). There is good agreement between measured and calculated magnetization values, and the expected values for the free Eu(II) ion (4f 7 8 S7/2) for 1-Eu. However, there is poorer agreement between these values for 1-Sm (Sm(II) 4f F0) which is likely a consequence of mixing of low-lying 6 F excited states with the magnetic ground state. The saturation magnetization value for 1-Sm is lower than calculated, which indicates that the ground state is purer than the 80% mJ = 0 which is predicted by CASSCF, previously seen in [Sm(Cp tt )3] (Cp tt = C5H3 t Bu2-1,3). The absolute values of χMT and magnetization are over-predicted for 1-Eu by CASSCF however, the shape is accurately reproduced, showing no change in the value of χT upon a decrease in temperature, indicative of a spin-only system.