Na(Nd2Se3)4 crystallizes in the tetragonal I-42d space group. Na(1) is bonded to four equivalent Se(1) and four equivalent Se(2) atoms to form distorted NaSe8 hexagonal bipyramids that share corners with eight equivalent Nd(1)Se8 hexagonal bipyramids, edges with four equivalent Nd(3)Se8 hexagonal bipyramids, faces with four equivalent Nd(1)Se8 hexagonal bipyramids, and faces with four equivalent Nd(2)Se8 hexagonal bipyramids. There are three inequivalent Nd sites. In the first Nd site, Nd(1) is bonded to two equivalent Se(2), three equivalent Se(1), and three equivalent Se(3) atoms to form distorted NdSe8 hexagonal bipyramids that share corners with two equivalent Na(1)Se8 hexagonal bipyramids, corners with two equivalent Nd(1)Se8 hexagonal bipyramids, corners with two equivalent Nd(2)Se8 hexagonal bipyramids, corners with two equivalent Nd(3)Se8 hexagonal bipyramids,  an edgeedge with one Nd(2)Se8 hexagonal bipyramid, edges with three equivalent Nd(1)Se8 hexagonal bipyramids,  a faceface with one Na(1)Se8 hexagonal bipyramid, faces with two equivalent Nd(1)Se8 hexagonal bipyramids, faces with two equivalent Nd(2)Se8 hexagonal bipyramids, and faces with three equivalent Nd(3)Se8 hexagonal bipyramids. In the second Nd site, Nd(2) is bonded to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms to form distorted NdSe8 hexagonal bipyramids that share corners with four equivalent Nd(1)Se8 hexagonal bipyramids, corners with four equivalent Nd(3)Se8 hexagonal bipyramids, edges with two equivalent Nd(1)Se8 hexagonal bipyramids, edges with two equivalent Nd(2)Se8 hexagonal bipyramids, faces with two equivalent Na(1)Se8 hexagonal bipyramids, faces with two equivalent Nd(3)Se8 hexagonal bipyramids, and faces with four equivalent Nd(1)Se8 hexagonal bipyramids. In the third Nd site, Nd(3) is bonded to two equivalent Se(1), two equivalent Se(2), and four equivalent Se(3) atoms to form distorted NdSe8 hexagonal bipyramids that share corners with four equivalent Nd(1)Se8 hexagonal bipyramids, corners with four equivalent Nd(2)Se8 hexagonal bipyramids, edges with two equivalent Na(1)Se8 hexagonal bipyramids, edges with two equivalent Nd(3)Se8 hexagonal bipyramids, faces with two equivalent Nd(2)Se8 hexagonal bipyramids, and faces with six equivalent Nd(1)Se8 hexagonal bipyramids. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Na(1), one Nd(2), one Nd(3), and three equivalent Nd(1) atoms to form distorted SeNaNd5 octahedra that share corners with four equivalent Se(1)NaNd5 octahedra, corners with four equivalent Se(2)NaNd5 octahedra, corners with seven equivalent Se(3)Nd6 octahedra,  an edgeedge with one Se(3)Nd6 octahedra, edges with two equivalent Se(1)NaNd5 octahedra, edges with three equivalent Se(2)NaNd5 octahedra,  a faceface with one Se(1)NaNd5 octahedra, faces with two equivalent Se(2)NaNd5 octahedra, and faces with two equivalent Se(3)Nd6 octahedra. The corner-sharing octahedral tilt angles range from 14-52°. In the second Se site, Se(2) is bonded to one Na(1), one Nd(3), two equivalent Nd(1), and two equivalent Nd(2) atoms to form distorted SeNaNd5 octahedra that share corners with four equivalent Se(1)NaNd5 octahedra, corners with five equivalent Se(3)Nd6 octahedra, corners with six equivalent Se(2)NaNd5 octahedra, edges with three equivalent Se(1)NaNd5 octahedra, edges with three equivalent Se(3)Nd6 octahedra,  a faceface with one Se(3)Nd6 octahedra, faces with two equivalent Se(1)NaNd5 octahedra, and faces with two equivalent Se(2)NaNd5 octahedra. The corner-sharing octahedral tilt angles range from 19-50°. In the third Se site, Se(3) is bonded to one Nd(2), two equivalent Nd(3), and three equivalent Nd(1) atoms to form distorted SeNd6 octahedra that share corners with three equivalent Se(3)Nd6 octahedra, corners with five equivalent Se(2)NaNd5 octahedra, corners with seven equivalent Se(1)NaNd5 octahedra,  an edgeedge with one Se(1)NaNd5 octahedra, edges with two equivalent Se(3)Nd6 octahedra, edges with three equivalent Se(2)NaNd5 octahedra,  a faceface with one Se(2)NaNd5 octahedra, faces with two equivalent Se(1)NaNd5 octahedra, and faces with two equivalent Se(3)Nd6 octahedra. The corner-sharing octahedral tilt angles range from 16-52°.
Na(Nd2Se3)4 crystallizes in the tetragonal I-42d space group. Na(1) is bonded to four equivalent Se(1) and four equivalent Se(2) atoms to form distorted NaSe8 hexagonal bipyramids that share corners with eight equivalent Nd(1)Se8 hexagonal bipyramids, edges with four equivalent Nd(3)Se8 hexagonal bipyramids, faces with four equivalent Nd(1)Se8 hexagonal bipyramids, and faces with four equivalent Nd(2)Se8 hexagonal bipyramids. All Na(1)-Se(1) bond lengths are 3.03 Å. All Na(1)-Se(2) bond lengths are 3.27 Å. There are three inequivalent Nd sites. In the first Nd site, Nd(1) is bonded to two equivalent Se(2), three equivalent Se(1), and three equivalent Se(3) atoms to form distorted NdSe8 hexagonal bipyramids that share corners with two equivalent Na(1)Se8 hexagonal bipyramids, corners with two equivalent Nd(1)Se8 hexagonal bipyramids, corners with two equivalent Nd(2)Se8 hexagonal bipyramids, corners with two equivalent Nd(3)Se8 hexagonal bipyramids,  an edgeedge with one Nd(2)Se8 hexagonal bipyramid, edges with three equivalent Nd(1)Se8 hexagonal bipyramids,  a faceface with one Na(1)Se8 hexagonal bipyramid, faces with two equivalent Nd(1)Se8 hexagonal bipyramids, faces with two equivalent Nd(2)Se8 hexagonal bipyramids, and faces with three equivalent Nd(3)Se8 hexagonal bipyramids. There is one shorter (2.97 Å) and one longer (3.21 Å) Nd(1)-Se(2) bond length. There are a spread of Nd(1)-Se(1) bond distances ranging from 3.00-3.17 Å. There are a spread of Nd(1)-Se(3) bond distances ranging from 3.01-3.23 Å. In the second Nd site, Nd(2) is bonded to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms to form distorted NdSe8 hexagonal bipyramids that share corners with four equivalent Nd(1)Se8 hexagonal bipyramids, corners with four equivalent Nd(3)Se8 hexagonal bipyramids, edges with two equivalent Nd(1)Se8 hexagonal bipyramids, edges with two equivalent Nd(2)Se8 hexagonal bipyramids, faces with two equivalent Na(1)Se8 hexagonal bipyramids, faces with two equivalent Nd(3)Se8 hexagonal bipyramids, and faces with four equivalent Nd(1)Se8 hexagonal bipyramids. Both Nd(2)-Se(1) bond lengths are 3.03 Å. Both Nd(2)-Se(3) bond lengths are 3.23 Å. There are two shorter (3.00 Å) and two longer (3.17 Å) Nd(2)-Se(2) bond lengths. In the third Nd site, Nd(3) is bonded to two equivalent Se(1), two equivalent Se(2), and four equivalent Se(3) atoms to form distorted NdSe8 hexagonal bipyramids that share corners with four equivalent Nd(1)Se8 hexagonal bipyramids, corners with four equivalent Nd(2)Se8 hexagonal bipyramids, edges with two equivalent Na(1)Se8 hexagonal bipyramids, edges with two equivalent Nd(3)Se8 hexagonal bipyramids, faces with two equivalent Nd(2)Se8 hexagonal bipyramids, and faces with six equivalent Nd(1)Se8 hexagonal bipyramids. Both Nd(3)-Se(1) bond lengths are 3.16 Å. Both Nd(3)-Se(2) bond lengths are 2.99 Å. There are two shorter (3.01 Å) and two longer (3.21 Å) Nd(3)-Se(3) bond lengths. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Na(1), one Nd(2), one Nd(3), and three equivalent Nd(1) atoms to form distorted SeNaNd5 octahedra that share corners with four equivalent Se(1)NaNd5 octahedra, corners with four equivalent Se(2)NaNd5 octahedra, corners with seven equivalent Se(3)Nd6 octahedra,  an edgeedge with one Se(3)Nd6 octahedra, edges with two equivalent Se(1)NaNd5 octahedra, edges with three equivalent Se(2)NaNd5 octahedra,  a faceface with one Se(1)NaNd5 octahedra, faces with two equivalent Se(2)NaNd5 octahedra, and faces with two equivalent Se(3)Nd6 octahedra. The corner-sharing octahedral tilt angles range from 14-52°. In the second Se site, Se(2) is bonded to one Na(1), one Nd(3), two equivalent Nd(1), and two equivalent Nd(2) atoms to form distorted SeNaNd5 octahedra that share corners with four equivalent Se(1)NaNd5 octahedra, corners with five equivalent Se(3)Nd6 octahedra, corners with six equivalent Se(2)NaNd5 octahedra, edges with three equivalent Se(1)NaNd5 octahedra, edges with three equivalent Se(3)Nd6 octahedra,  a faceface with one Se(3)Nd6 octahedra, faces with two equivalent Se(1)NaNd5 octahedra, and faces with two equivalent Se(2)NaNd5 octahedra. The corner-sharing octahedral tilt angles range from 19-50°. In the third Se site, Se(3) is bonded to one Nd(2), two equivalent Nd(3), and three equivalent Nd(1) atoms to form distorted SeNd6 octahedra that share corners with three equivalent Se(3)Nd6 octahedra, corners with five equivalent Se(2)NaNd5 octahedra, corners with seven equivalent Se(1)NaNd5 octahedra,  an edgeedge with one Se(1)NaNd5 octahedra, edges with two equivalent Se(3)Nd6 octahedra, edges with three equivalent Se(2)NaNd5 octahedra,  a faceface with one Se(2)NaNd5 octahedra, faces with two equivalent Se(1)NaNd5 octahedra, and faces with two equivalent Se(3)Nd6 octahedra. The corner-sharing octahedral tilt angles range from 16-52°.