Synthesis, Characterization, and Crystal Structure of a New Trisodium Triborate, Na 3 [B 3 O 4 (OH) 4 ]

Abstract : The preparation of a new trisodium triborate, Na 3 [B 3 O 4 (OH) 4 ], and its complete characterization in terms of molecular structure and thermal behaviour are reported. Synthesis of this compound was achieved by thermal treatment of Na[B(OH) 4 ]·2H 2 O or NaBH 4 hydrolysis. The crystal structure was determined by single-crystal X-Ray diffraction. The trisodium triborate crystallized in the monoclinic system (a = 12.8264(6) Å, b = 7.7276(4) Å, c = 6.9690(3) Å and β = 98.161(3) °), space group C c, Z = 2. The structure of Na3[B3O4(OH)4] comprised [B3O4(OH)4]3- polyanions, based on B-O containing rings with two tetra-coordinated boron atoms and one tri-coordinated boron atom in the fragments BO2(OH)2 and BO3, respectively. These polyanions are interconnected by four intermolecular hydrogen bonds and presented a tilt of 10.470(4)Å compared to the a axis. Thus, they are stacked by rotation of about 180° around an axis defined by the three-coordinated boron atoms and parallel to the c axis. Such polyanions were only observed previously in two synthetic compounds, M3[B3O4(OH)4]·2H2O with M = K and Rb, which were isostructural. The originality of the present work was the synthesis and the description of a different crystallographic structure containing this polyanion. Characteristic peaks ranging from 500 to 1500 cm-1 and around 3300 cm-1 highlighted the presence of the B-O rings and hydroxyl groups, respectively. The decomposition temperature T= 155 °C was obtained by ThermoGravimetric Analysis and the following equivalent formula in terms of hydration degree was proposed: NaBO2·2/3H2O. Na3[B3O4(OH)4] decomposed into Na3[B3O5(OH)2] in equilibrium with its vapour.
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Inorganic Chemistry, American Chemical Society, 2010, 49 (11), pp.4830 - 4835. 〈10.1021/ic902525s〉
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Jérôme Andrieux, Christelle Goutaudier, Laetitia Laversenne, Erwann Jeanneau, Philippe Miele. Synthesis, Characterization, and Crystal Structure of a New Trisodium Triborate, Na 3 [B 3 O 4 (OH) 4 ]. Inorganic Chemistry, American Chemical Society, 2010, 49 (11), pp.4830 - 4835. 〈10.1021/ic902525s〉. 〈hal-01611575〉

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