Abstract A tetranuclear mixed-valence manganese(II,III) complex, [Mn2(O)(Ph2MeCCOO)2(phen)2]2(PF6)2·10H2O (2), has been assembled from a binuclear manganese(II) complex, [Mn(Ph2MeCCOO)(phen)2]2(PF6)2·2MeCN (1) by use of a photo-induced oxidation reaction.