Metal-metal interactions in dinuclear (triphos)cobalt complexes exhibitingmixed valency

The spectroscopic and electrochemical properties of a series of dinuclear m ixed-valence complexes containing two (triphos)Co units are reported: [(tri phos)Co(L)Co(triphos)](+) (L = C6O4X2; X = H, Cl, Br, I, Me: 2a-e(+); L = C 14H4O4Me2: 4(+)). Complexes 2a-e(+) are bridged by tetraoxybenzene ligands and exhibit very strong metal-metal interaction leading to delocalized clas s-III behaviour while in 4(+) the extended tetraoxoanthracence bridging lig and leads to a partial electron localization. Additionally, the different o xidation behaviour of the parent dicationic complexes 1a-e(2+) and 3(2+) ha ve been investigated and are explained on the basis of a qualitative MO mod el.