K4Eu(PSe4)2 crystallizes in the orthorhombic Ibam space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to one Se(2), one Se(3), and six equivalent Se(1) atoms. In the second K site, K(2) is bonded in a 6-coordinate geometry to two equivalent Se(2) and four equivalent Se(3) atoms. Eu(1) is bonded to four equivalent Se(1) and four equivalent Se(2) atoms to form distorted EuSe8 hexagonal bipyramids that share edges with two equivalent Eu(1)Se8 hexagonal bipyramids and edges with four equivalent P(1)Se4 tetrahedra. P(1) is bonded to one Se(2), one Se(3), and two equivalent Se(1) atoms to form PSe4 tetrahedra that share edges with two equivalent Eu(1)Se8 hexagonal bipyramids. There are three inequivalent Se sites. In the first Se site, Se(2) is bonded in a 6-coordinate geometry to one K(1), two equivalent K(2), two equivalent Eu(1), and one P(1) atom. In the second Se site, Se(3) is bonded to one K(1), four equivalent K(2), and one P(1) atom to form a mixture of distorted corner and edge-sharing SeK5P octahedra. The corner-sharing octahedral tilt angles range from 1-11°. In the third Se site, Se(1) is bonded in a 5-coordinate geometry to three equivalent K(1), one Eu(1), and one P(1) atom.
K4Eu(PSe4)2 crystallizes in the orthorhombic Ibam space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to one Se(2), one Se(3), and six equivalent Se(1) atoms. The K(1)-Se(2) bond length is 3.27 Å. The K(1)-Se(3) bond length is 3.58 Å. There are a spread of K(1)-Se(1) bond distances ranging from 3.45-3.67 Å. In the second K site, K(2) is bonded in a 6-coordinate geometry to two equivalent Se(2) and four equivalent Se(3) atoms. Both K(2)-Se(2) bond lengths are 3.69 Å. There are two shorter (3.46 Å) and two longer (3.49 Å) K(2)-Se(3) bond lengths. Eu(1) is bonded to four equivalent Se(1) and four equivalent Se(2) atoms to form distorted EuSe8 hexagonal bipyramids that share edges with two equivalent Eu(1)Se8 hexagonal bipyramids and edges with four equivalent P(1)Se4 tetrahedra. All Eu(1)-Se(1) bond lengths are 3.24 Å. All Eu(1)-Se(2) bond lengths are 3.29 Å. P(1) is bonded to one Se(2), one Se(3), and two equivalent Se(1) atoms to form PSe4 tetrahedra that share edges with two equivalent Eu(1)Se8 hexagonal bipyramids. The P(1)-Se(2) bond length is 2.25 Å. The P(1)-Se(3) bond length is 2.22 Å. Both P(1)-Se(1) bond lengths are 2.24 Å. There are three inequivalent Se sites. In the first Se site, Se(2) is bonded in a 6-coordinate geometry to one K(1), two equivalent K(2), two equivalent Eu(1), and one P(1) atom. In the second Se site, Se(3) is bonded to one K(1), four equivalent K(2), and one P(1) atom to form a mixture of distorted corner and edge-sharing SeK5P octahedra. The corner-sharing octahedral tilt angles range from 1-11°. In the third Se site, Se(1) is bonded in a 5-coordinate geometry to three equivalent K(1), one Eu(1), and one P(1) atom.