Percobaltate
{{Short description|Chemical compounds}}
Percobaltates are chemical compounds where the oxidation state of cobalt is +5. This is the highest established oxidation state of cobalt.{{cite journal|last1=Riedel|first1=Sebastian|last2=Kaupp|first2=Martin|title=The highest oxidation states of the transition metal elements|journal=Coordination Chemistry Reviews|date=March 2009|volume=253|issue=5–6|pages=606–624|doi=10.1016/j.ccr.2008.07.014}} The simplest of these are bi-metallic Group 1 oxides such as sodium percobaltate (Na3CoO4); which may be produced by the reaction of cobalt(II,III) oxide and sodium oxide, using oxygen as the oxidant:
: 4 Co3O4 + 18 Na2O + 7 O2 → 12 Na3CoO4
The potassium salt can be synthesized similarly; its magnetic moment has indicated the existence of cobalt(V).{{cite journal|last1=Brendel|first1=Claus|last2=Klemm|first2=Wilhelm|title=Weitere Versuche zur Darstellung von Kaliumcobaltat (V)|journal=Zeitschrift für anorganische und allgemeine Chemie|date=January 1963|volume=320|issue=1–4|pages=59–63|doi=10.1002/zaac.19633200109|language=German}}{{cite book|author=D. Nicholls|title=The Chemistry of Iron, Cobalt and Nickel: Comprehensive Inorganic Chemistry|url=https://books.google.com/books?id=pD79BAAAQBAJ&pg=PA1107|date=2 October 2013|publisher=Elsevier Science|isbn=978-1-4831-4643-0|pages=1107–}} No crystallographic analysis has been reported for either material. Percobaltates can be stabilized by use of oxides or fluorides.{{cn|date=February 2017}}
A number of organometallic Co(V) complexes have also been reported.