Lewis basicity of the [Co 4 O 4 ] 4+ cubane core. Preparation of a mixed-valence (4Co II , 4Co III ) cluster with an unusual [Co 8 (µ 4 -O) 4 ] 2+ core, and new [Co 4 O 3 (OH)] 5+ and [Co 4 O 2 (OH) 2 ] 6+ cubane complexes

[Co8O4(O2CPh)12(MeCN)3(H2O)]1b is formed on oxidation of cobalt(II) benzoate in MeCN or dmf with aqueous H2O2, and contains a [Co4O4]4+ cubane unit with each oxide attached to an additional Co atom; studies stimulated by this result show that preformed [Co4O4(O2CR)2(bipy)4]2+(bipy = 2,2′-bipyridine) can be mono- and doubly-protonated to [Co4O3(OH)(O2CR)2(bipy)4]3+ and [Co4O2(OH)2(O2CR)2(bipy)4]4+, respectively.