K3(FeSe2)2 crystallizes in the orthorhombic Pnma space group. There are two inequivalent K sites. In the first K site, K(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form KSe6 octahedra that share corners with eight equivalent Fe(1)Se4 tetrahedra, edges with two equivalent Fe(1)Se4 tetrahedra, and faces with two equivalent K(1)Se6 octahedra. In the second K site, K(2) is bonded in a 6-coordinate geometry to one Se(2), two equivalent Se(3), and three equivalent Se(1) atoms. Fe(1) is bonded to one Se(2), one Se(3), and two equivalent Se(1) atoms to form FeSe4 tetrahedra that share corners with four equivalent K(1)Se6 octahedra,  an edgeedge with one K(1)Se6 octahedra, and edges with two equivalent Fe(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 20-63°. There are three inequivalent Se sites. In the first Se site, Se(3) is bonded in a 6-coordinate geometry to four equivalent K(2) and two equivalent Fe(1) atoms. In the second Se site, Se(1) is bonded in a 7-coordinate geometry to two equivalent K(1), three equivalent K(2), and two equivalent Fe(1) atoms. In the third Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent K(1), two equivalent K(2), and two equivalent Fe(1) atoms.
K3(FeSe2)2 crystallizes in the orthorhombic Pnma space group. There are two inequivalent K sites. In the first K site, K(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form KSe6 octahedra that share corners with eight equivalent Fe(1)Se4 tetrahedra, edges with two equivalent Fe(1)Se4 tetrahedra, and faces with two equivalent K(1)Se6 octahedra. There is one shorter (3.23 Å) and one longer (3.24 Å) K(1)-Se(2) bond length. There are two shorter (3.28 Å) and two longer (3.41 Å) K(1)-Se(1) bond lengths. In the second K site, K(2) is bonded in a 6-coordinate geometry to one Se(2), two equivalent Se(3), and three equivalent Se(1) atoms. The K(2)-Se(2) bond length is 3.53 Å. There is one shorter (3.25 Å) and one longer (3.33 Å) K(2)-Se(3) bond length. There are a spread of K(2)-Se(1) bond distances ranging from 3.45-3.59 Å. Fe(1) is bonded to one Se(2), one Se(3), and two equivalent Se(1) atoms to form FeSe4 tetrahedra that share corners with four equivalent K(1)Se6 octahedra,  an edgeedge with one K(1)Se6 octahedra, and edges with two equivalent Fe(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 20-63°. The Fe(1)-Se(2) bond length is 2.45 Å. The Fe(1)-Se(3) bond length is 2.41 Å. There is one shorter (2.46 Å) and one longer (2.49 Å) Fe(1)-Se(1) bond length. There are three inequivalent Se sites. In the first Se site, Se(3) is bonded in a 6-coordinate geometry to four equivalent K(2) and two equivalent Fe(1) atoms. In the second Se site, Se(1) is bonded in a 7-coordinate geometry to two equivalent K(1), three equivalent K(2), and two equivalent Fe(1) atoms. In the third Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent K(1), two equivalent K(2), and two equivalent Fe(1) atoms.