Use of Magnetic Circular Dichroism to Determine Axial Ligation for Some Sterically Encumbered Iron(II) Porphyrin Complexes

Article abstract of DOI:10.1021/ja00409a003

The application of magnetic circular dichroism (MCD) as a fingerprint method for determining the spin state and axial coordination environment of a number of synthetic ferrous porphyrin complexes has been examined.The appearance of the MCD spectrum is a function of the spin state and the nature of the axial ligand or ligands.When these variables remain constant, the band shapes in the Soret region, but not the intensities, do not differ significantly within the series of porphyrins investigated here.For any given axial ligand or ligands, provided that spectra have been measured for a known example of each possible spin state and coordination environment to serve as standards, the shape of the MCD Soret band can be used as a qualitative marker of these key parameters.This determination is made on the basis of a single spectrum, and the advantages over other methods derive from the unique simplicity of the measurement.The coordination chemistry at iron(II) in the family of capped, pocket, and cofacial porphyrins studied here, as followed by MCD, can be used to determine, in a semiquantitative manner, the effects of the steric control of coordination features specifically incorporated into these porphyrin molecules.The design features and the steric effects are discussed.The MCD spectra are presented in graphic and tabular form, and the advantages and limitations of MCD as employed here are considered.The preparation and characterization of a mixed-metal, free-base, cofacial porphyrin is presented.