Photochemistry of peroxo complexes induced by LMCT, MLCT and peroxide IL/LLCT excitation

Peroxide is a reductant as well as an oxidant. It follows that O22− as a ligand can serve as CT donor, but also as CT acceptor. In combination with oxidizing and reducing metals low-energy ligand-to-metal (LMCT) and metal-to-ligand (MLCT) transitions, respectively, occur. Photoredox reactions originating from such LMCT and MLCT excited states are well known. In the case of diperoxo complexes M(O2)2, peroxide intraligand transitions play an important role. IL excitation is followed by interligand charge transfer (LLCT) within the (O22−)2 moiety. As a result, a photodismutation to 2O2− and O2 takes place. Accordingly, IL excitation of MeReVII(O2)2O leads to the formation of MeReVIIO3 and O2.