Mixed-Valent Neptunium(IV/V) Compound with Cation–Cation-Bound Six-Membered Neptunyl Rings

A new mixed-valent neptunium­(IV/V) compound has been synthesized by evaporation of a neptunium­(V) acidic solution. The structure of the compound features cation–cation-bound six-membered neptunyl­(V) rings. These rings are further connected by NpIV ions through cation–cation interactions (CCIs) into a three-dimensional neptunium cationic open framework. This example illustrates the possibility of isolating neptunyl­(V) CCI oligomers in inorganic systems using other cations to compete with NpV in bonding with the neptunyl oxygen.