Elucidation of the Influence of the Jahn–Teller Effect on Iron(III) Phthalocyanine Complexes and Their Magneto(optical) Spectroscopy: Experimental and Theoretical Data

UV-vis and magnetic circular dichroism (MCD) spectroscopies were used to characterize electronic transitions in [Pc(2−)Fe(CN) 2 ] − and Pc(1−)Fe(CN) 2 (Pc(2-) and Pc(1-) are phthalocyanine dianion and cation-radical ligands, respectively). The expected splittings for the 2 E g and 3 E u ground-state Jahn–Teller distortions were investigated by DFT and TDDFT calculations. It was demonstrated that several Jahn–Teller distortions lead to energetically similar D 2h and C 2h point group structures, as well as structures significantly higher in energy. TDDFT calculations for both compounds suggest that metal-to-ligand charge-transfer (MLCT) transitions mostly contribute to the UV absorption region, while the visible absorption region is dominated by intraligand π–π* and ligand-to-metal charge-transfer (LMCT) transitions. Triplet-multiplet and charge-transfer (LMCT) excited states are also predicted in the NIR region. This work represents the first attempt to explore the influence of the Jahn–Teller distortions on geometry, electronic structure, energetics, and spectroscopy of the low-spin iron(III) phthalocyanines with degenerate ground states.