KCuP2Se5 crystallizes in the monoclinic P2_1/c space group. K(1) is bonded in a 9-coordinate geometry to one Se(4), one Se(5), two equivalent Se(2), two equivalent Se(3), and three equivalent Se(1) atoms. Cu(1) is bonded to one Se(2), one Se(3), and two equivalent Se(4) atoms to form CuSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent P(1)PSe3 tetrahedra, and corners with two equivalent P(2)PSe3 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one P(2), one Se(2), one Se(3), and one Se(5) atom to form distorted PPSe3 tetrahedra that share  a cornercorner with one P(2)PSe3 tetrahedra, corners with two equivalent Cu(1)Se4 tetrahedra, and  a cornercorner with one Se(4)KCu2P trigonal pyramid. In the second P site, P(2) is bonded to one P(1), one Se(1), one Se(4), and one Se(5) atom to form distorted PPSe3 tetrahedra that share  a cornercorner with one P(1)PSe3 tetrahedra and corners with two equivalent Cu(1)Se4 tetrahedra. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted see-saw-like geometry to three equivalent K(1) and one P(2) atom. In the second Se site, Se(2) is bonded in a 4-coordinate geometry to two equivalent K(1), one Cu(1), and one P(1) atom. In the third Se site, Se(3) is bonded in a 4-coordinate geometry to two equivalent K(1), one Cu(1), and one P(1) atom. In the fourth Se site, Se(4) is bonded to one K(1), two equivalent Cu(1), and one P(2) atom to form distorted SeKCu2P trigonal pyramids that share  a cornercorner with one P(1)PSe3 tetrahedra and corners with two equivalent Se(4)KCu2P trigonal pyramids. In the fifth Se site, Se(5) is bonded in a distorted water-like geometry to one K(1), one P(1), and one P(2) atom.
KCuP2Se5 crystallizes in the monoclinic P2_1/c space group. K(1) is bonded in a 9-coordinate geometry to one Se(4), one Se(5), two equivalent Se(2), two equivalent Se(3), and three equivalent Se(1) atoms. The K(1)-Se(4) bond length is 3.53 Å. The K(1)-Se(5) bond length is 3.82 Å. There is one shorter (3.51 Å) and one longer (3.71 Å) K(1)-Se(2) bond length. There is one shorter (3.48 Å) and one longer (3.63 Å) K(1)-Se(3) bond length. There are a spread of K(1)-Se(1) bond distances ranging from 3.44-3.55 Å. Cu(1) is bonded to one Se(2), one Se(3), and two equivalent Se(4) atoms to form CuSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent P(1)PSe3 tetrahedra, and corners with two equivalent P(2)PSe3 tetrahedra. The Cu(1)-Se(2) bond length is 2.45 Å. The Cu(1)-Se(3) bond length is 2.40 Å. There is one shorter (2.51 Å) and one longer (2.54 Å) Cu(1)-Se(4) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded to one P(2), one Se(2), one Se(3), and one Se(5) atom to form distorted PPSe3 tetrahedra that share  a cornercorner with one P(2)PSe3 tetrahedra, corners with two equivalent Cu(1)Se4 tetrahedra, and  a cornercorner with one Se(4)KCu2P trigonal pyramid. The P(1)-P(2) bond length is 2.27 Å. The P(1)-Se(2) bond length is 2.18 Å. The P(1)-Se(3) bond length is 2.20 Å. The P(1)-Se(5) bond length is 2.31 Å. In the second P site, P(2) is bonded to one P(1), one Se(1), one Se(4), and one Se(5) atom to form distorted PPSe3 tetrahedra that share  a cornercorner with one P(1)PSe3 tetrahedra and corners with two equivalent Cu(1)Se4 tetrahedra. The P(2)-Se(1) bond length is 2.17 Å. The P(2)-Se(4) bond length is 2.22 Å. The P(2)-Se(5) bond length is 2.30 Å. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted see-saw-like geometry to three equivalent K(1) and one P(2) atom. In the second Se site, Se(2) is bonded in a 4-coordinate geometry to two equivalent K(1), one Cu(1), and one P(1) atom. In the third Se site, Se(3) is bonded in a 4-coordinate geometry to two equivalent K(1), one Cu(1), and one P(1) atom. In the fourth Se site, Se(4) is bonded to one K(1), two equivalent Cu(1), and one P(2) atom to form distorted SeKCu2P trigonal pyramids that share  a cornercorner with one P(1)PSe3 tetrahedra and corners with two equivalent Se(4)KCu2P trigonal pyramids. In the fifth Se site, Se(5) is bonded in a distorted water-like geometry to one K(1), one P(1), and one P(2) atom.