AlO6: octahedral), and a series of new mate-rials with novel topologies and useful properties have been successfullysynthesized throughdifferent synthetic approaches [10]. Notable exam-ples include porous frameworks of PKU-1 and PKU-2 with extra-large

y of Cluster Science, School ofhina. Tel./fax:+ 861068918572.ang), ygy@bit.edu.cn,

ghts reserved.

pores of 18- and 24-ring channels [11], multimetal-centered borateclusters PKU-8 and QD-6 [12], as well as a very few cases with helicalchannels [13].

One important reason for our interest in this area is to design and syn-thesize new aluminoborates with acentric structural features and NLOproperties. It has been demonstrated that the simultaneous introductionof Al components into pure borate frameworks may greatly increase thelikelihood of producing acentric structures, especially when the acentricB\O clusters were combined with the chiral Al center, i.e. four-coordinated AlO4 groups. On the basis of the above consideration,we suc-cessfully obtained a new organically templated aluminoborate, (H2TETA)[Al(B5O10)] (1), which is constructed fromAlO4 and B5O10 groups and ex-hibits a noncentrosymmetric three-dimensional architecture.

Compound 1 was synthesized by the solvothermal reaction ofAl(i-PrO)3, H3BO3, triethylenetetramine and pyridine at 180 °C for7 days [14]. Note that 1 appeared to be only achieved in the absenceof water; otherwise, a known polyborate [C6N4H20]0.5·[B5O6(OH)4][15] would be obtained when pyridine and water were used as thesolvent under similar conditions. The structure of 1 was characterizedby single-crystal X-ray diffraction, elemental analysis, IR and thermo-gravimetric analysis. The purity of the crystalline solid was verified bythe powder XRD (Fig. 1).

Single crystal X-ray analysis [16] reveals that 1 crystallizes in theorthorhombic space group Pna21, and the asymmetric unit containsone independent Al atom, one unique B5O10 unit and one diprotonatedH2TETA cation. As depicted in Fig. 2, the unique Al atom adopts tetrahe-dral geometry with Al\O bond lengths varying from 1.711(4) to1.743(6) Å and O\Al\O bond angles changing from 108.5(2) to

Fig. 1. Experimental and simulated powder X-ray diffraction patterns of 1.

Fig. 3. (a, b) Views of the linkage of B5O10 and AlO4 groups in 1. Each B5O10/AlO4 unit isbridged by four AlO4/B5O10 groups to 10 other B5O10/AlO4 units. Color code: B5O10 cluster,red; AlO4, green.

169Q. Meng et al. / Inorganic Chemistry Communications 40 (2014) 168–171

112.8(3)°. The B5O10 cluster is made up of one BO4 tetrahedron and fourBO3 triangles, inwhich two planar B3O3 rings are perpendicularly linkedby the common B(3)O4 tetrahedron. The B\O bond lengths are in theregion of 1.326(8)–1.481(9) Å and O\B\O bond angles are distributedin the range of 116.8(6)–123.0(5)° and 106.7(5)–111.0(4)° for BO3 andBO4 units, respectively.

The alternate connectivity between the B5O10 clusters and the AlO4

tetrahedra through their vertices creates a three-dimensional architecturewith multidirectional channels. In this structure, each B5O10 cluster isconnected to 10 neighboring B5O10 clusters through four bridging AlO4

groups, and each AlO4 group is also connected to 10 neighbors throughfour bridging B5O10 clusters (Fig. 3). Thus, no Al\O\Al connection existsin the structure. Fig. 4a shows the regular 8- and 14-ring channels vieweddown the [010] direction. The largest 14-ring channels are ellipticalin shape and delimited by four AlO4, two BO4 and eight BO3 units in thelinkage of the \AlO4\BO3\BO4\BO3\AlO4\BO3\BO3\AlO4\BO3\BO4\BO3\AlO4\BO3\BO3\ sequence. Similarly, the openings of the8-ring channels are made up from two AlO4, two BO4 and four BO3

units with two repeating—AlO4—BO3—BO4—BO3—linkages. The oxygen-to-oxygen dimensions of 8- and 12-ring apertures in the structure areapproximately 6.6 × 4.5 Å2 and 12.6 × 6.5 Å2, respectively.

Fig. 2. ORTEP view of the asymmetric unit of 1, showing the atom-labeling scheme and50% thermal ellipsoids.

The simultaneous presence of large odd 11-ring channels along the[100] direction is also noteworthy (Fig. 4b). Except for the recentlyreported aluminoborates with larger 13- and 15-ring channels [13d],luminescence and nonlinear optical (NLO) materials, the odd 11-ringopening is the largest and scarcely observed in ICMM6 and XA-1[8,17]. The apertures of the 11-ring channels are bound by three AlO4,two BO4 and six BO3 units with the \AlO4\BO3\BO4\BO3\AlO4\BO3\BO4\BO3\AlO4\BO3\BO3\ sequence. If the AlO4 tetrahedraand B5O10 clusters are viewed as 4-connected nodes, 1 has a familiarsra-42638 net (Fig. 4c). The H2TETA templates reside in the 14-ringchannels and interact with the framework through extensive N\H ⋯ O hydrogen bonds (Fig. 5). A void space analysis using the programPLATON indicates that these extra-framework organic cations occupy57.2% of the unit cell volume.

Considering the noncentrosymmetric structure of 1, the secondharmonic generation (SHG) measurement is carried out on the powdersample by the Kurtz–Perry method at room temperature [18]. Theintensity of the green light (frequency doubled output: λ = 532 nm)

Fig. 4. Polydedral viewof the 3D structure of 1, showing the elliptical 8- and 14-ring channelsalong the c axis (a), and the odd 11-ring channels along the a axis (b). Color code: AlO4,green; BO4 and BO3, red. (c) The sra topology of 1with 42638 net.

Fig. 5. View of the 14-ring channel occupied by two H2TETA templates. The H-bondinginteractions between the templates and framework are indicated by dotted lines.

170 Q. Meng et al. / Inorganic Chemistry Communications 40 (2014) 168–171

produced by the crystal powders exhibits a SHG efficiency about 1.5times that of the KDP (KH2PO4) powder (Fig. 6), giving further evidenceof its acentric crystal structure. Thermogravimetric analysis of 1 wasperformed under a flow of air atmosphere to investigate its thermalstability (Fig. S1). The gradual weight loss of 4.36% occurred before265 °C, which may be attributed to the departure of absorbed wateron the solid sample. On further heating, the major weight loss between265 and 830 °C was observed and assigned to the removal of the guestTETA molecules (observed, 38.06%; calcd: 38.26%).

In summary, a new aluminoborate (H2TETA)[Al(B5O10)] (1), hasbeen synthesized under solvothermal condition. The linkage betweenAlO4 tetrahedra and B5O10 clusters creates a noncentrosymmetric 3Darchitecture containing 8-, 11- and 14-ring channels with sra topology.This compound possesses an SHG efficiency of about 1.5 times that ofKDP. Considered the possible cooperative effect of π-conjugated trian-gular BO3 groups and chiral AlO4 units in this system, it would be highlypromising to realize other novel aluminoborates with excellent NLOproperties. Further investigation on this subject is in progress.

Acknowledgements

Thisworkwas supported by theNNSF of China (91122028, 21221001and 50872133), the NNSF for Distinguished Young Scholars of China

Fig. 6. The measured SHG response of 1 with that of KDP.

(20725101), the 973 program (2014CB932101 and 2011CB932504), aProject of Shandong ProvinceHigher Educational Science and TechnologyProgram (J13LD18) and the Development Project of Qingdao Science andTechnology (13-1-4-187-jch).

Appendix A. Supplementary material

CCDC 943105 contains the supplementary crystallographic data for1. The data can be obtained free of charge from http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge CrystallographicData Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (+44)1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. The IR spectrumand TG curve are shown in the supporting information. Supplementarydata associatedwith this article can be found online at http://dx.doi.org/10.1016/j.inoche.2013.12.005.

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[14] Synthesis of1: AmixtureofAl(i-PrO3)3 (0.204 g),H3BO3 (0.186 g), triethylenetetramine(0.25 mL) and pyridine (3.5 mL) in the typical molar ratio of 1:3:1.7:44 was sealed ina Teflon-lined autoclave and heated at 180 °C for 7 days. After cooling over 24 h, thecolorless prismatic crystals of 1 was recovered by filtration, washed with distilledwater, and dried in air (20% yield based on Al). Elemental analysis (wt %) calcd for 1:

171Q. Meng et al. / Inorganic Chemistry Communications 40 (2014) 168–171

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