CASSCF-SO and XMS-CASPT2 calculations were performed in OpenMolcas using 18.09 (tag: 790-g23d48b3-dirty) for Tm and Sm complexes, and version 20.10 (tag: 268-g4ac74574-dirty) for Yb complexes. The single crystal XRD coordinates were used with no optimization, in the case of disorder, the major component was selected. For 2-Ln, the complete molecule in the asymmetric unit with no local symmetry was selected. For 4-Ln, calculations were performed on the cationic [M(N † † )2(TEMPO)] + fragment and on the same coordinates with an artificial Ln(III)-TEMPO -charge distribution ([4-Ln] 0 ). Integrals were performed in SEWARD using basis sets from the ANO-RCC library with VTZP quality for Ln atoms, VDZP quality for coordinating N atoms and the N and O atoms of TEMPO, and VDZ quality for all other atoms, employing the second order DKH transformation. Cholesky decomposition of the two-electron integrals with a threshold of 10 -8 was performed to save disk space and reduce computational demand.