CRYSTAL AND MOLECULAR-STRUCTURE OF MU-PEROXO-BIS[1,11-BIS(2-PYRIDYL)-2,6,10-TRIAZAUNDECANE]COBALT(III) TETRAIODIDE TRIHYDRATE - COBALT DIOXYGEN COMPLEX OF A PENTADENTATE LIGAND

Single-crystal X-ray diffraction methods were employed to determine the structure of the reversible oxygen carrier μ-peroxo-bis{[1,11-bis(2-pyridyl)-2,6,10-triazaundecane]cobalt(III)} tetraiodide trihydrate, [Co(PYDPT)]2O2I4.3H2O, (CoN5C18H27)2O2I4.3H2O. The opaque crystals conform to the monoclinic space group P21/c with unit cell dimensions a=20.104 (9) Å,b-= 11.896 (5) Å, c = 21.899 (5) Å, and β = 116.33 (10)Δ; Z = 4. The observed density is 1.89 g cm-3 and the calculated density is 1.91 (1) g cm-3 Least-squares refinement with omission of hydrogen atoms gave an R index of 7.0% for 4191 reflections with intensities greater than 4σ. The pyridyl nitrogens are cis to one another and to the dioxygen bridge in the distorted octahedral geometry around the cobalt atoms, so that an imine nitrogen is trans to the dioxygen bridge. The O-O distance of 1.456 (9) Å is consistent with the formulation of the dioxygen group as a peroxide (O22-) ion and assignment of the tripositive oxidation state to the cobalt ions. The structure is compared with that of the analogous cobalt dioxygen complex containing disalicylaldehyde 3,3'-iminobis(propanimine) as a ligand for which the structure has been determined. The fact that the cobaltous complex of the analogous N-ethyl substituted ligand 1,11-bis(2-pyridyl)-6-ethyl-2,6,10-triazaundecane (PYEtDPT) does not react with molecular oxygen is attributed to steric hindrance at the oxygenation site. © 1979, American Chemical Society. All rights reserved.