The borosulfates are heteropoly anion compounds which have sulfate groups attached to boron atoms. Other possible terms are sulfatoborates or boron-sulfur oxides. The ratio of sulfate to borate reflects the degree of condensation. With [B(SO4)4]5- there is no condensation, each ion stands alone. In [B(SO4)3]3- the anions are linked into a chain, a chain of loops, or as [B2(SO4)6]6− in a cycle. Finally in [B(SO4)2]− the sulfate and borate tetrahedra are all linked into a two or three-dimensional network. These arrangements of oxygen around boron and sulfur can have forms resembling silicates. The first borosulfate to be discovered was K5[B(SO4)4] in 2012 by the research group of Henning Höppe,[1][2] although the compound class as such had been postulated already in 1962 by G. Schott and H. U. Kibbel.[3] Over 80 unique compounds are known as of 2024.
They are distinct from the borate sulfates which have separate, uncondensed sulfate and borate ions.
Related compounds include boroselenates, borotellurates,[4] and also boroantimonates, borogallates, borogermanates, borophosphates, boroselenites and borosilicates.[5]
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