Osmiates

Osmiates are a class of chemical compounds containing the osmate anion. The osmate anion is a polyatomic ion with the general formula [OsOx]n-, where Os is osmium and O is oxygen. The most common and stable osmate anion is the tetraoxoosmate(VI) ion, [OsO4]2-, which is a derivative of osmium tetroxide (OsO4). Osmium tetroxide itself is a neutral molecule, but in alkaline solutions, it can form the tetraoxoosmate(VI) anion. Other osmate anions with different oxidation states of osmium are also known, but they are generally less stable or less common.

The tetraoxoosmate(VI) ion typically exists in aqueous solutions, particularly under alkaline conditions. It is a diamagnetic species and has a tetrahedral geometry around the osmium atom. The color of osmate solutions can vary depending on the specific ion and its concentration, often appearing yellow or orange. Osmium tetroxide is a volatile, corrosive, and toxic substance, and its reactions to form osmates are carried out with caution.

Osmium compounds, including osmates, are rarely found in nature and are primarily synthesized in laboratories. They are often used as oxidizing agents in organic chemistry. For example, osmium tetroxide in the presence of a co-oxidant is used for the dihydroxylation of alkenes, a reaction that forms vicinal diols. The osmate anion can be formed during these catalytic cycles. Research into the properties and applications of osmium compounds, including osmates, continues to be an area of interest in inorganic and organic chemistry.