Abstract
Three actinide(IV) phosphites and a NpIV phosphate, An IV(HPO3)2(H2O)2 (An = Th, U, Np) and Cs[Np(H1.5PO4)(PO4)]2, respectively, were synthesized using mild hydrothermal conditions. The first three phases are isotypic and were obtained using similar reaction conditions. Cs[Np(H1.5PO4)(PO4)]2 was synthesized using an analogous method to that of Np(HPO3) 2(H2O)2. However, this fourth phase is quite different in comparison to the other phases in both composition and structure. The structure of Cs[Np(H1.5PO4)(PO4)] 2 is constructed from double layers of neptunium(IV) phosphate with caesium cations in the interlayer region. In contrast, An(HPO3) 2(H2O)2 (An = Th, U, Np) form dense 3D networks. The actinide contraction is detected in variety of metrics obtained from single-crystal X-ray diffraction data. Changes in the oxidation state of the neptunium starting materials yield different products.