for details). The ground state for pNMR calculations. We calculated the pNMR shifts using two methods (see Experimental Section for details): (i) a point-dipole approximation based on the CASSCF-SO-calculated magnetic susceptibility tensor (pseudo-contact shift (PCS) approximation, 𝛿 PCS para ); and, (ii) a full sum-over-states expression derived from the derivative of the Helmholtz free energy (van den Heuvel and Soncini's method 𝛿 vdH-S para ). The latter method is calculated directly based on the CASSCF-SO wavefunction and implicitly includes all through-bond (i.e. contact) and through-space (i.e. pseudocontact) terms, as well as the relativistic paramagnetic spin-orbit (PSO) terms. To calculate the experimental paramagnetic shift 𝛿 exp para , we subtracted the diamagnetic NMR signals measured for 1-La from the respective signals in the paramagnetic compounds. We report calculated 𝛿 para values obtained by averaging the calculated shift for all atoms in the same chemical environment, to approximate conformational averaging in the solution phase. We performed calculations using the XRD structure as well as a gas-phase optimized geometry (which retains the same disposition of ligands as in the XRD structure), and model compounds with one or two THF molecules removed (see Experimental Section for details). Upon dissociation of one THF, the central M(Si)3 core slightly pyramidalizes and the M-Si bond lengths decrease, which becomes more pronounced when the second THF is displaced (see Supporting Information Tables ). As suspected, removing THF ligands from 1-M changes the magnetic anisotropy; this is most clearly observed in the effective g-values of the ground Kramers doublets in 1-Ce and 1-Nd, which change from easy-axis anisotropy when there are two THF ligands coordinated, to rhombic anisotropy with one THF, and finally to easy-plane anisotropy when both THF ligands are removed (see Supporting Information Tables and).