Sm2SiO5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 9-coordinate geometry to one O(3), two equivalent O(1), three equivalent O(2), and three equivalent O(5) atoms. In the second Sm site, Sm(2) is bonded to one O(1), three equivalent O(3), and three equivalent O(4) atoms to form distorted SmO7 hexagonal pyramids that share corners with two equivalent Si(1)O4 tetrahedra, edges with six equivalent Sm(2)O7 hexagonal pyramids, and  an edgeedge with one Si(1)O4 tetrahedra. Si(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form SiO4 tetrahedra that share corners with two equivalent Sm(2)O7 hexagonal pyramids and  an edgeedge with one Sm(2)O7 hexagonal pyramid. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Sm(2), two equivalent Sm(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to three equivalent Sm(1) and one Si(1) atom. In the third O site, O(3) is bonded to one Sm(1) and three equivalent Sm(2) atoms to form a mixture of corner and edge-sharing OSm4 tetrahedra. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to three equivalent Sm(2) and one Si(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to three equivalent Sm(1) and one Si(1) atom.
Sm2SiO5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 9-coordinate geometry to one O(3), two equivalent O(1), three equivalent O(2), and three equivalent O(5) atoms. The Sm(1)-O(3) bond length is 2.38 Å. There is one shorter (2.33 Å) and one longer (2.52 Å) Sm(1)-O(1) bond length. There are a spread of Sm(1)-O(2) bond distances ranging from 2.46-2.74 Å. There are a spread of Sm(1)-O(5) bond distances ranging from 2.38-2.58 Å. In the second Sm site, Sm(2) is bonded to one O(1), three equivalent O(3), and three equivalent O(4) atoms to form distorted SmO7 hexagonal pyramids that share corners with two equivalent Si(1)O4 tetrahedra, edges with six equivalent Sm(2)O7 hexagonal pyramids, and  an edgeedge with one Si(1)O4 tetrahedra. The Sm(2)-O(1) bond length is 2.40 Å. There is one shorter (2.31 Å) and two longer (2.33 Å) Sm(2)-O(3) bond lengths. There are a spread of Sm(2)-O(4) bond distances ranging from 2.40-2.57 Å. Si(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form SiO4 tetrahedra that share corners with two equivalent Sm(2)O7 hexagonal pyramids and  an edgeedge with one Sm(2)O7 hexagonal pyramid. The Si(1)-O(1) bond length is 1.65 Å. The Si(1)-O(2) bond length is 1.60 Å. The Si(1)-O(4) bond length is 1.64 Å. The Si(1)-O(5) bond length is 1.63 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Sm(2), two equivalent Sm(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to three equivalent Sm(1) and one Si(1) atom. In the third O site, O(3) is bonded to one Sm(1) and three equivalent Sm(2) atoms to form a mixture of corner and edge-sharing OSm4 tetrahedra. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to three equivalent Sm(2) and one Si(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to three equivalent Sm(1) and one Si(1) atom.