Reversible solid-state interconversion of rhodizonic acid H2C6O6 into H6C6O8 and the solid-state structure of the rhodizonate dianion C6O62- (aromatic or non-aromatic?)

Anhydrous rhodizonic acid H2C6O6 is obtained by (fully reversible) thermal dehydration of solid 2,3,5,5,6,6-hexahydroxycyclohex-2-ene 1,4-dione, H6C6O 8, commonly known as rhodizonic acid dihydrate. Treatment of H6C6O8 with Rb OH yields crystals of Rb2C6O6; the oxocarbon dianion C6O62- is shown to pos sess a flat, benzene-type structure, with C-C bonds shorter than expected f or a (non-aromatic) ketonic-type structure.