Product evolution in the Np(IV) fluorophosphate system

The reaction of 237NpO2 with Cs2CO3, Ga2O3, H3PO4, and HF under mild hydrothermal conditions leads to the formation of NpFPO4 after 4 days at 180 °C. Heating at 180 °C for an additional 6 days leads to the crystallization of Cs2Np2F7PO4 and NpF4. The Ga2O3 forms a GaPO4 matrix in which crystals of NpFPO4, Cs2Np2F7PO4, and NpF4 grow. Single crystal X-ray data reveal that the structure of NpFPO4 consists of Np(IV) centers bound by both fluoride and phosphate to yield [NpF2O6] distorted dodecahedra. These are linked by corner-sharing with fluoride and both corner- and edge-sharing with phosphate to yield a dense, three-dimensional network. The structure of Cs2Np2F7PO4 is complex and contains both distorted dodecahedral [NpO2F6] and tricapped trigonal prismatic [NpO2F7] environments around Np(IV) that are linked with each other through corner- and edge-sharing, and with the phosphate groups to create a three-dimensional structure. There are small channels extending down the a-axis in Cs2Np2F7PO4. Crystallographic data: NpFPO4, orthorhombic, space group Pnma, a=8.598(2), b=6.964(1), c=6.337(1) Å, Z=4, V=379.44(13) Å3, R(F)=3.53% for 40 parameters and 465 reflections with I>2σ(I) (T=193 K); Cs2Np2F7PO4, monoclinic, space group P21/c, a=8.8727(4), b=16.2778(7), c=7.8009(4) Å, β=112.656(1), Z=4, V=1039.73(8) Å3, R(F)=2.27% for 146 parameters and 2465 reflections with I>2σ(I) (T=193 K).

Graphical abstractTwo Np(IV) fluorophosphates, NpFPO4 and Cs2Np2F7PO4, have been prepared as single crystals under hydrothermal conditions. NpFPO4 crystallizes first, then reacts to yield Cs2Np2F7PO4 and finally yields NpF4. Single crystal X-ray structures of NpFPO4 and Cs2Np2F7PO4 show three-dimensional frameworks containing Np(IV) in both eight- and nine-coordinate environments.Figure optionsDownload full-size imageDownload as PowerPoint slide