Na3Sm2(SiSe3)2 crystallizes in the monoclinic C2/m space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form distorted NaSe6 octahedra that share corners with four equivalent Sm(1)Se6 octahedra, edges with four equivalent Sm(1)Se6 octahedra, and edges with six equivalent Na(2)Se6 octahedra. The corner-sharing octahedral tilt angles are 3°. In the second Na site, Na(2) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form distorted NaSe6 octahedra that share corners with four equivalent Sm(1)Se6 octahedra, edges with three equivalent Na(1)Se6 octahedra, edges with three equivalent Na(2)Se6 octahedra, and edges with four equivalent Sm(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-3°. Sm(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form SmSe6 octahedra that share corners with two equivalent Na(1)Se6 octahedra, corners with four equivalent Na(2)Se6 octahedra, edges with two equivalent Na(1)Se6 octahedra, edges with three equivalent Sm(1)Se6 octahedra, and edges with four equivalent Na(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-3°. Si(1) is bonded in a 3-coordinate geometry to one Se(1) and two equivalent Se(2) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to one Na(1), two equivalent Na(2), two equivalent Sm(1), and one Si(1) atom to form a mixture of corner and edge-sharing SeNa3Sm2Si octahedra. The corner-sharing octahedral tilt angles range from 0-88°. In the second Se site, Se(2) is bonded to one Na(1), two equivalent Na(2), two equivalent Sm(1), and one Si(1) atom to form a mixture of corner and edge-sharing SeNa3Sm2Si octahedra. The corner-sharing octahedral tilt angles range from 0-88°.
Na3Sm2(SiSe3)2 crystallizes in the monoclinic C2/m space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form distorted NaSe6 octahedra that share corners with four equivalent Sm(1)Se6 octahedra, edges with four equivalent Sm(1)Se6 octahedra, and edges with six equivalent Na(2)Se6 octahedra. The corner-sharing octahedral tilt angles are 3°. Both Na(1)-Se(1) bond lengths are 3.04 Å. All Na(1)-Se(2) bond lengths are 3.15 Å. In the second Na site, Na(2) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form distorted NaSe6 octahedra that share corners with four equivalent Sm(1)Se6 octahedra, edges with three equivalent Na(1)Se6 octahedra, edges with three equivalent Na(2)Se6 octahedra, and edges with four equivalent Sm(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-3°. Both Na(2)-Se(1) bond lengths are 3.17 Å. There are two shorter (3.02 Å) and two longer (3.15 Å) Na(2)-Se(2) bond lengths. Sm(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form SmSe6 octahedra that share corners with two equivalent Na(1)Se6 octahedra, corners with four equivalent Na(2)Se6 octahedra, edges with two equivalent Na(1)Se6 octahedra, edges with three equivalent Sm(1)Se6 octahedra, and edges with four equivalent Na(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-3°. Both Sm(1)-Se(1) bond lengths are 2.96 Å. All Sm(1)-Se(2) bond lengths are 2.96 Å. Si(1) is bonded in a 3-coordinate geometry to one Se(1) and two equivalent Se(2) atoms. The Si(1)-Se(1) bond length is 2.58 Å. Both Si(1)-Se(2) bond lengths are 2.57 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to one Na(1), two equivalent Na(2), two equivalent Sm(1), and one Si(1) atom to form a mixture of corner and edge-sharing SeNa3Sm2Si octahedra. The corner-sharing octahedral tilt angles range from 0-88°. In the second Se site, Se(2) is bonded to one Na(1), two equivalent Na(2), two equivalent Sm(1), and one Si(1) atom to form a mixture of corner and edge-sharing SeNa3Sm2Si octahedra. The corner-sharing octahedral tilt angles range from 0-88°.