Understanding actinide chemistry is critical for nuclear waste treatment as well as for illuminating the role of f orbitals in bonding and reactivity. Researchers have made a leap forward in neptunium chemistry, preparing the first NpII and NpIII organometallic complexes (Nat. Chem. 2016, DOI: 10.1038/nchem.2520). Working at the Institute for Transuranium Elements, a team led by Polly L. Arnold of the University of Edinburgh combined radioactive NpCl4 and a macrocyclic ligand, trans-calixbenzenepyrrole, to form a mononuclear NpIII complex with the Np bound to the nitrogens of the pyrrole groups and sandwiched between the aryl rings; a fifth bond goes to Cl. The researchers reduced the complex to form a similar NpII structure in which the Cl is replaced by a neutral molecule of the solvent, dimethoxyethane, bound through its oxygens via a bidentate linkage. The NpII complex decays to a binuclear NpIII complex. Analysis of the mononuclear NpIII complex indicates that its bonds are more covalent than those in the analogous uranium(III) complex, with the covalency arising from spatial overlap of orbitals, the team says.