FeSe2 is Marcasite structured and crystallizes in the orthorhombic Pnnm space group. Fe(1) is bonded to six equivalent Se(1) atoms to form a mixture of corner and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles are 58°. Se(1) is bonded in a 3-coordinate geometry to three equivalent Fe(1) atoms.
FeSe2 is Marcasite structured and crystallizes in the orthorhombic Pnnm space group. Fe(1) is bonded to six equivalent Se(1) atoms to form a mixture of corner and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles are 58°. There are two shorter (2.36 Å) and four longer (2.38 Å) Fe(1)-Se(1) bond lengths. Se(1) is bonded in a 3-coordinate geometry to three equivalent Fe(1) atoms.