We have synthesised a family of Ln 3+ complexes [Ln(Cp tt )3] (1-Ln; Ln = La, Ce, Nd, Sm) using a salt metathesis route. The solid-state structures of 1-Ln reveal that the distances between the Ln 3+ centres and the Cp tt centroids decrease regularly from La 3+ to Sm 3+ due to the ionic radii of Ln 3+ ions decreasing across the series. Complexes 1-La and 1-Nd exhibit pseudotrigonal planar geometries, which is consistent with the previously reported structures of 1-Ce, 1-Sm and 1-Yb. Continuous wave and pulsed EPR studies were performed on 1-Nd, 1-Ce, and 1-Sm. The CW spectra show rhombic systems with anisotropic gvalues for both frozen solution and powder samples for 1-Nd and 1-Ce. HYSCORE spectroscopy shows resonances for C and 1 H regions for both 1-Nd and 1-Ce, and point-dipole simulations provide excellent agreement with experimental data. CASSCF-SO calculations effectively reproduce magnetic data, and fully-ab initio simulations of the HYSCORE spectra are also in excellent agreement with experiment, confirming minimal spin density at ligand nuclei. The larger ligand hyperfine interactions observed for 1-Th cf. 1-Ce are consistent with the 6d 1 vs. 4f 1 configurations of Th 3+ and Ce 3+ , respectively, and the significant radial extent of the 6d orbital(s). Comparing the results for 1-Nd with 1-U shows larger ligand hyperfines observed for the latter, highlighting the difference between 4f and 5f valence orbitals.