SnPSe3 crystallizes in the monoclinic Pc space group. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to one Se(1), one Se(2), one Se(4), one Se(5), and one Se(6) atom to form distorted SnSe5 square pyramids that share  a cornercorner with one P(2)PSe3 tetrahedra, corners with two equivalent P(1)PSe3 tetrahedra, and  an edgeedge with one P(2)PSe3 tetrahedra. In the second Sn site, Sn(2) is bonded in a 5-coordinate geometry to one Se(2), one Se(3), one Se(4), one Se(5), and one Se(6) atom. There are two inequivalent P sites. In the first P site, P(1) is bonded to one P(2), one Se(3), one Se(4), and one Se(5) atom to form distorted PPSe3 tetrahedra that share corners with two equivalent Sn(1)Se5 square pyramids. In the second P site, P(2) is bonded to one P(1), one Se(1), one Se(2), and one Se(6) atom to form distorted PPSe3 tetrahedra that share  a cornercorner with one Sn(1)Se5 square pyramid and  an edgeedge with one Sn(1)Se5 square pyramid. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in an L-shaped geometry to one Sn(1) and one P(2) atom. In the second Se site, Se(2) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(2) atom. In the third Se site, Se(3) is bonded in an L-shaped geometry to one Sn(2) and one P(1) atom. In the fourth Se site, Se(4) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(1) atom. In the fifth Se site, Se(5) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(1) atom. In the sixth Se site, Se(6) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(2) atom.
SnPSe3 crystallizes in the monoclinic Pc space group. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to one Se(1), one Se(2), one Se(4), one Se(5), and one Se(6) atom to form distorted SnSe5 square pyramids that share  a cornercorner with one P(2)PSe3 tetrahedra, corners with two equivalent P(1)PSe3 tetrahedra, and  an edgeedge with one P(2)PSe3 tetrahedra. The Sn(1)-Se(1) bond length is 2.81 Å. The Sn(1)-Se(2) bond length is 3.00 Å. The Sn(1)-Se(4) bond length is 2.92 Å. The Sn(1)-Se(5) bond length is 3.27 Å. The Sn(1)-Se(6) bond length is 3.08 Å. In the second Sn site, Sn(2) is bonded in a 5-coordinate geometry to one Se(2), one Se(3), one Se(4), one Se(5), and one Se(6) atom. The Sn(2)-Se(2) bond length is 3.25 Å. The Sn(2)-Se(3) bond length is 2.80 Å. The Sn(2)-Se(4) bond length is 3.26 Å. The Sn(2)-Se(5) bond length is 2.84 Å. The Sn(2)-Se(6) bond length is 2.98 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one P(2), one Se(3), one Se(4), and one Se(5) atom to form distorted PPSe3 tetrahedra that share corners with two equivalent Sn(1)Se5 square pyramids. The P(1)-P(2) bond length is 2.25 Å. The P(1)-Se(3) bond length is 2.19 Å. The P(1)-Se(4) bond length is 2.19 Å. The P(1)-Se(5) bond length is 2.19 Å. In the second P site, P(2) is bonded to one P(1), one Se(1), one Se(2), and one Se(6) atom to form distorted PPSe3 tetrahedra that share  a cornercorner with one Sn(1)Se5 square pyramid and  an edgeedge with one Sn(1)Se5 square pyramid. The P(2)-Se(1) bond length is 2.19 Å. The P(2)-Se(2) bond length is 2.18 Å. The P(2)-Se(6) bond length is 2.21 Å. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in an L-shaped geometry to one Sn(1) and one P(2) atom. In the second Se site, Se(2) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(2) atom. In the third Se site, Se(3) is bonded in an L-shaped geometry to one Sn(2) and one P(1) atom. In the fourth Se site, Se(4) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(1) atom. In the fifth Se site, Se(5) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(1) atom. In the sixth Se site, Se(6) is bonded in a 3-coordinate geometry to one Sn(1), one Sn(2), and one P(2) atom.