KEuPSe4 crystallizes in the orthorhombic Pnma space group. K(1) is bonded in a 8-coordinate geometry to one Se(3), three equivalent Se(1), and four equivalent Se(2) atoms. Eu(1) is bonded in a 8-coordinate geometry to one Se(1), three equivalent Se(3), and four equivalent Se(2) atoms. P(1) is bonded in a tetrahedral geometry to one Se(1), one Se(3), and two equivalent Se(2) atoms. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent K(1), one Eu(1), and one P(1) atom to form distorted SeK3EuP trigonal bipyramids that share corners with six equivalent Se(2)K2Eu2P square pyramids, corners with six equivalent Se(1)K3EuP trigonal bipyramids, and edges with six equivalent Se(2)K2Eu2P square pyramids. In the second Se site, Se(2) is bonded to two equivalent K(1), two equivalent Eu(1), and one P(1) atom to form distorted SeK2Eu2P square pyramids that share corners with six equivalent Se(2)K2Eu2P square pyramids, corners with three equivalent Se(1)K3EuP trigonal bipyramids, edges with two equivalent Se(2)K2Eu2P square pyramids, edges with three equivalent Se(1)K3EuP trigonal bipyramids, and  a faceface with one Se(2)K2Eu2P square pyramid. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to one K(1), three equivalent Eu(1), and one P(1) atom.
KEuPSe4 crystallizes in the orthorhombic Pnma space group. K(1) is bonded in a 8-coordinate geometry to one Se(3), three equivalent Se(1), and four equivalent Se(2) atoms. The K(1)-Se(3) bond length is 3.44 Å. All K(1)-Se(1) bond lengths are 3.58 Å. There are two shorter (3.52 Å) and two longer (3.53 Å) K(1)-Se(2) bond lengths. Eu(1) is bonded in a 8-coordinate geometry to one Se(1), three equivalent Se(3), and four equivalent Se(2) atoms. The Eu(1)-Se(1) bond length is 3.08 Å. There is one shorter (3.10 Å) and two longer (3.61 Å) Eu(1)-Se(3) bond lengths. There are two shorter (3.11 Å) and two longer (3.16 Å) Eu(1)-Se(2) bond lengths. P(1) is bonded in a tetrahedral geometry to one Se(1), one Se(3), and two equivalent Se(2) atoms. The P(1)-Se(1) bond length is 2.19 Å. The P(1)-Se(3) bond length is 2.21 Å. Both P(1)-Se(2) bond lengths are 2.21 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent K(1), one Eu(1), and one P(1) atom to form distorted SeK3EuP trigonal bipyramids that share corners with six equivalent Se(2)K2Eu2P square pyramids, corners with six equivalent Se(1)K3EuP trigonal bipyramids, and edges with six equivalent Se(2)K2Eu2P square pyramids. In the second Se site, Se(2) is bonded to two equivalent K(1), two equivalent Eu(1), and one P(1) atom to form distorted SeK2Eu2P square pyramids that share corners with six equivalent Se(2)K2Eu2P square pyramids, corners with three equivalent Se(1)K3EuP trigonal bipyramids, edges with two equivalent Se(2)K2Eu2P square pyramids, edges with three equivalent Se(1)K3EuP trigonal bipyramids, and  a faceface with one Se(2)K2Eu2P square pyramid. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to one K(1), three equivalent Eu(1), and one P(1) atom.