ROLE OF METAL ATOM IN REVERSIBLE UPTAKE OF MOLECULAR OXYGEN . STRUCTURES OF MOLECULAR OXYGEN COMPLEXES FORMED BY BIS[BIS(DIPHENYLPHOSPHINO)ETHANE]IRIDIUM(I) HEXAFLUOROPHOSPHATE AND ITS RHODIUM ANALOG

The crystal and molecular structures of the molecular oxygen complexes of bis[bis(diphenylphosphino)ethane]iridium(I) hexafluorophosphate, [lr(O2){(C6H5)2PCH2CH2P(C6H5)2}2][PF6], and bis[bis(diphenyl-phosphino)ethane]rhodium(I) hexafluorophosphate, [Rh(O2){(C6H5)2PCH2CH2P(C6H5)2}2][PF6], have been determined from three-dimensional X-ray data. The two complexes are nearly isostructural, and the inner coordination around each metal atom is trigonal bipyramidal, considering the oxygen molecule as a monodentate ligand. The oxygen molecule is attached to the metal atom in the π-bonding fashion, with the two oxygen atoms equidistant from the metal. In the iridium complex, where addition of the oxygen is irreversible, the strong metal-to-oxygen bond is accompanied by a weak O-O bond, the O-O distance being 1.625 (23) Å, which is considerably longer than that expected for two oxygen atoms linked by a σ bond (1.49 Å). In the rhodium complex, where addition of oxygen isreversible, the weaker metal-to-oxygen bond results in a stronger O-O bond, the O-O distance being 1.418 (11) Å. Crystal data: the iridium complex crystallizes in space group P21/n, (C2h5), of the monoclinic system, with four molecules in a unit cell of dimensions a = 17.24 (3), b = 16.35 (3), c = 16.98 (3) Å, and β = 96.64 (2)°. The structure has been refined by least-squares techniques to a conventional R factor of 6.7% on F, using 2177 reflections, collected by counter methods, for which F2 > 2σ(F2). No crystallographic symmetry is imposed upon the discrete, monomeric ions. The Ir-P distances vary noticeably from 2.283 (7) to 2.452 (9) Å. The equivalent data for the analogous rhodium complex, prepared here for the first time, are a = 17.18 (2), b = 16.49 (2), c = 16.96 (2) Å, β = 95.20 (3)°, Z = 4, and space group P21/n. The least-squares refinement on F, using 2048 independent reflections, collected by counter methods, for which F2 > 3σ(F2), converged to a conventional R factor of 5.2%. The Rh-P distances vary from 2.336 (4) to 2.362 (4) Å. © 1969, American Chemical Society. All rights reserved.