Hard, soft, hot, cold

F Block Chemistry Efficient sequestration of radioactive americium (Am) ions remains a challenge in nuclear waste remediation. Part of the difficulty is that the ions have a similar size and charge to stable lanthanide ions. Goodwin et al. systematically explored whether differences in covalency might manifest when Am and neodymium (Nd) are coordinated by more or less polarizable ligands (often termed soft or hard). They compared the crystal structures and spectral and computational electronic properties of Am(III) and Nd(III) with soft selenium (Se) or hard oxygen ligands. The upshot was that Am showed signs of covalency with Se, whereas Nd did not. Angew. Chem. Int. Ed. 10.1002/anie.202017186 (2021).