Sm2Pb2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded to one O(3), one O(4), one O(5), two equivalent O(2), and two equivalent O(6) atoms to form distorted SmO7 pentagonal bipyramids that share corners with two equivalent Pb(2)O6 octahedra, corners with two equivalent Sm(1)O7 pentagonal bipyramids, corners with two equivalent Pb(1)O5 square pyramids,  an edgeedge with one Pb(2)O6 octahedra,  an edgeedge with one Sm(1)O7 pentagonal bipyramid, and  an edgeedge with one Pb(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 40-53°. In the second Sm site, Sm(2) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. There are two inequivalent Pb sites. In the first Pb site, Pb(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(7) atom to form distorted PbO5 square pyramids that share corners with two equivalent Pb(2)O6 octahedra, corners with two equivalent Sm(1)O7 pentagonal bipyramids,  an edgeedge with one Pb(2)O6 octahedra, and  an edgeedge with one Sm(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 41-44°. In the second Pb site, Pb(2) is bonded to one O(4), one O(5), one O(6), one O(7), and two equivalent O(1) atoms to form distorted PbO6 octahedra that share corners with two equivalent Sm(1)O7 pentagonal bipyramids, corners with two equivalent Pb(1)O5 square pyramids,  an edgeedge with one Pb(2)O6 octahedra,  an edgeedge with one Sm(1)O7 pentagonal bipyramid, and  an edgeedge with one Pb(1)O5 square pyramid. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted see-saw-like geometry to one Sm(2), one Pb(1), and two equivalent Pb(2) atoms. In the second O site, O(2) is bonded to one Sm(2), two equivalent Sm(1), and one Pb(1) atom to form a mixture of edge and corner-sharing OSm3Pb tetrahedra. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Sm(1), one Sm(2), and one Pb(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Sm(1), one Sm(2), one Pb(1), and one Pb(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Sm(1), one Sm(2), and one Pb(2) atom. In the sixth O site, O(6) is bonded to one Sm(2), two equivalent Sm(1), and one Pb(2) atom to form a mixture of edge and corner-sharing OSm3Pb trigonal pyramids. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Sm(2), one Pb(1), and one Pb(2) atom.
Sm2Pb2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded to one O(3), one O(4), one O(5), two equivalent O(2), and two equivalent O(6) atoms to form distorted SmO7 pentagonal bipyramids that share corners with two equivalent Pb(2)O6 octahedra, corners with two equivalent Sm(1)O7 pentagonal bipyramids, corners with two equivalent Pb(1)O5 square pyramids,  an edgeedge with one Pb(2)O6 octahedra,  an edgeedge with one Sm(1)O7 pentagonal bipyramid, and  an edgeedge with one Pb(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 40-53°. The Sm(1)-O(3) bond length is 2.29 Å. The Sm(1)-O(4) bond length is 2.49 Å. The Sm(1)-O(5) bond length is 2.36 Å. There is one shorter (2.44 Å) and one longer (2.53 Å) Sm(1)-O(2) bond length. There is one shorter (2.41 Å) and one longer (2.46 Å) Sm(1)-O(6) bond length. In the second Sm site, Sm(2) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. The Sm(2)-O(1) bond length is 2.43 Å. The Sm(2)-O(2) bond length is 2.34 Å. The Sm(2)-O(3) bond length is 2.36 Å. The Sm(2)-O(4) bond length is 2.95 Å. The Sm(2)-O(5) bond length is 2.33 Å. The Sm(2)-O(6) bond length is 2.44 Å. The Sm(2)-O(7) bond length is 2.36 Å. There are two inequivalent Pb sites. In the first Pb site, Pb(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(7) atom to form distorted PbO5 square pyramids that share corners with two equivalent Pb(2)O6 octahedra, corners with two equivalent Sm(1)O7 pentagonal bipyramids,  an edgeedge with one Pb(2)O6 octahedra, and  an edgeedge with one Sm(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 41-44°. The Pb(1)-O(1) bond length is 2.23 Å. The Pb(1)-O(2) bond length is 2.15 Å. The Pb(1)-O(3) bond length is 2.15 Å. The Pb(1)-O(4) bond length is 2.15 Å. The Pb(1)-O(7) bond length is 2.22 Å. In the second Pb site, Pb(2) is bonded to one O(4), one O(5), one O(6), one O(7), and two equivalent O(1) atoms to form distorted PbO6 octahedra that share corners with two equivalent Sm(1)O7 pentagonal bipyramids, corners with two equivalent Pb(1)O5 square pyramids,  an edgeedge with one Pb(2)O6 octahedra,  an edgeedge with one Sm(1)O7 pentagonal bipyramid, and  an edgeedge with one Pb(1)O5 square pyramid. The Pb(2)-O(4) bond length is 2.23 Å. The Pb(2)-O(5) bond length is 2.07 Å. The Pb(2)-O(6) bond length is 2.21 Å. The Pb(2)-O(7) bond length is 2.17 Å. There is one shorter (2.30 Å) and one longer (2.43 Å) Pb(2)-O(1) bond length. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted see-saw-like geometry to one Sm(2), one Pb(1), and two equivalent Pb(2) atoms. In the second O site, O(2) is bonded to one Sm(2), two equivalent Sm(1), and one Pb(1) atom to form a mixture of edge and corner-sharing OSm3Pb tetrahedra. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Sm(1), one Sm(2), and one Pb(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Sm(1), one Sm(2), one Pb(1), and one Pb(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Sm(1), one Sm(2), and one Pb(2) atom. In the sixth O site, O(6) is bonded to one Sm(2), two equivalent Sm(1), and one Pb(2) atom to form a mixture of edge and corner-sharing OSm3Pb trigonal pyramids. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Sm(2), one Pb(1), and one Pb(2) atom.