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 (H-2 and C-13). 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 C-13, H-1 and H-2 nuclei, meso H-1 and H-2 nuclei, and ethyl H-1 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 g(1) = 1.9670, g(2) = 2.1122, and g(3)=2.0043, with the g(1) and g(2) axes pointing at the nitrogens of the corrole macrocycle and the 93 axis directed perpendicular to the plane. The cobalt hyperfine matrix A has principal values A(1)(Co) = 72, A(2Co) = 8, A(3)(Co) = 10 MHz, with the A(3)(Co) and 93 axes parallel to each other and the A(1)(Co) axis rotated from the g, axis by 45degrees, so that it points at the meso proton H10. Relatively large H-1 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 d(yz) orbital.
