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 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 g 3 axis directed perpendicular to the plane. The cobalt hyperfine matrix A has principal values A 1 Co = 72, A 2 Co = 8, A 3 Co = 10 MHz, with the A 3 Co and g 3 axes parallel to each other and the A 1 Co axis rotated from the g 1 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 d yz orbital.

Electronic Structure of Transition Metal−Isocorrole Complexes: A First Quantum Chemical Study

“…[25] The electronic structures of Co(IsoC)Ph and Co(Cor)Ph appear to be of particular interest. [26,27] First, the electron spin-density profiles (Figure 2) are qualitatively different from those found in the Mn and Fe complexes. Thus, the corrole [27] or isocorrole ligand in the cobalt complexes carries large amounts of majority spin; indeed, the single unpaired electron spin appears to be roughly evenly distributed between the Co center and the macrocycle in these complexes as a result of a Co(d π )Ϫmacrocycle(π) orbital interaction.…”

Bis-picket-fence corroles

“…1), and their metal complexes has been a fast growing field of research stimulated by their intriguing electronic structures and their numerous potential applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The basis for this development was provided by the introduction of new straightforward syntheses for mesoarylsubstituted corroles [15][16][17][18][19][20][21].…”

26.5–40 GHz Ka-band pulsed EPR spectrometer

“…The several published applications were mostly ESEEM, demonstrating that the K a band is indeed suitable for ESEEM spectroscopy (11)(12)(13). Both of the described spectrometers employed a high-power (ϳ100 W) traveling wave tube amplifier (TWTA), which allows one to obtain microwave fields 2␤B 1 ϳ 25 MHz in conventional volume resonators accommodating high-volume sample tubes with the outer diameter (OD) of 2.5-3 mm.…”