The EPR data show that the ligand environment not only influences the population of the LS state, with [Co(1)](ClO4)2 >> [Co(3)](ClO4)2 > [Co(2)](ClO4)2, mirroring the trend predicted from the calculations, but that it affects the coordination environment of the HS state, in line with the SCXRD data. Importantly, the EPR data demonstrate experimentally that the HS configuration in complexes [Co(1-3)](ClO4)2 exhibits a large negative zero-field splitting (with D < -15 cm -1 ), in line with the predictions for the de novo models.