CRYSTAL AND MOLECULAR-STRUCTURE OF MU-PEROXO-BIS[(1,9-BIS(2-PYRIDYL)-2,5,8-TRIAZANONANE)COBALT(III)] TETRAIODIDE - EFFECT OF CHELATE RING SIZE ON THE STRUCTURES AND STABILITIES OF DIOXYGEN COMPLEXES
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abstract
The structure of -peroxo-bis[(l, 9-bis(2-pyridyl)-2, 5, 8-triazanonane)cobalt(III)] tetraiodide, [Co(PYDIEN)]2O2I4, Co2C32H46N10O2I4, has been determined by single-crystal X-ray diffraction. The opaque crystals are orthorhombic, conforming to the space group Fdd2, with unit cell dimensions a = 26.73 (2) , b = 32.19 (1) , and c = 10.049 (6) ; Z = 8. The observed density of 1.90 (1) g cm3 agrees well with the calculated value of 1.89 g-cm-3. Least-squares refinement gave an R index of 0.045 for 2167 observed reflections with intensities greater than 3. The 0-0 distance of 1.489 (8) and the Co-O-O angle of 112.5 (4) are characteristic of peroxide bound to tripositive cobalt. The two pyridyl groups and the dioxygen moiety are cis to one another, the central (aliphatic) nitrogen donor of the ligand is trans to a pyridyl ring, and one of the secondary amino groups is trans to dioxygen in the distorted octahedral complex. The results of the structure determination provide an explanation for the difference in the oxygen affinities of [Co(PYDIEN)]2+ and the cobaltous complex of 1,1 l-bis(2-pyridyl)-2, 6, 10-triazaundecane (PYDPT). Some of the Co-N bonds in [Co(PYDIEN)]202I4 are shorter and thus stronger than those in [Co(PYDPT)]2O2I4-3H2O, the structure of which has been reported previously. Donation of electron density from the ligand to cobalt increases the tendency of cobalt to transfer electron density to dioxygen and is probably the major factor affecting the stability of the oxygen complex. That the extent of donation from cobalt to dioxygen is different in the two structures can be seen by comparison of the Co-O and O-O bond distances. 1979, American Chemical Society. All rights reserved.
