Inorganic Chemistry Communications 13 (2010) 789–792

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Inorganic Chemistry Communications

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Synthesis, crystal structure and properties of two antimony germanate compounds

Bing Hu a,b, Jian-Rong Li a,b, Mei-Ling Feng a, Xiao-Ying Huang a,⁎a State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, the Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR Chinab Graduate School of the Chinese Academy of Sciences, Beijing 100049, PR China

⁎ Corresponding author. Tel./fax: +86 591 83793727E-mail address: xyhuang@fjirsm.ac.cn (X.-Y. Huang)

1387-7003/$ – see front matter © 2010 Elsevier B.V. Aldoi:10.1016/j.inoche.2010.03.049

a b s t r a c t

a r t i c l e i n f o

Article history:Received 10 March 2010Accepted 31 March 2010Available online 7 April 2010

Keywords:AntimonyGermanateMicroporous materialCrystal structures

Two antimony germanates formulated as [(enH2)2.5][SbGe8O18(OH)4] (1) (en=ethylenediamine) andSb4Ge3O12 (2) have been solvothermally synthesized and structurally characterized. Compound 1 representsthe first organic containing microporous antimony germanate with three-dimensional (3D) channels.Compound 2 is isostructural to the scintillation crystal BGO (Bi4Ge3O12) with 3D inorganic compactstructure. The thermal stability of compound 1 and the optical properties of compound 2 have been studied.

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Microporous materials are of great importance because of theirwide range of applications in areas such as adsorption, separation, andcatalysis [1]. In addition to the most developed zeolites [2], zeolite-like microporous materials such as metal phosphates [3], metalphosphites [4], germanates [5,6], and metal–organic frameworks [7]have also been largely synthesized and investigated. Among them,open-framework germanates are of specific interest due to theirunique structural features [8]. For instance, germanium may adoptdifferent coordination geometries with oxygens ranging from tetra-hedron to octohedron. As a result, many well defined clusters such asGe7O17X2 and Ge9O22X4 (X=OH, F) as secondary building units(SBUs) have been found in germanates [6,9,10]. It is expected that theforming of such clusters are favorable for more open structures withlower framework density [11]. Normally, open-framework germa-nates are synthesized in the presence of organic amines as templates[9,12]. On the other hand, a strategy to further increase the structurediversity and to modify the properties of germanates is to incorporateother metal ions into the germanate frameworks. A number of metalions such as Be2+, B3+, Al3+, Zn2+, Ga3+ and Zr4+ have beensuccessfully incorporated into the germanates [13].

Sb(III) is interesting, for its active lone pair 5s2 electrons areinvisible structural directing agents and may lead to the distortion ofcoordinate configurations of antimony along with potential redoxsites, giving rise to unique properties in Sb(III)-based materials.Germanates incorporating antimony(III) are still rare. Several KTPtype inorganic structures with the general chemical formula of ASb(V)

OGeO4 (A=Na, K, Rb, Ag or Tl) have been synthesized via hightemperature solid state reactions [14]. In addition, two antimony(III)

germanates with compact structure, namely Sb2Ge3O9 [15] andSb4Ge3O12 [16] have been obtained. Herein, we report the firstopen-framework antimony germanate, namely, [(enH2)2.5][SbGe8O18

(OH)4] (1), and study the optical properties of Sb4Ge3O12 (2).A mixture of Sb2O3, GeO2 and pyrazine in ethylenediamine (en)

was heated at 433 K for 3 days. Colorless prismatic crystals of 1 wereobtained [17]. Single crystal X-ray diffraction [18] reveals thatcompound 1 crystallizes in space group Pbca (No. 61), and exhibitsan organically templated three-dimensional (3D) open-frameworkstructure with zeolite-like 3D channels running along the b axis, thecrystallographic [101] and [10-1] directions, respectively. The tem-plating double protonated ethylenediamine (enH2) cations lie in thechannels. As seen in Fig. S1, the crystallographically asymmetric unitof 1 contains half a crystallographically independent Sb3+ ion, fourunique Ge4+ ions, nine O2− ions, two OH− groups and one andquarter of double protonated enH2 cations. The Sb3+ ion is six-coordinated by six oxygen atoms to form one regular SbO6 octahedronwith Sb–O bond lengths ranging from 1.935 (8) to 1.945 (8) Å (TableS2). Both the Ge(1)4+ and Ge(2)4+ ions are coordinated by fouroxygen atoms to form GeO4 tetrahedra, respectively, whereas the Ge(3)4+ and Ge(4)4+ ions are five-coordinated by four oxygen atomsand one OH− group to form GeO5 trigonal bipyramids, respectively.Two groups of Ge–O bonds are found in each of the GeO5 trigonalbipyramids, three short equatorial bonds (1.750(10)–1.788(9) Å) andtwo long axial bonds (1.829(9)–2.023(8) Å). O(1)2− anions act astridentate metal linkers, O(10) and O(11) respectively form twoterminal hydroxyl groups, whereas the other O2− anions are allbidentate metal linkers.

Ge(1)O4 and Ge(2)O4 tetrahedra corner-share O(6) to form aGe2O7 unit, and Ge(3)O5 and Ge(4)O5 trigonal bipyramids are linkedby sharing O(8)–O(1) edge to form a Ge2O6(OH)2 unit. A Ge2O7 unit isfurther combined with a Ge2O6(OH)2 unit to form a [Ge4O11(OH)2]

Fig. 2. Polyhedral representation of the framework of 1 viewed along the b axis (a) andthe [101] direction (b).

790 B. Hu et al. / Inorganic Chemistry Communications 13 (2010) 789–792

tetranuclear unit by sharing two corners O(5) and O(7), in whichthere exist one Ge4O4 ring and one Ge2O2 ring, Fig. 1a. Then the Sb3+

ion connects two such Ge4O11(OH)2 tetranuclear units resulting in abody-centered parallelepiped [SbGe8O22(OH)4] heterometallic unit,Fig. 1b. Further, each [SbGe8O22(OH)4] heterometallic unit is linked toeight adjacent such units through sharing eight oxygen atoms togenerate a 3D anionic network of [SbGe8O18(OH)4]5− with the 3Dchannels. The protonated enH2 cations are disordered and they as thetemplates and charge balancing agents are located in the channels.Two kinds of channels are found in the 3D network, the channelsrunning along the b axis formed by sixteen-membered Ge8O8 rings,Fig. 2a, and the channels formed by twenty-membered Sb2Ge8O10

rings with terminal hydroxyl groups oriented toward the interiorfrom the view of the [101] and [10-1] directions, Fig. 2b. The crosssection of the channel is 3.0×2.8 Å along the b axis, and that of theother type of channel is 4.8×3.6 Å (measured by the O–O distancesacross the channels in each projection with a van der Waals radius of1.52 Å for oxygen subtracted). The solvent accessible volume is 45.2%(calculated by PLATON, excluding the enH2 cations).

The structure of compound 1 is closely related to that of therecently reported germanate open-framework materials [Ge9O22

(OH)4] [9,19–23], and with the similar cell parameters as that of thestructures reported by Yang [19] and Bensch [22]. Nevertheless, theincorporation of Sb3+ cations into anionic framework of [Ge9O18

(OH)4] by replacing the octohedral Ge4+ ions certainly not only leadsto a new composition of secondary building unit, but also alters thesize of unit cell, bond lengths of M–O(octohedra) and size of thechannels. Furthermore, it represents the first organic templatedgermanium–antimony oxide based microporous open-frameworkmaterial. Comparing to the compact structure of Sb2Ge3O9 [15] andSb4Ge3O12 [16], and alkali metal containing compounds [14], theethylenediamine molecules introduced in the synthesis may play animportant role in the formation of more open framework of 1.

Fig. 1. [Ge4O11(OH)2] tetranuclear unit (a) and [SbGe8O22(OH)4] heterometallic unit(b) in 1.

Thermogravimetric analysis (TGA) of compound 1 shows the totalweight loss of 22.4% till 983 K (Fig. 3). Calculated weight losses forcombustion of the organic templates plus loss of OH− (22.6%) are ingood agreement with the TGA experimental result. Its thermalstability agrees with that of the reported isostructural germanates[19,22].

Additionally, in the synthetic conditions similar to that forcompound 1, but with the absence of pyrazine, another antimonygermanate Sb4Ge3O12 (2) was synthesized. Using H2O as solventinstead of en, Sb4Ge3O12 crystals in good quality and with high yieldwere obtained. Compound 2 is isostructural to the scintillation crystal

Fig. 3. Thermogravimetric analysis (TGA) of compound 1.

Fig. 4. Optical absorption spectrum for compound 2, indicating the Eg of 3.51 eV.

791B. Hu et al. / Inorganic Chemistry Communications 13 (2010) 789–792

BGO (Bi4Ge3O12) [24] and BSO (Bi4Si3O12) [25] with 3D inorganiccompact structure. It's noteworthy that previously Sb4Ge3O12 wassynthesized hydrothermally at much higher temperature (720–820 K) [16]. Optical absorption spectrum for compound 2 (Fig. 4)indicates that the Eg of 2 is 3.51 eV, a little wider than that of the BGOcrystal (3.2 eV). In the emission spectrum of compound 2 (Fig. 5), thepeak at 492 nm may be assigned to the 3P1→1 S0 transition of theluminescent center Sb3+ [26].

In summary, the synthesis, crystal structure and selected proper-ties of two antimony germanates have been discussed. The successfulpreparation of the first organic templated microporous antimonygermanate [(enH2)2.5][SbGe8O18(OH)4], may open the possibility forsynthesizing other novel hybrid open-framework antimony germa-nates with new structural types. Compound Sb4Ge3O12 has been firstsynthesized under mild conditions.

Acknowledgements

Financial supports from the NNSF of China (Nos. 20771102 and20873149), NSF of Fujian Province (No. 2008J0174 ) and 973 Program(No. 2006CB932904) are greatly acknowledged.

Fig. 5. Emission spectrum of 2 of the solid state at room temperature (λex=207 nm).

Appendix A. Supplementary data

CCDC 765260 contains the supplementary crystallographic data forcompound 1. The data can be obtained free of charge via bhttp://www.ccdc.cam.ac.uk/conts/retrieving.htmlN, or from the Cambridge Crys-tallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:+44 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. CSD 421470contains the supplementary crystallographic data for compound 2. Thedata can be obtained by contacting the FIZ. Supplementary dataassociated with this article can be found, in the online version, atdoi:10.1016/j.inoche.2010.03.049.

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