Minimal active space CASSCF-SO calculations were performed on all paramagnetic 1-Ln using OpenMolcas and the molecular structures from single crystal XRD data, in order to probe their electronic structures (see Experimental Section for details, Supporting Information Figures S61-S64 and Tables ). The active spaces consist of seven 4f orbitals with the appropriate number of electrons in each case. A mixed ground state is observed for 1-Ce (gz = 3.498, 78% mJ = ±5/2), as gz is tilted away from the O-Ce-O pseudo-axis; the calculated g-value is in good agreement with that determined by EPR spectroscopy (see above). By contrast, the ground state for 1-Pr is a more pure 97% mJ = ±4 and ∓4 pseudo-doublet, with a splitting of 0.9 cm -1 and the principal magnetic axis approximately coincident with O-Pr-O. Similarly, the gz axis of 1-Nd is aligned along O-Nd-O and the ground state is quite pure (gz = 5.874, 89% mJ = ±9/2), in good agreement with experiment (see above). Finally, for 1-Sm the ground state is calculated to be 87% mJ soft formally negatively charged P-donors of {P(SiMe3)2} in defining the anisotropy of the complexes; for the more magnetic 1-Pr and 1-Nd the O-atoms dominate, while this is less clear-cut for 1-Ce and 1-Sm.