title: Heptavalent Neptunium in a Gas-Phase Complex: (NpVIIO3+)(NO3-)2.
abstract: A central goal of chemistry is to achieve ultimate oxidation states, including in gas-phase complexes with no condensed phase perturbations. In the case of the actinide elements, the highest established oxidation states are labile Pu(VII) and somewhat more stable Np(VII). We have synthesized and characterized gas-phase AnO3(NO3)2-complexes for An = U, Np, and Pu by endothermic NO2elimination from AnO2(NO3)3-. It was previously demonstrated that the PuO3+core of PuO3(NO3)2-has a Pu-O•radical bond such that the oxidation state is Pu(VI); it follows that in UO3(NO3)2-it is the stable U(VI) oxidation state. On the basis of the relatively more facile synthesis of NpO3(NO3)2-, a Np(VII) oxidation state is inferred. This interpretation is substantiated by reactivity of the three complexes: NO2spontaneously adds to UO3(NO3)2-and PuO3(NO3)2-but not to NpO3(NO3)2-. This unreactive character is attributed to a Np(VII)O3+core with three stable Np═O bonds, this in contrast to reactive U-O•and Pu-O•radical bonds. The computed structures and reaction energies for the three AnO3(NO3)2-support the conclusion that the oxidation states are U(VI), Np(VII), and Pu(VI). The results establish the extreme Np(VII) oxidation state in a gas-phase complex, and demonstrate the inherently greater stability of Np(VII) versus Pu(VII).
authors.affiliation: Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Phuong D
authors.initials: PD
authors.lastname: Dau
authors.affiliation: SUBATECH, UMR CNRS 6457, IN2P3/EMN Nantes/Université de Nantes , 4 rue Alfred Kastler, BP 20722, 44307 Nantes Cedex 3, France.
authors.forename: Rémi
authors.initials: R
authors.lastname: Maurice
authors.affiliation: CEISAM, UMR CNRS 6230, Université de Nantes , 2 rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Renault
authors.affiliation: Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: John K
authors.initials: JK
authors.lastname: Gibson