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
(SO4)4sup>5- there is no condensation, each ion stands alone. In
(SO4)3sup>3- the anions are linked into a chain, a chain of loops, or as
2(SO4)6sup>6− in a cycle. Finally in
(SO4)2sup>− 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
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...
. The first borosulfate to be discovered was K
5 (SO4)4in 2012.
Over 75 unique compounds are known.
They are distinct from the
borate sulfate
Borate sulfates are mixed anion compounds containing separate borate and sulfate anions. They are distinct from the borosulfates The borosulfates are heteropoly anion compounds which have sulfate groups attached to boron atoms. Other possible ter ...
s which have separate, uncondensed sulfate and borate ions.
Related compounds include
boroselenates The boroselenates are chemical compounds containing interlinked borate and selenate groups sharing oxygen atoms. Both selenate and borate groups are tetrahedral in shape. They have similar structures to borosulfates and borophosphates The borophosp ...
,
borotellurates The borotellurates are heteropoly anion compounds which have tellurate groups attached to boron atoms. The ratio of tellurate to borate reflects the degree of condensation. In eO4(BO3)2sup>8- the anions are linked into a chain. In eO2(BO3)4sup>10â ...
,
and also
boroantimonates,
borogallates,
borogermanates,
borophosphates The borophosphates are mixed anion compounds containing borate and phosphate anions, which may be joined together by a common oxygen atom. Compounds that contain water or hydroxy groups can also be included in the class of compounds.
Borophosphates ...
,
boroselenites The boroselenites are heteropoly anion chemical compounds containing selenite and borate groups linked by common oxygen atoms. They are not to be confused with the boroselenates with have a higher oxidation state for selenium, and extra oxygen
...
and
borosilicates.
Formation
Borosulfates are formed by heating
boric oxide
Boron trioxide or diboron trioxide is the oxide of boron with the formula . It is a colorless transparent solid, almost always glassy (amorphous), which can be crystallized only with great difficulty. It is also called boric oxide or boria. It h ...
,
oleum
Oleum (Latin ''oleum'', meaning oil), or fuming sulfuric acid, is a term referring to solutions of various compositions of sulfur trioxide in sulfuric acid, or sometimes more specifically to disulfuric acid (also known as pyrosulfuric acid). Ole ...
, or
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
, with metal carbonates. The degree of condensation is varied with the ratio of oleum to sulfuric acid. Pure oleum is more likely to yield compounds with
disulfate
In chemistry, disulfate or pyrosulfate is the anion with the molecular formula . Disulfate is the IUPAC name.
It has a dichromate-like structure and can be visualised as two corner-sharing SO4 tetrahedra, with a bridging oxygen atom.
In this a ...
groups.
Reactions
When heated to around 500 °C the borosulfates decompose by emitting SO
3 vapour and form a metal sulfate and boric oxide.
List
References
{{Borates
Borates
Sulfates