Syntheses,structure and properties of cobalt-(II) and -(III) complexes of pentadentate N_4S ligands with appended pyrazolyl groups: evidence for cobalt(II)-dioxygen reversible binding

摘要

Cobalt-(Il) and -(III) complexes ofpentadentate N4S ligands based on methyI2-aminocyclopent-l-ene-l-carbo- ithioate with appended pyrazolyl groups (3,5-Me2C3HN2CH2)2NCH(R)CH2NHC5H6C(=S)SCH3 (R = H, Hmmecd; 'H3, Hmmpcd) have been prepared and characterised by J.R, IH NMR and electronic spectroscopy. Two of these :>mpounds have also structurally been characterised by X-ray single crystal diffraction analyses.Cob~(II) in :o(mmpcd)]CIO4, I, shows a five-coordinate, trigonal bipyramidal geometry while its cobalt(III) counterpart, :o(mmpcd)CI]CIO4, 2, reveals a six-coordinated distorted octahedral structure by the Inclusion of a chloride ligand I its equatorial plane. In dmf or acetonitrile solution, I can bind dioxygen reversibly as indicated by EPR spectra :corded at cryogenic temperatures. Metal-dioxygen binding in I appears to be weak, possibly due to its trigonal ipyramidal structure and the presence of a sulfur donor in the ligand framework. Electronic spectra of the obalt(llI) complexes show two LMCT bands in the near UV region, tentatively assigned to S-.Co1l1 charge transfer.