A Pulse EPR and ENDOR Investigation of the Electronic Structure of a σ-Carbon-Bonded Cobalt(IV) Corrole

Abstract

In this contribution we present a continuous wave (CW), pulse electron paramagnetic resonance (EPR), and pulse electron nuclear double resonance (ENDOR) study of (OEC)Co(C6H5), where OEC is the trianion of 2,3,7,8,12,13,17,18-octaethylcorrole. To facilitate spectral assignments isotopic substitutions were employed (2H and 13C). From the analysis of the frozen solution CW EPR, ESEEM, and ENDOR spectra measured at X- and Q-band, we determined the electronic coupling parameters of the unpaired electron with the cobalt nucleus, corrole nitrogen nuclei, phenyl 13C, 1H and 2H nuclei, meso 1H and 2H nuclei, and ethyl 1H nuclei. Determination of the g matrix alignment in the molecular frame was achieved by successfully simulating the orientationally selective powder ENDOR spectra of the meso nuclei. The g principal values are g1 = 1.9670, g2 = 2.1122, and g3=2.0043, with the g1 and g2 axes pointing at the nitrogens of the corrole macrocycle and the g3 axis directed perpendicular to the plane. The cobalt hyperfine matrix A has principal values A1Co = 72, A2Co = 8, A3Co = 10 MHz, with the A3Co and g3 axes parallel to each other and the A1Co axis rotated from the g1 axis by 45°, so that it points at the meso proton H10. Relatively large 1H ENDOR couplings with the ethyl protons were observed, indicating that significant spin density also exists on the macrocycle. A good description of the electronic structure, consistent with the experimental data, was achieved using density functional theory simulations. Both the experimental and calculated data support the conclusion that there is significant spin density on both the macrocycle and in the cobalt dyz orbital.

A Pulse EPR and ENDOR Investigation of the Electronic Structure of a σ-Carbon-Bonded Cobalt(IV) Corrole

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Abstract

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