Powders of 1-Ce, 1-Nd and 1-U were finely ground in a glovebox, and 1-2 cm of each sample was loaded into to a 4 mm outer diameter (OD) quartz tube and sealed under vacuum. A solution of 1-Nd in 2-Me-THF (15 mM) was prepared in a glovebox. Quartz tubes of OD 4 mm were filled with ~3 cm of solution, which was immediately frozen and flamesealed under vacuum, and then rapidly transferred to the spectrometer within ca. 15 mins. Spectra were obtained at base temperature (4-7 K) and powder spectra were obtained for two rotations at ~90 degrees to one another to identify any features due to polycrystallinity. The field was corrected using a strong pitch sample (g = 2.0028). Spectra were simulated in EasySpin 6.0.0-dev.51. Powder spectra of 1-Ce and 1-Nd were simulated in the EasySpin function pepper as an effective S = ½, with rhombic g values, g = [g1, g2, g3] and gStrains (distribution of g values) to account for all line broadenings effects. For 1-Nd, g3 was not observed (< 0.4) and so was fixed to 0.2. Hyperfine coupling on the g1 feature (A1) for 1-Nd was included for the most abundant isotope and scaled for other isotopes based on nuclear g-factors.