The measured χT values of 1.45 and 0.75 cm 3 mol -1 K at 300 K for 1-Nd and 1-Ce, respectively (Figure ), are close to the expected values of 1.63 and 0.80 cm 3 mol - 1 K for Nd 3+ ( 4 I9/2) and Ce 3+ ( 2 F5/2). The χT product decreases gradually upon cooling until below 50 or 60 K, where it drops to reach 0.44 and 0.30 cm 3 mol -1 K at 1.8 K, respectively. For 1-Sm, χT is 0.20 cm 3 mol -1 K at 300 K, which is larger than expected for an isolated free-ion 6 H5/2 term of 0.09 cm 3 mol -1 K, owing to thermal population of the low-lying 6 H7/2 term. The decrease of χT in all cases is due to the depopulation of the crystal field states. Isothermal magnetisation measurements of all compounds deviate from values expected for pure Ising-like mJ states (Supplementary Information Figures ), indicating significant mixing of mJ states. To corroborate these results, we performed CASSCF-SO calculations using a minimal n-electrons in 7 orbital active space (where n = 1 for Ce 3+ , n = 3 for Nd 3+ and n = 5 for Sm 3+ ; see Supplementary Information for details) and the solidstate XRD geometries (Tables ). These give excellent reproductions of the magnetic data (Figures and) and confirm substantially mixed mJ states (Tables ); the ground Kramers doublet for 1-Ce is dominated by |mJ| = ½, with the first excited state at 105-135 cm -1 , while for 1-Nd the ground Kramers doublet is dominated by mJ = ±5/2 mixed with ∓7/2, with a first excited state at 26 cm -1 . For 1-Sm the ground Kramers doublet is dominated by mJ = ±3/2, with a first excited state at 400 cm -1 .