A Ru(IV)O functional unit and an intercalating heteroligand, dipyridophenazine (dppz), are united in the complex cation of the title, 1, and responsible for its high DNA-cleavage activity and DNA affinity. In the solid state, the units of the RuOH2 analogue of 1 (ClO4-counterion) are linked by pi-stacking interactions similar to those in acridine orange and other conventional intercalators; the distance between the dppz ligands is 3.5 angstrom tpy = 2,2',2",-terpyridine.