Continuous Wave (CW) X-band EPR spectra were recorded with a Bruker EMXPlus spectrometer with 1.8 T electromagnet and Stinger closed-cycle helium gas cryostat. Polycrystalline samples of 1-Ce and 1-Nd were sealed in quartz X-band EPR tubes under vacuum; samples were lightly ground with a mortar and pestle under inert atmosphere to reduce the amount of sample decomposition, but we note that some effects due to polycrystallinity remain in the 1-Nd spectra (identified by comparing two sample rotations at ~90 degrees to one another). Spectra were obtained at base temperature (7-16 K). The field was corrected using a strong pitch sample (g = 2.0028). Spectra were simulated in EasySpin 6.0.0-dev.48 using the pepper function. The ground doublet was simulated as an effective S = ½ with axial g-values (g = [gz, gxy, gxy]) and g-strains to phenomenologically account for all anisotropic line broadening effects. For Nd, a hyperfine coupling on the z-component was included in the model (A = [Az, 0, 0]), with the A axis assumed to be collinear with the g-axis. The hyperfine coupling constants are defined for the most abundant isotopes and scaled for other isotopes based on nuclear g-factors. Values used in the simulation are reported in Table .