Zr4FeSe8 crystallizes in the monoclinic C2/m space group. There are two inequivalent Zr sites. In the first Zr site, Zr(1) is bonded to one Se(1), one Se(2), and four equivalent Se(3) atoms to form ZrSe6 octahedra that share corners with two equivalent Fe(1)Se6 octahedra, edges with two equivalent Zr(1)Se6 octahedra, edges with four equivalent Zr(2)Se6 octahedra, and  a faceface with one Fe(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 48°. In the second Zr site, Zr(2) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form ZrSe6 octahedra that share corners with four equivalent Fe(1)Se6 octahedra, edges with two equivalent Zr(2)Se6 octahedra, and edges with four equivalent Zr(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 48-49°. Fe(1) is bonded to two equivalent Se(1) and four equivalent Se(3) atoms to form FeSe6 octahedra that share corners with four equivalent Zr(1)Se6 octahedra, corners with eight equivalent Zr(2)Se6 octahedra, and faces with two equivalent Zr(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 48-49°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one Zr(1), two equivalent Zr(2), and one Fe(1) atom. In the second Se site, Se(2) is bonded in a distorted T-shaped geometry to one Zr(1) and two equivalent Zr(2) atoms. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Zr(2), two equivalent Zr(1), and one Fe(1) atom.
Zr4FeSe8 crystallizes in the monoclinic C2/m space group. There are two inequivalent Zr sites. In the first Zr site, Zr(1) is bonded to one Se(1), one Se(2), and four equivalent Se(3) atoms to form ZrSe6 octahedra that share corners with two equivalent Fe(1)Se6 octahedra, edges with two equivalent Zr(1)Se6 octahedra, edges with four equivalent Zr(2)Se6 octahedra, and  a faceface with one Fe(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 48°. The Zr(1)-Se(1) bond length is 2.72 Å. The Zr(1)-Se(2) bond length is 2.69 Å. There are two shorter (2.70 Å) and two longer (2.76 Å) Zr(1)-Se(3) bond lengths. In the second Zr site, Zr(2) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form ZrSe6 octahedra that share corners with four equivalent Fe(1)Se6 octahedra, edges with two equivalent Zr(2)Se6 octahedra, and edges with four equivalent Zr(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 48-49°. Both Zr(2)-Se(1) bond lengths are 2.75 Å. Both Zr(2)-Se(2) bond lengths are 2.68 Å. Both Zr(2)-Se(3) bond lengths are 2.74 Å. Fe(1) is bonded to two equivalent Se(1) and four equivalent Se(3) atoms to form FeSe6 octahedra that share corners with four equivalent Zr(1)Se6 octahedra, corners with eight equivalent Zr(2)Se6 octahedra, and faces with two equivalent Zr(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 48-49°. Both Fe(1)-Se(1) bond lengths are 2.65 Å. All Fe(1)-Se(3) bond lengths are 2.62 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one Zr(1), two equivalent Zr(2), and one Fe(1) atom. In the second Se site, Se(2) is bonded in a distorted T-shaped geometry to one Zr(1) and two equivalent Zr(2) atoms. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Zr(2), two equivalent Zr(1), and one Fe(1) atom.