Article open access publication

Electronic Structure of Cobalt-Corrole-Pyridine Complexes: Noninnocent Five-Coordinate Co(II) Corrole-Radical States.

The Journal of Physical Chemistry A, American Chemical Society (ACS), ISSN 1089-5639

Volume 121, 50, 2017

DOI:10.1021/acs.jpca.7b09440, Dimensions: pub.1099739475, PMID: 29227102,



  1. (1) The Arctic University of Norway, grid.10919.30
  2. (2) University of the Free State, grid.412219.d
  3. (3) University of Copenhagen, grid.5254.6, KU
  4. (4) Lawrence Berkeley National Laboratory, grid.184769.5


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.


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