The High-pressure Thallium Triborate HP-TlB3O5 Gerhard Sohra, Lukas Perflerb and Hubert Huppertza a Institut für Allgemeine, Anorganische und Theoretische Chemie, Leopold-Franzens- Universität Innsbruck, Innrain 80 – 82, A-6020 Innsbruck, Austria b Institut für Mineralogie und Petrographie, Leopold-Franzens-Universität Innsbruck, Innrain 52f, A-6020 Innsbruck, Austria Reprint requests to H. Huppertz. E-mail: [email protected] Z. Naturforsch. 2014, 69b, 1260 – 1268 / DOI: 10.5560/ZNB.2014-4124 Received June 2, 2014 Dedicated to Professor Hubert Schmidbaur on the occasion of his 80th birthday The thallium triborate HP-TlB3O5 (HP = high-pressure) was synthesized in a Walker-type multi- anvil apparatus under high-pressure=high-temperature conditions of 6 GPa and 1400◦C. A mixture of ◦ thallium carbonate Tl2CO3 and boric acid H3BO3 initially heated at 850 C under ambient-pressure conditions was used as a precursor for the high-pressure experiment. Single-crystal X-ray diffrac- 0 0 tion data revealed that HP-TlB3O5 is isotypic to HP-M B3O5 (M = K, Rb). Furthermore the B–O 00 00 network is identical to the substitutional variants HP-M B3O5 [M = Cs1−x(H3O)x (x = 0.5 – 0.7), NH4]. HP-TlB3O5 crystallizes with eight formula units (Z = 8) in the monoclinic space group C2=c (no. 15). The lattice parameters are a = 996.3(2), b = 884.0(2), c = 913.1(2) pm, b = 103:3(1)◦, and 3 V = 782.5(3) Å . Trigonal-planar BO3 groups, corner-sharing BO4 tetrahedra, and B2O6 groups con- sisting of two edge-sharing BO4 tetrahedra are present in the structure, forming a three-dimensional network. The thallium ions are located in channels of the boron-oxygen network being tenfold coor- dinated by oxygen atoms and do not show any lone pair effect at all. IR and Raman spectroscopic investigations were performed on single crystals of the compound. Key words: High-pressure, Borate, Crystal Structure, Lone Pair, Thallium Introduction the first borate containing oxonium ions [17]. This finding proves that alkali metal cations can be sub- + Since the publication of KZnB3O6 [1–3], we fo- stituted by pseudo alkali metal ions like H3O in cused our research on the syntheses of high-pressure high-pressure borates. With the substitutional vari- alkali metal borates. KZnB3O6 was the first ex- ant HP-(NH4)B3O5, we recently synthesized a high- ample of two borates synthesized under ambient- pressure borate containing solely the pseudo alkali + pressure conditions exhibiting the structural motive metal cation NH4 [18]. Another pseudo alkali metal of edge-sharing BO4 tetrahedra [3,4]. At that time, cation is thallium(I). In contrast to the above men- all other compounds containing edge-sharing BO4 tioned alkali and pseudo alkali metal cations, it has tetrahedra were high-pressure phases, e. g. RE4B6O15, two valence electrons left forming a lone pair. De- + (RE = Dy, Ho) [5], a-RE2B4O9 (RE = Sm, Eu, Gd, pending on the surrounding of the Tl ion, this lone Tb, Ho) [6,7], HP- MB2O4 (M = Ni, Co) [8,9], b- pair can either be stereochemically active or inac- FeB2O4 [10], and Co7B24O42(OH2) · 2 H2O[11]. In- tive [19]. terestingly, any high-pressure alkali metal borates Up to now, eleven phases are known in the sys- were known to literature. Since then, we success- tem Tl-B-O, but only five of them have been exam- fully synthesized high-pressure borates of all alkali ined structurally. One of them, TlB5O8, is the only one metal cations represented by the compounds HP- without a lone pair effect [20]. The normal-pressure LiB3O5 [12], HP-Na2B4O7 [13], HP-MB3O5 (M = K, compound TlB3O5 is built up from B3O3 rings which Rb) [14, 15], and HP-CsB5O8 [16]. During the sys- are linked to each other by bridging oxygen atoms to tematic scanning of the system Cs-B-O, we discov- form a three-dimensional framework. A small lone pair ered HP-Cs1−x(H3O)xB3O5 (x = 0.5 – 0.7) which is effect is observed in its stucture [21]. In contrast, b- © 2014 Verlag der Zeitschrift für Naturforschung, Tübingen · http://znaturforsch.com G. Sohr et al. · High-pressure Thallium Triborate HP-TlB3O5 1261 Tl2B4O7, TlBO2 and Tl3BO3 show a remarkably stere- Experimental Section ochemically active lone pair [19, 22, 23]. The com- pounds a- and g-Tl2B4O7 [24, 25] have been charac- Synthesis terized by powder diffraction only, as well as Tl2B8O13 and the high-pressure phase TlBO3 [21, 26]. Further- HP-TlB3O5 was synthesized in two steps during a sys- tematic scan of the system Tl-B-O. First, an ambient- more, TlB9O14 and Tl4B2O5 are stated, but no crystal- lographic proof is given [25, 27]. pressure=high-temperature synthesis was carried out. A stoi- This work presents the new thallium triborate HP- chiometric educt mixture of 0:7400 g (1:5786 mmol) Tl2CO3 TlB O . The compound was synthesized under high- (99:995%, Alfa Aesar, Karlsruhe, Germany) and 0:5857 g 3 5 (9:4723 mmol) H BO (99:5%, Carl Roth, Karlsruhe, Ger- pressure conditions and characterized by powder and 3 3 many) was ground together in an agate mortar and filled single-crystal X-ray diffraction as well as by IR into an FKS 95=5 (Feinkornstabilisiert, 95% Pt, 5% Au) and Raman spectroscopy. Its structure and the vibra- crucible (no. 21, Ögussa, Vienna, Austria). The mixture was tional spectra are discussed in comparison with the heated to 600◦C in 6 h and kept at this temperature for 4 h. 0 0 isotypic phases HP-M B3O5 (M = K, Rb) and the Further heating up to 850◦C lasted 3 h. After holding the 00 00 substitution variants HP-M B3O5 [M = Cs1−x(H3O)x temperature for 36 h, the mixture was quenched to room (x = 0.5 – 0.7), NH4]. Furthermore, the effect of the temperature. The resulting product was finely ground, filled lone pair is examined. into a crucible made of hexagonal boron nitride (HeBoSint® Empirical formula HP-TlB3O5 Table 1. Crystal data and Molar mass, g mol−1 316.80 structure refinement of HP- Crystal system monoclinic TlB3O5 (standard devia- Space group C2=c (no. 15) tions in parentheses). Powder diffractometer Stoe Stadi P Radiation; wavelength, pm MoKa1; l = 70.930 Powder data a, pm 996.26(6) b, pm 883.91(6) c, pm 913.01(6) b, deg 103.30(1) V, Å3 782.4(1) Single-crystal diffractometer Enraf-Nonius Kappa CCD Radiation; wavelength, pm MoKa ; l = 71.073 Single-crystal data a, pm 996.3(2) b, pm 884.0(2) c, pm 913.1(2) b, deg 103.3(1) V, Å3 782.5(3) Formula units per cell, Z 8 Calculated density, g cm−3 5.38 F(000), e 1088 Crystal size, mm3 0.07 × 0.06 × 0.02 Temperature, K 293(2) Absorption coefficient, mm−1 41.2 q range, deg 3.1 – 37.8 Range in hkl −17 ≤ h ≤ 16, −15 ≤ k ≤ 15, −15 ≤ l ≤ 15 Total no. of reflections 7287 Absorption correction multi-scan [33] Independent reflections = Rint = Rs 2093 = 0.0893 = 0.0709 Reflections with I > 2 s(I) 1376 Data=refined parameters 2093 = 83 2 Goodness-of-fit on Fi 1.042 Final R1 = wR2 [I > 2 s(I)] 0.0477 = 0.0818 R1 = wR2 (all data) 0.0477 = 0.0818 Largest diff. peak=hole, e Å−3 2.66 = −4.52 1262 G. Sohr et al. · High-pressure Thallium Triborate HP-TlB3O5 0 0 P100, Henze BNP GmbH, Kempten, Germany), and com- ters being comparable to those of HP-M B3O5 (M = K, Rb) 00 00 pressed by eight tungsten carbide cubes (HA-7%Co, Hawe- and HP-M B3O5 (M = Cs1−x(H3O)x (x = 0.5 – 0.7), NH4), dia, Marklkofen, Germany) via an 18=11-assembly. A hy- the positional parameters of HP-KB3O5 were used as start- draulic press (mavo press LPR 1000-400=50, Max Voggen- ing values for the refinement of the structure in the mono- reiter GmbH, Mainleus, Germany) and a Walker-type mod- clinic space group C2=c, since the two phases are isotypic. ule (also Max Voggenreiter GmbH) were used to apply the All atoms were refined with anisotropic displacement para- pressure. The assembly and its preparation are described in meters, and the final difference Fourier syntheses did not re- the references [28– 31]. The compression of the precursor to 6 GPa lasted 3 h. At this pressure, the sample was heated to 1400◦C within 10 min and kept there for 10 min. After cool- ing to 800◦C within 5 h, the heating was turned off to quench the reaction mixture to room temperature. The decompres- sion of the assembly lasted 9 h. The sample was separated from the surrounding octahe- dral pressure medium (MgO, Ceramic Substrates & Compo- nents Ltd., Newport, Isle of Wight, UK) and removed from the boron nitride crucible. The sample consisted of color- less crystals, which were found to be HP-TlB3O5. Under air, brown dots formed on the surface of the crystals. Crystal structure analysis To measure the powder X-ray diffraction pattern of HP- TlB3O5, a Stoe Stadi P powder diffractometer with Ge(111)- Fig. 1. Experimental powder pattern of HP-TlB3O5 (top), monochromatized MoKa1 radiation (l = 70:93 pm) was compared with the theoretical powder pattern (bottom) simu- used in transmission geometry. Fig.1 shows the experimen- lated from single-crystal data. The reflection marked with an asterisk is caused by hexagonal boron nitride of the crucible. tal powder pattern of HP-TlB3O5 matching well with the theoretical pattern simulated from the single-crystal data.