Elsevier

Journal of Solid State Chemistry

Volume 258, February 2018, Pages 410-415
Journal of Solid State Chemistry

Synthesis and characterization of the first hydrothermally synthesized tin borate Sn2B3O6(OH)

https://doi.org/10.1016/j.jssc.2017.11.004Get rights and content

Abstract

In the system Sn-B-O-H, the first tin borate Sn2B3O6(OH) was successfully synthesized by a simple hydrothermal process. The compound crystallizes in the centrosymmetric monoclinic space group P21/n (no. 14) with the lattice parameters a = 443.5(2), b = 1102.5(4), c = 1396.4(5) pm, and β = 95.31(1)° (Z = 4). Structurally, Sn2B3O6(OH) features infinite chains of B3O8 groups connected along the a axis. The Sn2+ cations are arranged in form of layers between the anionic borate chains. Interestingly, Sn2B3O6(OH) is the first example of a hydrothermally synthesized tin borate, in which adjacent anionic borate chains are further connected by O–H···O hydrogen bond interactions into a three-dimensional structure. The characterization of Sn2B3O6(OH) is based on single-crystal X-ray diffraction data, vibrational spectroscopy, DFT calculations, and thermoanalytical investigations.

Graphical abstract

Synthesis and characterization of the first hydrothermally synthesized tin borate Sn2B3O6(OH).

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Introduction

Tin(II) compounds possess a wide range of potential applications including nanowires [1], rechargeable batteries [2], and solar cells [3]. Since the early 1990s, the search of new anode materials for high energy density applications is going on for lithium-ion batteries [4]. In this context, SnO has received a great deal of attention as a potential anode material due to its theoretically reversible specific capacity being much larger than that of graphite [5], [6]. In 1997, Idota et al. reported about a tin-based amorphous composite oxide (TCO) with the composition SnB0.56P0.40Al0.42O3.6 [7]. This tin-based amorphous oxide could replace the carbon-based lithium intercalation materials used as negative electrode of lithium-ion rechargeable batteries. Since the reasons have not yet been fully clarified and understood, several groups attempted to clarify the mechanisms on simplified variants of TCO glasses. For example, Holland et al. used the 11B and 119Sn nuclear magnetic resonance (NMR) spectroscopy to determine the local environment of boron and tin in binary tin borate glasses of the general composition xSnO(1-x)B2O3 (0.2 ≤ x ≤ 0.7) [8], [9]. In general, the boron atoms in these borate glasses possess the ability to coordinate to three or four oxygen atoms to form trigonal planar [BO3]3- or tetrahedral [BO4]5- groups. So far, several tin borate glasses have been reported including SnB2O4 (SnO-B2O3) [10], [11], [12] and Sn2B3O6.5 [13], which were synthesized under high-temperature conditions. Exploiting the possibility of pressure-induced-crystallization, the first crystalline tin borate β-SnB4O7 [9] was synthesized in our group in 2007 under high-pressure conditions of 7.5 GPa. Taking also quaternary phases into account, two crystalline phases with the composition CaSn1−xTix(BO3)2 [14] and Ni5SnB2O10 [15] are known.

Up to now, no crystalline tin borates have been synthesized in the system Sn-B-O-H under mild hydrothermal conditions. Based on our recent advances in hydrothermally synthesized compounds, we performed several experiments in this system, which led us to a new compound with the composition Sn2B3O6(OH). The hydrothermal synthesis, structure characterization through single-crystal X-ray diffraction, DFT calculations, and thermoanalytical investigations, as well as IR spectroscopy on the novel tin borate Sn2B3O6(OH) is presented in the following.

Section snippets

Synthesis

The compound Sn2B3O6(OH) was synthesized hydrothermally in a stainless-steel autoclave (volume: 8 mL) with a Teflon inlet. A mixture of SnO [161 mg, 1.2 mmol, Strem Chemicals, Inc. (≥99.8%, Newburyport, USA)], H3BO3 [131 mg, 2.4 mmol, Roth GmbH + Co. KG (≥99.8%, Karlsruhe, Germany)], H2O (0.5 mL), and a pH value adjusted to 14.0 by the addition of a few drops of a 2 M aqueous KOH was heated up to a temperature of 513 K and kept there for 2 days. Afterwards, the reaction mixture was cooled down with a

Results and discussion

The crystal structure of Sn2B3O6(OH) is built up from B3O8 groups forming infinite chains along the a axis (see Fig. 2). The Fundamental Building Block (FBB) consists of two corner-sharing BO4 tetrahedra and one BO3 triangle described as 2 [26] with the triangle and the square as pictograms for the trigonal-planar [BO3]3- and the tetrahedral [BO4]5- group, respectively. These two BO4 tetrahedra and one BO3 triangle are connected to form a B3O8 ring as shown in Fig. 2, encircled in red.

Conclusions

The first successful hydrothermal synthesis of the tin borate Sn2B3O6(OH) under mild conditions was reported. The structure is built up from B3O8 groups forming infinite chains and channels along the a axis where the Sn2+ cations are located inside these B3O8 channels. Sn2B3O6(OH) is the first compound in the system Sn-B-O-H.

Acknowledgment

We are very thankful to the Institute for Construction and Materials Science at the University of Innsbruck for granting us access to the devices for the thermoanalytical measurements.

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