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 2Eg and 3Eu ground-state Jahn-Teller distortions were investigated by DFT and TDDFT calculations. It was demonstrated that several Jahn-Teller distortions lead to energetically similar D2h and C2h 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.