2005 Volume 78 Issue 9 Pages 1619-1623
The reaction between a cobalt porphycene complex, [CoII(TPrPc)] (TPrPc is a dianion of 2,7,12,17-tetrapropylporphycene), and dioxygen was investigated by means of UV–vis, ESR, and resonance Raman (RR) spectroscopies. These spectra indicate the formation of [CoIII–O2−•]. In the presence of pyridine as an axial ligand, the formation of a six-coordinated superoxide species was confirmed by its characteristic ESR spectrum. The six-coordinated dioxygen adduct exhibits an RR band at 1144 cm−1, which is characteristic of O–O stretching of superoxide. ν(Co–O2) stretching is also observed at 540 cm−1. The ν(O–O) and ν(Co–O2) wavenumbers in the complex were assigned by means of 18O2 substitution. ν(Co–O2) of the O2 adduct shows a higher frequency relative to those of cobalt porphyrin complexes. On standing for one day at room temperature, the compound was auto-oxidized to a CoIII complex, which was structurally determined by X-ray analysis. The complex crystallized in the monoclinic space group P21/n, a = 9.6266(4) Å, b = 12.6343(5) Å, c = 15.6566(6) Å, β = 99.1200(10)°, V = 1880.17(13) Å3, and Z = 2. The CoIII ion lies on the plane of the porphycenato core, and coordinates four porphycenato nitrogen atoms and two pyridine nitrogen atoms. The complex cation, [CoIII(TPrPc)(Py)2]+, exhibits a slightly distorted octahedral coordination geometry. The average Co–N (porphycenato pyrrole) distance and the Co–N (pyridine) distance are 1.929 and 1.952 Å, respectively.
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