A Continuous Wave and Pulse EPR and ENDOR Investigation of Oxygenated Co(II) Corrin Complexes

Abstract

Heptamethyl cobyrinate perchlorate, [Cob(II)ester]ClO4, has the relevant structural features of base-off B12r, the reduced Co(II) form of vitamin B12. The reversible oxygenation behavior of this complex in different solvents is investigated using continuous wave (cw) EPR at X-band and compared with that of Co(II) porphyrin complexes. Furthermore, the influence of the addition of a nitrogen base (pyridine or 1-methylimidazole) to the solutions is investigated. To determine the electronic structure of the oxygenated complexes, different pulse electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) techniques are applied. The g and cobalt hyperfine matrix and their principal axes are determined using a combination of cw-EPR at X- and Q-band, ESE (electron spin−echo)-detected EPR at W-band and Davies-ENDOR at Q-band. The experimental g and cobalt hyperfine values are found to be sensitive to the change of solvent, addition of a nitrogen base, and change in the ring structure. From ...