The UV-vis spectra reflect several features related to the above-discussed details of the electronic structure, we describe these on the example of [Fe(4'-COOH-terpy)2] 2+ , displayed in Figure . It is clear from the side-by-side comparison that the calculated and measured UV-vis spectra show a fair qualitative agreement, which allows a confident assignment of the experimental spectral features, aiding the interpretation of the spectra. The observed agreement between theory and experiment holds for the whole series, as it is illustrated in the lower part of the figure, where the spec- Based on the TD-DFT calculations, the bands below 300 nm are assigned to ligand-centered (LC) transitions, while the stronger bands above 300 nm belong to MLCT transitions of different kinds. Many of these transitions are not pure in nature, as there is a diverse mixing of the empty and occupied 3d atomic orbitals and the π and π * orbitals of the ligands, in accordance with the different π-d mixings described in Ref. 14. This is particularly affecting the region between 300-360 nm, where the LC and MLCT characters are rather mixed. In addition, weak d-d excitations (with very little ligand contribution) are found at around 600 nm.