The crystal structures of the PF₆ and ClO₄ salts of [IrO₂(dppm)₂][dppm = bis(diphenylphosphino)methane] have been determined by X-ray diffraction methods from counter data. Crystals of both compounds are monoclinic, space group P2₁/c, with Z= 4. [PF₆]^– salt (I) : a= 11.40(1), b= 19.26(1). c= 22.06(4)Å, β= 101.2(1)°. [ClO₄]^– salt (II) : a= 11.87(1), b= 11.12(1), c= 34.6(3)Å, β= 96.1 (1)°. The structures have been solved by the heavy-atom method and refined by least squares to R 0.06 for ca. 3 400 observed reflections in both cases. The O–O distances [1.45(2)(I) and 1.49 (1)Å(II)] are identical within the precisionofthe analyses. Although the packing in the two compounds differs greatly, the geometry of the cation remains the same in each and is trigonal bipyramidal, with the dioxygen ligand occupying one equatorial site. The cation is chiral and mean bond lengths and angles are: Ir–P(ax) 2.36. Ir–P(eq) 2.31, Ir–O 2.02, O–O 1.47 Å: P(ax)-Ir-P(ax) 170, P(ax)–Ir–P(eq) 70°(within the chelate ring).