NpSe3 crystallizes in the tetragonal I4/mmm space group. Np(1) is bonded to four equivalent Se(2) and eight equivalent Se(1) atoms to form a mixture of edge, corner, and face-sharing NpSe12 cuboctahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 8-coordinate geometry to four equivalent Np(1) and four equivalent Se(1) atoms. In the second Se site, Se(2) is bonded in a square co-planar geometry to four equivalent Np(1) atoms.
NpSe3 crystallizes in the tetragonal I4/mmm space group. Np(1) is bonded to four equivalent Se(2) and eight equivalent Se(1) atoms to form a mixture of edge, corner, and face-sharing NpSe12 cuboctahedra. All Np(1)-Se(2) bond lengths are 2.91 Å. All Np(1)-Se(1) bond lengths are 3.21 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 8-coordinate geometry to four equivalent Np(1) and four equivalent Se(1) atoms. All Se(1)-Se(1) bond lengths are 2.91 Å. In the second Se site, Se(2) is bonded in a square co-planar geometry to four equivalent Np(1) atoms.