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).