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Borosulfates-Synthesis and Structural Chemistry of Silicate Analogue Compounds - PubMed

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Borosulfates-Synthesis and Structural Chemistry of Silicate Analogue Compounds

Jörn Bruns et al. Chemistry. 2020.

Abstract

Borosulfates are oxoanionic compounds consisting of condensed sulfur- and boron-centered tetrahedra. Hitherto, they were mostly achieved from solvothermal syntheses in SO3 -enriched sulfuric acid, or from reactions with the superacid H[B(HSO4 )4 ]. The crystal structures are very similar to those of the corresponding class of silicates and their substitution variants, especially regarding the typical structural motif of corner-sharing tetrahedra. However, the borosulfates are supposed to be even more versatile, because (BO3 ) units might also be part of the anionic network. The following article deals with detailed reports on the different synthesis strategies, the crystal chemistry of borosulfates in comparison to silicates, and their hitherto identified properties.

Keywords: boroselenates; borosulfates; crystal structure; inorganic synthesis.

© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1

Schematic description of hitherto obtained borosulfate structures including a classification in different dimensions. Red polyhedra represent the (BO4) units and yellow polyhedra the (SO4) units.

Figure 2
Figure 2

Non‐condensed complex anions [B(SO4)4]5− in K5[B(SO4)4] and [B(SO4)3(HSO4)]4− in K4[BS4O15(OH)] with an occupancy factor of 0.5 for the protons.

Figure 3
Figure 3

Protonated and non‐protonated borosulfate anions in Gd2[B2S6O24] (left) and Cu[B(SO4)2(HSO4)] (right).

Figure 4
Figure 4

Calculated free energy differences ΔG of the complex anion [B2(SO4)4(SO4H)2]4− between the hypothetical chair conformation (left) and the experimentally found twist conformation (right) as well as pK a values for the deprotonation to [B2(SO4)5(SO4H)]5− and to [B2(SO4)6]6−. Color code: blue—oxygen, yellow—sulfur, red—boron, and white—hydrogen.15

Figure 5
Figure 5

Cutout from the open‐branched chain 1∞ [B(SO4)4/2 ]− and the infinite loop‐branched chain 1∞ [B(SO4)2/2 (SO4)2/1 ]3−.

Figure 6
Figure 6

Extended unit cell of Li[B(SO4)2] in projection on (1 0 0).

Figure 7
Figure 7

TX 4 super‐tetrahedral units and the different observed connection modes for the known classical borosulfates.

Figure 8
Figure 8

The molecular anion [B(S2O7)2]− in the crystal structures of A[B(S2O7)2] (A=Li, Na, K, NH4).

Figure 9
Figure 9

Left: Extended unit cell with hydrogen bridging of H[B(SO4)(S2O7)] and anionic chains running parallel to the crystallographic c‐axis; right: Cut‐out of one anionic chain in H[B(SO4)(S2O7)], emphasizing the repeating {B(HSO4)2(S2O7)} units.

Figure 10
Figure 10

Extended unit cell of B2S2O9 in projection on (0 1 0), exhibiting (B2O7)‐centered double layers.

Figure 11
Figure 11

Left: View on top of an anionic layer of Cs2B2S3O13; right: (SO4) tetrahedra always pointing to the faces of the anionic layer in Cs2B2S3O13.

Figure 12
Figure 12

Left and right: Anionic chains with (B2O7) backbones in Ba[B2S3O13]/ Ba[B2O(SO4)3].

Figure 13
Figure 13

Left: molecular anion [B2O(SO4)6]8− in α‐Mg[B2O(SO4)6] and A[B2O(SO4)6] (A=Mn, Ni, Co, Zn); right: [B2S4O17]4− anion in Rb4B2S4O17.

Figure 14
Figure 14

Ternary plot of borosulfates charge compensated by monovalent cations. The classical borosulfates are all located on a line between A 2SO4 and the composition „B2O3⋅3SO3“. The unconventional borosulfates with S‐O‐S bridges are placed on a line between SO3 and ABS2O8 and the unconventional borosulfates with B‐O‐B bridges are found on a line between A 2SO4 and B2S2O9.

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