Venturing\nPast Uranium: Synthesis of a Np(IV) Polyoxomolybdate–Alkoxide\nSandwich Complex

The synthesis of a Np(IV) polyoxomolybdate–alkoxide\nsandwich\ncomplex, (TBA)<sub>2</sub>[Np{Mo<sub>5</sub>O<sub>13</sub>(OMe)<sub>4</sub>NO}<sub>2</sub>] (TBA = tetrabutylammonium), is reported.\nThis compound represents a rare example of a neptunium polyoxometalate\ncluster isolated outside of water, allowing for characterization of\nits electrochemical properties in nonaqueous solvents. Complexation\nof An(IV) cations fine-tunes the redox properties of the cluster,\nwith the observed four reversible reductive events varying slightly\nboth in potential and peak separation depending on the actinide present.\nThe new Np(IV) complex also shows an irreversible event assigned to\noxidation of Np(IV) to Np(V). New methodology for facile <sup>17</sup>O enrichment of (TBA)<sub>2</sub>[Mo<sub>5</sub>O<sub>13</sub>(OMe)<sub>4</sub>NO][Na(MeOH)] is presented, which provides a simple pathway\nto <sup>17</sup>O enriched analogues of the sandwich complexes discussed\n(Zr(IV), Hf(IV), Th(IV), U(IV), U(V), Np(IV)). <sup>17</sup>O NMR\nspectroscopy subsequently provides insights into both the nature of\nmetal–oxygen bonding, as well as the influence of unpaired\nf-electrons on the local environment of the oxygen nuclei.