Electronic Structure of Cobalt–Corrole–Pyridine Complexes: Noninnocent Five-Coordinate Co(II) Corrole–Radical States
journal contributionposted on 11.12.2017, 15:06 by Sumit Ganguly, Jeanet Conradie, Jesper Bendix, Kevin J. Gagnon, Laura J. McCormick, Abhik Ghosh
Two sets of complexes of Co–triarylcorrole–bispyridine complexes, Co[TpXPC](py)2 and Co[Br8TpXPC](py)2 have been synthesized, where TpXPC refers to a meso-tris(para-X-phenyl)corrole ligand with X = CF3, H, Me, and OMe and Br8TpXPC to the corresponding β-octabrominated ligand. The axial pyridines in these complexes were found to be labile and, in dilute solutions in dichloromethane, the complexes dissociate almost completely to the five-coordinate monopyridine complexes. Upon addition of a small quantity of pyridine, the complexes revert back to the six-coordinate forms. These transformations are accompanied by dramatic changes in color and optical spectra. 1H NMR spectroscopy and X-ray crystallography have confirmed that the bispyridine complexes are authentic low-spin Co(III) species. Strong substituent effects on the Soret maxima and broken-symmetry DFT calculations, however, indicate a CoII–corrole•2– formulation for the five-coordinate Co[TpXPC](py) series. The calculations implicate a Co(dz2)–corrole(“a2u”) orbital interaction as responsible for the metal–ligand antiferromagnetic coupling that leads to the open-shell singlet ground state of these species. Furthermore, the calculations predict two low-energy S = 1 intermediate-spin Co(III) states, a scenario that we have been able to experimentally corroborate with temperature-dependent EPR studies. Our findings add to the growing body of evidence for noninnocent electronic structures among first-row transition metal corrole derivatives.
Read the peer-reviewed publication
open-shell singlet ground statelow-energy S1 H NMR spectroscopyT p XPCmonopyridine complexesBr 8 T p XPCIIbroken-symmetry DFT calculationsSoret maximaStrong substituent effectsX-ray crystallographyfirst-row transition metal corrole derivativesCobispyridine complexessix-coordinate formsβ- octabrominated ligandCF 3Electronic Structuretemperature-dependent EPR studies