Organometallic Neptunium Chemistry

Fifty years have passed since the foundation of organometallic neptunium chemistry, and yet only a handful of complexes have been reported, and even fewer have been fully characterized. Yet, increasingly, combined synthetic/spectroscopic/computational studies are demonstrating how covalently bonding, soft, carbocyclic organometallic ligands provide an excellent platform for advancing the fundamental understanding of the differences in orbital contributions and covalency in f-block metal-ligand bonding. Understanding the subtleties is the key to the safe handling and separations of the highly radioactive nuclei. This review describes the complexes that have been synthesized to date and presents a critical assessment of the successes and difficulties in their analysis and the bonding information they have provided. Because of increasing recent efforts to start new Np-capable air-sensitive inorganic chemistry laboratories, the importance of radioactivity, the basics of Np decay ramifications (including the radiochemical synthesis of one organometallic compound), and the available anhydrous starting materials are also surveyed. The review also highlights a range of instances in which important differences, in the chemical behavior between Np and its closest neighbors, uranium and plutonium, are found.