Rubidium metaborate, Rb3B3O6, was obtained by the reaction of Rb2CO3 and BN using a radiofrequency furnace at a maximum reaction temperature of 1173 K. The crystal structure has been determined by single-crystal X-ray diffraction. The space group is , with all atoms positioned on a twofold axis (Wyckoff site 18e). The ionic compound is isotypic with Na3B3O6, K3B3O6 and Cs3B3O6

Schmid, Sabine

Schnick, Wolfgang

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Rubidium metaborate, Rb3B3O6Sabine Schmid and Wolfgang Schnick*Department Chemie und Biochemie, Lehrstuhl fuÈ r Anorganische FestkoÈ rperchemie,Ludwig-Maximilians-UniversitaÈt, Butenandtstraûe 5-13 (D), D-81377 MuÈnchen,GermanyCorrespondence e-mail: wolfgang.schnick@uni-muenchen.deReceived 15 April 2004Accepted 26 April 2004Online 30 June 2004Rubidium metaborate, Rb3B3O6, was obtained by the reactionof Rb2CO3 and BN using a radiofrequency furnace at amaximum reaction temperature of 1173 K. The crystalstructure has been determined by single-crystal X-raydiffraction. The space group is R3c, with all atoms positionedon a twofold axis (Wyckoff site 18e). The ionic compound isisotypic with Na3B3O6, K3B3O6 and Cs3B3O6.CommentA wide variety of alkali borates have been reported. The titlecompound, Rb3B3O6, belongs to the series of alkali meta-borates M3B3O6 (M = Li, Na, K, Rb and Cs). Surprisingly, asingle-crystal structure determination of Rb3B3O6 has notbeen published previously; Schneider & Carpenter (1970) andSchlaeger & Hoppe (1994) assumed Rb3B3O6 to be isotypicwith the other alkali metaborates, but the structure has neverbeen examined by single-crystal X-ray diffraction. We presenthere the crystal structure of Rb3B3O6, solved and re®ned fromX-ray diffraction data.We con®rm that Rb3B3O6 is isotypic with Na3B3O6(Marezio et al., 1963), K3B3O6 (Schneider & Carpenter, 1970)and Cs3B3O6 (Schlaeger & Hoppe, 1994).The lattice parameters increase from Na to Cs, along withthe size of the cations. The previously published lattice para-meters of Rb3B3O6 (Schneider & Carpenter, 1970) are nearlyequivalent to those found in the present investigation. Thecharacteristic building units are cyclic planar B3O63ÿ anions,which can be described as comprising three corner-sharingBO33ÿ groups. The BÐO bond length for terminal atom O1 is1.315 (6) AÊ , while the BÐO bond to bridging atom O2[1.407 (3) AÊ ] is signi®cantly longer. The BÐO distancesof the M3B3O6 (M = Na, K, Rb and Cs) series are comparedin Table 1. The B3O63ÿ rings in Rb3B3O6 are stacked in astaggered manner along [001], with consecutive rings rotatedwith respect to one another by 60 (Figs. 1 and 2). Each Rbatom is surrounded by seven O atoms, with RbÐO distancesof 3 AÊ .ExperimentalRb3B3O6 was obtained by the high-temperature reaction of Rb2CO3(2.0 mmol) and BN (2.0 mmol) using a radiofrequency (rf) furnace.Details of the experimental set-up are given in Schnick et al. (1999).Under an atmosphere of pure argon, the starting compounds wereplaced in a tungsten crucible, which was positioned at the center ofthe induction coil of an rf furnace. The reaction was performed underan atmosphere of pure nitrogen (puri®ed by silica gel, potassiumhydroxide, molecular sieve, P4O10 and a BTS catalyst). The reactionbatch was heated to 1173 K at a rate of 7.3 K minÿ1. The temperaturewas maintained for 2 h and then the product was cooled at a rate of0.2 K minÿ1 to 473 K. Subsequently, the mixture was quenched toroom temperature. Rb3B3O6 was obtained as a coarse crystallinewhite solid mixed with RbCN.Acta Cryst. (2004). C60, i69±i70 DOI: 10.1107/S0108270104010066 # 2004 International Union of Crystallography i69inorganic compoundsActa Crystallographica Section CCrystal StructureCommunicationsISSN 0108-2701Figure 1The crystal structure of Rb3B3O6, viewed along the crystallographic caxis, with 99% probability displacement ellipsoids.Figure 2The Rb atom surrounded by B3O63ÿ rings, with 99% probability dis-placement ellipsoids.inorganic compoundsi70 Schmid and Schnick  Rb3B3O6 Acta Cryst. (2004). C60, i69±i70Crystal dataRb3B3O6Mr = 384.85Trigonal, R3ca = 13.1572 (19) AÊc = 7.7434 (15) AÊV = 1160.9 (3) AÊ 3Z = 6Dx = 3.303 Mg mÿ3Mo K radiationCell parameters from 8606re¯ections = 3.1±40.3 = 18.87 mmÿ1T = 293 (2) KBlock, colourless0.38  0.19  0.17 mmData collectionNonius KappaCCD diffractometer’ and ! scansAbsorption correction: numerical(X-SHAPE; Stoe & Cie, 1999),Tmin = 0.056, Tmax = 0.1545001 measured re¯ections231 independent re¯ections226 re¯ections with I > 2(I )Rint = 0.082max = 25h = ÿ15! 15k = ÿ15! 15l = ÿ9! 9Re®nementRe®nement on F 2R(F ) = 0.019wR(F 2) = 0.046S = 1.22231 re¯ections22 parametersw = 1/[2(F 2o) + (0.0139P)2+ 8.1199P]where P = (F 2o + 2F2c )/3(/)max < 0.001max = 0.43 e AÊÿ3min = ÿ0.40 e AÊ ÿ3Extinction correction: SHELXL97Extinction coef®cient: 0.00105 (19)Data collection: COLLECT (Nonius, 1997±2000); cell re®nement:HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction:HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK;program(s) used to solve structure: SHELXS97 (Sheldrick, 1997);program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997);molecular graphics: DIAMOND (Brandenburg, 1999); software usedto prepare material for publication: PLATON (Spek, 2003) andWinGX (Farrugia, 2003).This work was supported by the Fonds der ChemischenIndustrie, Germany, and by the Deutsche Forschungsge-meinschaft.Supplementary data for this paper are available from the IUCr electronicarchives (Reference: IZ1042). Services for accessing these data aredescribed at the back of the journal.ReferencesBrandenburg, K. (1999). DIAMOND. Release 2.1c. Crystal Impact GbR,Bonn, Germany.Farrugia, L. J. (2003). WinGX. Version 1.64.05. University of Glasgow,Scotland.Marezio, M., Plettinger, H. A. & Zachariasen, W. H. (1963). Acta Cryst. 16,594±595.Nonius (1997±2000). COLLECT. Nonius BV, Delft, The Netherlands.Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276,Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M.Sweet, pp. 307±326. New York: Academic Press.Schlaeger, M. & Hoppe, R. (1994). Z. Anorg. Allg. Chem. 620, 1867±1871.Schneider, W. & Carpenter, G. B. (1970). Acta Cryst. B26, 1189±1191.Schnick, W., Huppertz, H. & Lauterbach, R. (1999). J. Mater. Chem. 9, 289±296.Sheldrick, G. M. (1997). SHELXL97 and SHELXS97. Release 97±2.University of GoÈ ttingen, Germany.Spek, A. L. (2003). PLATON. Utrecht University, The Netherlands.Stoe & Cie (1999). X-SHAPE. Version 1.06. Stoe & Cie, Darmstadt, Germany.Table 1A comparison of BÐO distances (AÊ ) and OÐBÐO angles () inNa3B3O6, K3B3O6, Rb3B3O6 and Cs3B3O6.Compound BÐO1 BÐO2 O2ÐBÐO2 O2ÐBÐO1Na3B3O6 1.28 (2) 1.43 (1) 114.5 (6) 122.8 (7)K3B3O6 1.33 (1) 1.398 (5) 117.3 (8) 121.3 (4)Rb3B3O6 1.315 (6) 1.407 (3) 115.7 (5) 122.1 (2)Cs3B3O6 1.298 (8) 1.416 (4) 114.8 (3) 122.6 (3)

Rubidium metaborate, Rb3B3O6

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