Crystalline borosulfates are a young but ever expanding class of silicate-analogous materials with the first representative K5[B(SO4)4] published in 2012 and over 60 characterized compounds by the end of 2020. They may be classified silicate-analogous in two ways: Firstly, the anionic substructure consists exclusively of borate and sulfate tetrahedra. Secondly, the boron atoms may be treated as coordinated by sulfate tetrahedra yielding supertetrahedra TX4 as B(SO4)4. Using these supertetrahedra they can be classified as e. g. band, layer and tectosilicate-analogous. Recently, we reported the second tectosilicate-analogous borosulfate Bi(H3O)[B(SO4)2]4 comprising corner sharing supertetrahedra, only. Consequently, channels of Vierer and Achter rings are formed by the supertetrahedra. In the former, the Bi3+ cation is localized and in the latter the H3O+. Bi(H3O)[B(SO4)2]4 is the first borosulfate comprising two differently charged cations. New results show that the borosulfates Bi(NO2)[B(SO4)2]4 and Bi(NH4)[B(SO4)2]4 crystallize homeotypic to Bi(H3O)[B(SO4)2]4. The choice of cation H3O+, NO2+ or NH4+ located inside the supertetrahedra Achter rings can be controlled by solvothermal synthesis and is accompanied by slight changes of the unit cell, only. The presence of the respective cation can be confirmed by IR spectroscopy and careful analysis of the powder X-ray diffractograms. All three borosulfates show non-linear optical properties (SHG, second harmonic generation). Especially Bi(NH4)[B(SO4)2]4 could be a promising material for proton transport since high proton conductivity is reported for another ammonium borosulfate, namely NH4[B(SO4)2].

Tectosilicate-analogous and SHG-active borosulfates Bi(H3O)[B(SO4)2]4, Bi(NO2)[B(SO4)2]4, and Bi(NH4)[B(SO4)2]4

ACS Spring Meeting 2021

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