Nd2PbSi2Se8 crystallizes in the monoclinic Cc space group. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), one Se(3), one Se(6), one Se(7), one Se(8), and two equivalent Se(4) atoms. In the second Nd site, Nd(2) is bonded in a 8-coordinate geometry to one Se(3), one Se(6), one Se(7), one Se(8), two equivalent Se(2), and two equivalent Se(5) atoms. Pb(1) is bonded in a 6-coordinate geometry to one Se(5), one Se(6), one Se(7), one Se(8), and two equivalent Se(1) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a tetrahedral geometry to one Se(1), one Se(2), one Se(3), and one Se(7) atom. In the second Si site, Si(2) is bonded in a tetrahedral geometry to one Se(4), one Se(5), one Se(6), and one Se(8) atom. There are eight inequivalent Se sites. In the first Se site, Se(7) is bonded in a 3-coordinate geometry to one Nd(1), one Nd(2), one Pb(1), and one Si(1) atom. In the second Se site, Se(8) is bonded in a 3-coordinate geometry to one Nd(1), one Nd(2), one Pb(1), and one Si(2) atom. In the third Se site, Se(1) is bonded in a distorted single-bond geometry to one Nd(1), two equivalent Pb(1), and one Si(1) atom. In the fourth Se site, Se(2) is bonded to one Nd(1), two equivalent Nd(2), and one Si(1) atom to form distorted SeNd3Si trigonal pyramids that share corners with two equivalent Se(5)Nd2SiPb trigonal pyramids, corners with two equivalent Se(2)Nd3Si trigonal pyramids, and  an edgeedge with one Se(5)Nd2SiPb trigonal pyramid. In the fifth Se site, Se(3) is bonded in a distorted T-shaped geometry to one Nd(1), one Nd(2), and one Si(1) atom. In the sixth Se site, Se(4) is bonded in a T-shaped geometry to two equivalent Nd(1) and one Si(2) atom. In the seventh Se site, Se(5) is bonded to two equivalent Nd(2), one Pb(1), and one Si(2) atom to form distorted SeNd2SiPb trigonal pyramids that share corners with two equivalent Se(5)Nd2SiPb trigonal pyramids, corners with two equivalent Se(2)Nd3Si trigonal pyramids, and  an edgeedge with one Se(2)Nd3Si trigonal pyramid. In the eighth Se site, Se(6) is bonded in a 4-coordinate geometry to one Nd(1), one Nd(2), one Pb(1), and one Si(2) atom.
Nd2PbSi2Se8 crystallizes in the monoclinic Cc space group. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), one Se(3), one Se(6), one Se(7), one Se(8), and two equivalent Se(4) atoms. The Nd(1)-Se(1) bond length is 3.29 Å. The Nd(1)-Se(2) bond length is 3.04 Å. The Nd(1)-Se(3) bond length is 3.10 Å. The Nd(1)-Se(6) bond length is 3.28 Å. The Nd(1)-Se(7) bond length is 3.21 Å. The Nd(1)-Se(8) bond length is 3.20 Å. There is one shorter (2.96 Å) and one longer (3.04 Å) Nd(1)-Se(4) bond length. In the second Nd site, Nd(2) is bonded in a 8-coordinate geometry to one Se(3), one Se(6), one Se(7), one Se(8), two equivalent Se(2), and two equivalent Se(5) atoms. The Nd(2)-Se(3) bond length is 2.96 Å. The Nd(2)-Se(6) bond length is 3.00 Å. The Nd(2)-Se(7) bond length is 3.17 Å. The Nd(2)-Se(8) bond length is 3.17 Å. There is one shorter (3.11 Å) and one longer (3.37 Å) Nd(2)-Se(2) bond length. There is one shorter (3.16 Å) and one longer (3.33 Å) Nd(2)-Se(5) bond length. Pb(1) is bonded in a 6-coordinate geometry to one Se(5), one Se(6), one Se(7), one Se(8), and two equivalent Se(1) atoms. The Pb(1)-Se(5) bond length is 3.03 Å. The Pb(1)-Se(6) bond length is 3.24 Å. The Pb(1)-Se(7) bond length is 3.34 Å. The Pb(1)-Se(8) bond length is 3.38 Å. There is one shorter (2.98 Å) and one longer (3.25 Å) Pb(1)-Se(1) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a tetrahedral geometry to one Se(1), one Se(2), one Se(3), and one Se(7) atom. The Si(1)-Se(1) bond length is 2.29 Å. The Si(1)-Se(2) bond length is 2.31 Å. The Si(1)-Se(3) bond length is 2.29 Å. The Si(1)-Se(7) bond length is 2.30 Å. In the second Si site, Si(2) is bonded in a tetrahedral geometry to one Se(4), one Se(5), one Se(6), and one Se(8) atom. The Si(2)-Se(4) bond length is 2.29 Å. The Si(2)-Se(5) bond length is 2.29 Å. The Si(2)-Se(6) bond length is 2.30 Å. The Si(2)-Se(8) bond length is 2.30 Å. There are eight inequivalent Se sites. In the first Se site, Se(7) is bonded in a 3-coordinate geometry to one Nd(1), one Nd(2), one Pb(1), and one Si(1) atom. In the second Se site, Se(8) is bonded in a 3-coordinate geometry to one Nd(1), one Nd(2), one Pb(1), and one Si(2) atom. In the third Se site, Se(1) is bonded in a distorted single-bond geometry to one Nd(1), two equivalent Pb(1), and one Si(1) atom. In the fourth Se site, Se(2) is bonded to one Nd(1), two equivalent Nd(2), and one Si(1) atom to form distorted SeNd3Si trigonal pyramids that share corners with two equivalent Se(5)Nd2SiPb trigonal pyramids, corners with two equivalent Se(2)Nd3Si trigonal pyramids, and  an edgeedge with one Se(5)Nd2SiPb trigonal pyramid. In the fifth Se site, Se(3) is bonded in a distorted T-shaped geometry to one Nd(1), one Nd(2), and one Si(1) atom. In the sixth Se site, Se(4) is bonded in a T-shaped geometry to two equivalent Nd(1) and one Si(2) atom. In the seventh Se site, Se(5) is bonded to two equivalent Nd(2), one Pb(1), and one Si(2) atom to form distorted SeNd2SiPb trigonal pyramids that share corners with two equivalent Se(5)Nd2SiPb trigonal pyramids, corners with two equivalent Se(2)Nd3Si trigonal pyramids, and  an edgeedge with one Se(2)Nd3Si trigonal pyramid. In the eighth Se site, Se(6) is bonded in a 4-coordinate geometry to one Nd(1), one Nd(2), one Pb(1), and one Si(2) atom.