Na4PbSi2Se6 crystallizes in the monoclinic C2 space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form NaSe6 octahedra that share corners with two equivalent Na(4)Se6 octahedra, corners with two equivalent Pb(1)Se6 octahedra, corners with two equivalent Si(1)SiSe3 tetrahedra, edges with two equivalent Na(4)Se6 octahedra, edges with two equivalent Pb(1)Se6 octahedra, edges with three equivalent Na(2)Se6 octahedra, edges with three equivalent Na(3)Se6 octahedra, and edges with two equivalent Si(1)SiSe3 tetrahedra. The corner-sharing octahedral tilt angles are 7°. In the second Na site, Na(2) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form NaSe6 octahedra that share corners with two equivalent Na(4)Se6 octahedra, corners with two equivalent Pb(1)Se6 octahedra, corners with two equivalent Si(1)SiSe3 tetrahedra, edges with two equivalent Na(4)Se6 octahedra, edges with two equivalent Pb(1)Se6 octahedra, edges with three equivalent Na(1)Se6 octahedra, edges with three equivalent Na(3)Se6 octahedra, and edges with two equivalent Si(1)SiSe3 tetrahedra. The corner-sharing octahedral tilt angles range from 7-8°. In the third Na site, Na(3) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form NaSe6 octahedra that share corners with two equivalent Na(4)Se6 octahedra, corners with two equivalent Pb(1)Se6 octahedra, corners with two equivalent Si(1)SiSe3 tetrahedra, edges with two equivalent Na(4)Se6 octahedra, edges with two equivalent Pb(1)Se6 octahedra, edges with three equivalent Na(1)Se6 octahedra, edges with three equivalent Na(2)Se6 octahedra, and edges with two equivalent Si(1)SiSe3 tetrahedra. The corner-sharing octahedral tilt angles range from 7-8°. In the fourth Na site, Na(4) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form NaSe6 octahedra that share corners with two equivalent Na(1)Se6 octahedra, corners with two equivalent Na(2)Se6 octahedra, corners with two equivalent Na(3)Se6 octahedra, corners with six equivalent Si(1)SiSe3 tetrahedra, edges with two equivalent Na(1)Se6 octahedra, edges with two equivalent Na(2)Se6 octahedra, edges with two equivalent Na(3)Se6 octahedra, and edges with three equivalent Pb(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 7-8°. Pb(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form PbSe6 octahedra that share corners with two equivalent Na(1)Se6 octahedra, corners with two equivalent Na(2)Se6 octahedra, corners with two equivalent Na(3)Se6 octahedra, corners with six equivalent Si(1)SiSe3 tetrahedra, edges with two equivalent Na(1)Se6 octahedra, edges with two equivalent Na(2)Se6 octahedra, edges with two equivalent Na(3)Se6 octahedra, and edges with three equivalent Na(4)Se6 octahedra. The corner-sharing octahedral tilt angles range from 7-8°. Si(1) is bonded to one Si(1), one Se(1), one Se(2), and one Se(3) atom to form distorted SiSiSe3 tetrahedra that share  a cornercorner with one Na(1)Se6 octahedra,  a cornercorner with one Na(2)Se6 octahedra,  a cornercorner with one Na(3)Se6 octahedra,  a cornercorner with one Se(1)Na4SiPb octahedra,  a cornercorner with one Se(2)Na4SiPb octahedra,  a cornercorner with one Se(3)Na4SiPb octahedra, corners with three equivalent Na(4)Se6 octahedra, corners with three equivalent Pb(1)Se6 octahedra,  an edgeedge with one Na(1)Se6 octahedra,  an edgeedge with one Na(2)Se6 octahedra, and  an edgeedge with one Na(3)Se6 octahedra. The corner-sharing octahedral tilt angles range from 19-77°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Na(1), one Na(2), one Na(3), one Na(4), one Pb(1), and one Si(1) atom to form distorted SeNa4SiPb octahedra that share  a cornercorner with one Se(1)Na4SiPb octahedra, corners with three equivalent Se(2)Na4SiPb octahedra, corners with three equivalent Se(3)Na4SiPb octahedra,  a cornercorner with one Si(1)SiSe3 tetrahedra, edges with two equivalent Se(1)Na4SiPb octahedra, edges with four equivalent Se(2)Na4SiPb octahedra, and edges with four equivalent Se(3)Na4SiPb octahedra. The corner-sharing octahedral tilt angles range from 0-91°. In the second Se site, Se(2) is bonded to one Na(1), one Na(2), one Na(3), one Na(4), one Pb(1), and one Si(1) atom to form distorted SeNa4SiPb octahedra that share  a cornercorner with one Se(3)Na4SiPb octahedra, corners with three equivalent Se(1)Na4SiPb octahedra, corners with three equivalent Se(2)Na4SiPb octahedra,  a cornercorner with one Si(1)SiSe3 tetrahedra,  an edgeedge with one Se(2)Na4SiPb octahedra, edges with four equivalent Se(1)Na4SiPb octahedra, and edges with five equivalent Se(3)Na4SiPb octahedra. The corner-sharing octahedral tilt angles range from 0-91°. In the third Se site, Se(3) is bonded to one Na(1), one Na(2), one Na(3), one Na(4), one Pb(1), and one Si(1) atom to form distorted SeNa4SiPb octahedra that share  a cornercorner with one Se(2)Na4SiPb octahedra, corners with three equivalent Se(1)Na4SiPb octahedra, corners with three equivalent Se(3)Na4SiPb octahedra,  a cornercorner with one Si(1)SiSe3 tetrahedra,  an edgeedge with one Se(3)Na4SiPb octahedra, edges with four equivalent Se(1)Na4SiPb octahedra, and edges with five equivalent Se(2)Na4SiPb octahedra. The corner-sharing octahedral tilt angles range from 0-92°.
Na4PbSi2Se6 crystallizes in the monoclinic C2 space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form NaSe6 octahedra that share corners with two equivalent Na(4)Se6 octahedra, corners with two equivalent Pb(1)Se6 octahedra, corners with two equivalent Si(1)SiSe3 tetrahedra, edges with two equivalent Na(4)Se6 octahedra, edges with two equivalent Pb(1)Se6 octahedra, edges with three equivalent Na(2)Se6 octahedra, edges with three equivalent Na(3)Se6 octahedra, and edges with two equivalent Si(1)SiSe3 tetrahedra. The corner-sharing octahedral tilt angles are 7°. Both Na(1)-Se(1) bond lengths are 3.23 Å. Both Na(1)-Se(2) bond lengths are 3.01 Å. Both Na(1)-Se(3) bond lengths are 3.00 Å. In the second Na site, Na(2) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form NaSe6 octahedra that share corners with two equivalent Na(4)Se6 octahedra, corners with two equivalent Pb(1)Se6 octahedra, corners with two equivalent Si(1)SiSe3 tetrahedra, edges with two equivalent Na(4)Se6 octahedra, edges with two equivalent Pb(1)Se6 octahedra, edges with three equivalent Na(1)Se6 octahedra, edges with three equivalent Na(3)Se6 octahedra, and edges with two equivalent Si(1)SiSe3 tetrahedra. The corner-sharing octahedral tilt angles range from 7-8°. Both Na(2)-Se(1) bond lengths are 3.08 Å. Both Na(2)-Se(2) bond lengths are 3.01 Å. Both Na(2)-Se(3) bond lengths are 3.15 Å. In the third Na site, Na(3) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form NaSe6 octahedra that share corners with two equivalent Na(4)Se6 octahedra, corners with two equivalent Pb(1)Se6 octahedra, corners with two equivalent Si(1)SiSe3 tetrahedra, edges with two equivalent Na(4)Se6 octahedra, edges with two equivalent Pb(1)Se6 octahedra, edges with three equivalent Na(1)Se6 octahedra, edges with three equivalent Na(2)Se6 octahedra, and edges with two equivalent Si(1)SiSe3 tetrahedra. The corner-sharing octahedral tilt angles range from 7-8°. Both Na(3)-Se(1) bond lengths are 3.07 Å. Both Na(3)-Se(2) bond lengths are 3.15 Å. Both Na(3)-Se(3) bond lengths are 3.01 Å. In the fourth Na site, Na(4) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form NaSe6 octahedra that share corners with two equivalent Na(1)Se6 octahedra, corners with two equivalent Na(2)Se6 octahedra, corners with two equivalent Na(3)Se6 octahedra, corners with six equivalent Si(1)SiSe3 tetrahedra, edges with two equivalent Na(1)Se6 octahedra, edges with two equivalent Na(2)Se6 octahedra, edges with two equivalent Na(3)Se6 octahedra, and edges with three equivalent Pb(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 7-8°. Both Na(4)-Se(1) bond lengths are 3.10 Å. Both Na(4)-Se(2) bond lengths are 3.12 Å. Both Na(4)-Se(3) bond lengths are 3.12 Å. Pb(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form PbSe6 octahedra that share corners with two equivalent Na(1)Se6 octahedra, corners with two equivalent Na(2)Se6 octahedra, corners with two equivalent Na(3)Se6 octahedra, corners with six equivalent Si(1)SiSe3 tetrahedra, edges with two equivalent Na(1)Se6 octahedra, edges with two equivalent Na(2)Se6 octahedra, edges with two equivalent Na(3)Se6 octahedra, and edges with three equivalent Na(4)Se6 octahedra. The corner-sharing octahedral tilt angles range from 7-8°. Both Pb(1)-Se(1) bond lengths are 3.10 Å. Both Pb(1)-Se(2) bond lengths are 3.12 Å. Both Pb(1)-Se(3) bond lengths are 3.13 Å. Si(1) is bonded to one Si(1), one Se(1), one Se(2), and one Se(3) atom to form distorted SiSiSe3 tetrahedra that share  a cornercorner with one Na(1)Se6 octahedra,  a cornercorner with one Na(2)Se6 octahedra,  a cornercorner with one Na(3)Se6 octahedra,  a cornercorner with one Se(1)Na4SiPb octahedra,  a cornercorner with one Se(2)Na4SiPb octahedra,  a cornercorner with one Se(3)Na4SiPb octahedra, corners with three equivalent Na(4)Se6 octahedra, corners with three equivalent Pb(1)Se6 octahedra,  an edgeedge with one Na(1)Se6 octahedra,  an edgeedge with one Na(2)Se6 octahedra, and  an edgeedge with one Na(3)Se6 octahedra. The corner-sharing octahedral tilt angles range from 19-77°. The Si(1)-Si(1) bond length is 2.35 Å. The Si(1)-Se(1) bond length is 2.30 Å. The Si(1)-Se(2) bond length is 2.31 Å. The Si(1)-Se(3) bond length is 2.31 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Na(1), one Na(2), one Na(3), one Na(4), one Pb(1), and one Si(1) atom to form distorted SeNa4SiPb octahedra that share  a cornercorner with one Se(1)Na4SiPb octahedra, corners with three equivalent Se(2)Na4SiPb octahedra, corners with three equivalent Se(3)Na4SiPb octahedra,  a cornercorner with one Si(1)SiSe3 tetrahedra, edges with two equivalent Se(1)Na4SiPb octahedra, edges with four equivalent Se(2)Na4SiPb octahedra, and edges with four equivalent Se(3)Na4SiPb octahedra. The corner-sharing octahedral tilt angles range from 0-91°. In the second Se site, Se(2) is bonded to one Na(1), one Na(2), one Na(3), one Na(4), one Pb(1), and one Si(1) atom to form distorted SeNa4SiPb octahedra that share  a cornercorner with one Se(3)Na4SiPb octahedra, corners with three equivalent Se(1)Na4SiPb octahedra, corners with three equivalent Se(2)Na4SiPb octahedra,  a cornercorner with one Si(1)SiSe3 tetrahedra,  an edgeedge with one Se(2)Na4SiPb octahedra, edges with four equivalent Se(1)Na4SiPb octahedra, and edges with five equivalent Se(3)Na4SiPb octahedra. The corner-sharing octahedral tilt angles range from 0-91°. In the third Se site, Se(3) is bonded to one Na(1), one Na(2), one Na(3), one Na(4), one Pb(1), and one Si(1) atom to form distorted SeNa4SiPb octahedra that share  a cornercorner with one Se(2)Na4SiPb octahedra, corners with three equivalent Se(1)Na4SiPb octahedra, corners with three equivalent Se(3)Na4SiPb octahedra,  a cornercorner with one Si(1)SiSe3 tetrahedra,  an edgeedge with one Se(3)Na4SiPb octahedra, edges with four equivalent Se(1)Na4SiPb octahedra, and edges with five equivalent Se(2)Na4SiPb octahedra. The corner-sharing octahedral tilt angles range from 0-92°.