Low-temperature MCD studies of low-spin ferric complexes of tetramesitylporphyrinate: evidence for the novel (dxz, dyz)4(dxy)1 ground state which models the spectroscopic properties of heme d

The low-spin complexes of three ferric tetramesitylporphyrin (FeIIITMP) are investigated by low-temperature magnetic circular dichroism (MCD) spectroscopy. Complexes 1 and 2 have ground state electronic configurations of (dxy)2(dxz,dyz)3 although they exhibit near-infrared porphyrin(pi)-ferric(d) charge transfer (NIR-CT) bands of completely varied MCD intensities. Complex 3 has vertical ligands and axial EPR spectrum of abnormal g-values and low MCD transitions in NIR, ultraviolet and visible wavelengths, which are attributed to a new (dxz,dyz)4(dxy)1 ground state.