CASSCF calculations on 4-Ln using an active space of 7 × 4f orbitals and one TEMPO ), in excellent agreement with experiment (10,080 and 11,460 cm -1 ) and showing a similar splitting due to the CF as 2-Yb. The energies of excited 3 H4 and 3 F4 states seen in UV-vis-NIR spectra are confirmed to be virtually unchanged from 2-Tm to 4-Tm (Table ). The near-continuum of excited 6 H-and 6 F-derived states up to 13,500 cm -1 are also reproduced for 2-Sm and 4-Sm (Table ). Furthermore, the states derived from the Yb 3+ 2 F7/2 and Tm 3+ 6 H6 ground terms span a similar energy range in 2-Ln and 4-Ln. Comparison to calculations using the coordinates of the 4-Ln cations but treated as a neutral species with artificial Ln 3+ -TEMPO -charge distributions ([4-Ln] 0 ) can distinguish between effects of changing the geometry and changing the TEMPO -anion to a TEMPO • radical. Comparing 2-Ln and [4-Ln] 0 indicates geometry changes contribute only a minor increase in mixing and do not affect the approximate energies or ordering of the states; most CF parameters are changed by less than one order of magnitude (Table ). The introduction of the radical (4-Ln vs [4-Ln] 0 ) has a more significant effect on the CF: the first excited exchange multiplet is lowered in energy by 18% for Sm and Tm and 15% for Yb.