An interesting comparison can be made between 1-Nd and its valence isoelectronic An 3+ analog 1-U. Complex 1-U has T1 and Tm times of 860 and 0.8 μs, measured at the EDFS maximum under similar conditions, compared to 5 and 0.5 μs for 1-Nd. Hence, T1 for the Ln 3+ 4f 3 complex is more than two orders of magnitude shorter than for its An 3+ 5f 3 analogue. In general, electron spin-lattice relaxation times are expected to decrease going down the Periodic Table, as modulation of the electronic structure by vibrational modes (which is a dominant factor for T1 relaxation in immobilised samples ) impacts the orbital angular momentum. This is connected to the spin via spin-orbit coupling (SOC), and SOC increases with atomic number; the values for for Nd 3+ and U 3+ are 900 and ca. 1700 cm -1 , respectively. It seems reasonable to assume that the slower T1 relaxation of 1-U is due to the partial quenching of the orbital angular momentum by the larger crystal field interaction for U 3+ cf. Nd 3+ . This is promising for future pulsed EPR studies of Ancontaining materials. The 4f 1 complex 1-Ce also has a much shorter T1 than its An 3+ analogue 1-Th (T1 ca. 21 ms under similar conditions): this is due to the orbital singlet 6d 1 configuration of 1-Th, compared to 5f 1 for 1-Ce.