Elemental analysis results obtained for 1-Ln consistently gave low carbon values; this is attributed to their thermal sensitivity and carbide formation from incomplete combustion, as has previously been proposed for similar non-classical Ln(II) derivatized Cp R complexes. Despite repeated attempts to dissolve 1-Ln in d8-THF at -30 °C to collect 1 H and C NMR spectra and to determine solution phase magnetic susceptibility by the Evans method, the only signals observed corresponded to 2.2.2-cryptand and respective [Ln(Cp tt )3] precursors; this is attributed to both the paramagnetism of 1-Ln and their thermal sensitivity. Facile thermal decomposition also precluded the acquisition of reliable SQUID data for 1-Ln. However, ATR-IR spectra collected on microcrystalline samples of 1-Ln that were only briefly allowed to warm from -30 °C clearly showed a consistent set of absorptions for all 1-Ln (see Supporting Information Figures ), which differ from those seen for parent [Ln(Cp tt )3], indicating that the solid state samples showed similar bulk features. We were able to isolate mononuclear 2-Pr and the dinuclear Sm(III) complex 4 in sufficient quantities to characterize them by single crystal XRD, elemental analysis, 1 H NMR spectroscopy, Evans method solution magnetic susceptibility, ATR-IR spectroscopy, UV-Vis-NIR spectroscopy and SQUID magnetometry, whereas the sample of the dinuclear Nd(III) complex 3 was contaminated with [Nd(Cp tt )3] and was therefore subjected to a single crystal XRD study only (see Supporting Information for characterization data for 2-Pr, 3 and 4; ATR-IR and NMR spectroscopic data for 2-Pr and 4 are shown in Figures ).