DOE OSTI2020
NpSe3 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Np6+ is bonded to twelve Se2- atoms to form NpSe12 cuboctahedra that share corners with four equivalent NpSe12 cuboctahedra, edges with eight equivalent NpSe12 cuboctahedra, edges with sixteen equivalent SeNp4Se8 cuboctahedra, faces with four equivalent NpSe12 cuboctahedra, and faces with eight equivalent SeNp4Se8 cuboctahedra. There are four shorter (2.91 Å) and eight longer (3.21 Å) Np–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to four equivalent Np6+ and eight Se2- atoms to form distorted SeNp4Se8 cuboctahedra that share corners with twelve equivalent SeNp4Se8 cuboctahedra, edges with eight equivalent NpSe12 cuboctahedra, edges with eight equivalent SeNp4Se8 cuboctahedra, faces with four equivalent NpSe12 cuboctahedra, and faces with ten equivalent SeNp4Se8 cuboctahedra. There are four shorter (2.91 Å) and four longer (3.21 Å) Se–Se bond lengths. In the second Se2- site, Se2- is bonded in a square co-planar geometry to four equivalent Np6+ and eight equivalent Se2- atoms.