title: A comparison of neptunyl(V) and neptunyl(VI) solution coordination: the stability of cation-cation interactions.
abstract: The solution coordination environments of pentavalent and hexavalent Np are studied by high-energy X-ray scattering. Np5+ and Np6+ both exist as the neptunyl moiety coordinated with five equatorial waters at Np-O distances of 2.46(2) and 2.37(2) A, respectively. NpO2(2+) also has a second coordination sphere of 6-10 waters at 4.37(3) A. The NpO2+ scattering is complicated by the presence of scattering at about 4.2 A that is attributed to Np-Np cation-cation interactions. The analysis of changing intensity of this peak as a function of Np concentration is used to determine a stability constant of Keq=0.74(9) M(-1) for the dimeric complex.
authors.affiliation: Heavy Elements and Separation Sciences Group, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: S
authors.initials: S
authors.lastname: Skanthakumar
authors.forename: Mark R
authors.initials: MR
authors.lastname: Antonio
authors.forename: L
authors.initials: L
authors.lastname: Soderholm