Appearance purple solid | ||
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Potassium osmate is the inorganic compound with the formula K2[OsO2(OH)4]. It contains Osmium in the VI (6+) oxidation state. It is a diamagnetic purple salt that gained attention as a catalyst for the asymmetric dihydroxylation of olefins. When dissolved in water a pink solution is formed. But when dissolved in methanol the solution is blue.
Like related d2 complexes, the oxo ligands are trans. The Os=O and Os-OH distances are 1.75(2) and 1.99(2) Å, respectively. It is a relatively rare example of a metal oxo complex that obeys the 18e rule. The compound was first reported by Edmond Frémy in 1844.
Osmate salts can be produced by reducing perosmates using alcohol. Osmium tetroxide is dissolved in potassium hydroxide water solution to produce K2[OsO4(OH)2], which is then reduced to potassium osmate. Another way to make this is by alkaline oxidative fusion of osmium metal.