Nitrate Complexes of Neptunium(V) with Alkali Metal Cations in the Outer Sphere

Abstract

Nitrate complexes of pentavalent neptunium with alkali cations in the outer sphere, with composition Li[NpO2(NO3)2]·2H2O (I), Na[NpO2(NO3)2]·2H2O (II), Cs3[NpO2(NO3)2]3·H2O (III), NaRb5[NpO2(NO3)2]6·4H2O (IV) were isolated in the crystalline form and examined by the method of X-ray diffraction analysis. The cation–cation (CC) interaction of NpO2+ ions occurs in the complexes to give square (I, II) or trigonal-hexagonal (II, IV) cation networks. Np atoms in I–IV structures have a coordination environment in the form of hexagonal bipyramids the equatorial plane of which is formed by oxygen atoms of two bidentate-cyclic nitrate ions and two neighboring NpO2+ cations. The high quality of the single crystal of compound II made it possible to perform a high-precision X-ray diffraction experiment (2θmax = 120°) and study for the first time for Np compound the electron density distribution ρ(r). The IR and electronic absorption spectrum of compound II are presented.