Percobaltates are chemical compounds where the oxidation state of cobalt is +5. This is the highest established oxidation state of cobalt. The simplest of these are bi-metallic Group 1 oxides such as sodium percobaltate (Na<sub>3</sub>CoO<sub>4</sub>); which may be produced by the reaction of cobalt(II,III) oxide and sodium oxide, using oxygen as the oxidant:
The potassium salt can be synthesized similarly; its magnetic moment has indicated the existence of cobalt(V). No crystallographic analysis has been reported for either material. Percobaltates can be stabilized by use of oxides or fluorides.
A number of organometallic Co(V) complexes have also been reported.