K2GeSe4 crystallizes in the monoclinic P2_1/c 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(4), two equivalent Se(1), two equivalent Se(3), and three equivalent Se(2) atoms. In the second K site, K(2) is bonded in a 6-coordinate geometry to three equivalent Se(3) and three equivalent Se(4) atoms. Ge(1) is bonded in a distorted tetrahedral geometry to one Se(1), one Se(2), one Se(3), and one Se(4) atom. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a 1-coordinate geometry to two equivalent K(1), one Ge(1), and one Se(2) atom. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to three equivalent K(1), one Ge(1), and one Se(1) atom. In the third Se site, Se(3) is bonded to two equivalent K(1), three equivalent K(2), and one Ge(1) atom to form distorted SeK5Ge octahedra that share corners with two equivalent Se(3)K5Ge octahedra, corners with two equivalent Se(4)K4Ge trigonal bipyramids, edges with three equivalent Se(3)K5Ge octahedra, and edges with five equivalent Se(4)K4Ge trigonal bipyramids. The corner-sharing octahedral tilt angles are 26°. In the fourth Se site, Se(4) is bonded to one K(1), three equivalent K(2), and one Ge(1) atom to form distorted SeK4Ge trigonal bipyramids that share corners with two equivalent Se(3)K5Ge octahedra, corners with four equivalent Se(4)K4Ge trigonal bipyramids, edges with five equivalent Se(3)K5Ge octahedra, and  an edgeedge with one Se(4)K4Ge trigonal bipyramid. The corner-sharing octahedral tilt angles range from 21-56°.
K2GeSe4 crystallizes in the monoclinic P2_1/c 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(4), two equivalent Se(1), two equivalent Se(3), and three equivalent Se(2) atoms. The K(1)-Se(4) bond length is 3.39 Å. There is one shorter (3.55 Å) and one longer (3.71 Å) K(1)-Se(1) bond length. There is one shorter (3.32 Å) and one longer (3.39 Å) K(1)-Se(3) bond length. There are a spread of K(1)-Se(2) bond distances ranging from 3.41-3.79 Å. In the second K site, K(2) is bonded in a 6-coordinate geometry to three equivalent Se(3) and three equivalent Se(4) atoms. There are a spread of K(2)-Se(3) bond distances ranging from 3.41-3.46 Å. There is one shorter (3.36 Å) and two longer (3.43 Å) K(2)-Se(4) bond lengths. Ge(1) is bonded in a distorted tetrahedral geometry to one Se(1), one Se(2), one Se(3), and one Se(4) atom. The Ge(1)-Se(1) bond length is 2.44 Å. The Ge(1)-Se(2) bond length is 2.45 Å. The Ge(1)-Se(3) bond length is 2.31 Å. The Ge(1)-Se(4) bond length is 2.27 Å. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a 1-coordinate geometry to two equivalent K(1), one Ge(1), and one Se(2) atom. The Se(1)-Se(2) bond length is 2.35 Å. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to three equivalent K(1), one Ge(1), and one Se(1) atom. In the third Se site, Se(3) is bonded to two equivalent K(1), three equivalent K(2), and one Ge(1) atom to form distorted SeK5Ge octahedra that share corners with two equivalent Se(3)K5Ge octahedra, corners with two equivalent Se(4)K4Ge trigonal bipyramids, edges with three equivalent Se(3)K5Ge octahedra, and edges with five equivalent Se(4)K4Ge trigonal bipyramids. The corner-sharing octahedral tilt angles are 26°. In the fourth Se site, Se(4) is bonded to one K(1), three equivalent K(2), and one Ge(1) atom to form distorted SeK4Ge trigonal bipyramids that share corners with two equivalent Se(3)K5Ge octahedra, corners with four equivalent Se(4)K4Ge trigonal bipyramids, edges with five equivalent Se(3)K5Ge octahedra, and  an edgeedge with one Se(4)K4Ge trigonal bipyramid. The corner-sharing octahedral tilt angles range from 21-56°.