SrEu4Se5 is Caswellsilverite-like structured and crystallizes in the monoclinic C2/m space group. Sr(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form SrSe6 octahedra that share corners with two equivalent Eu(1)Se6 octahedra, corners with four equivalent Eu(2)Se6 octahedra, edges with two equivalent Sr(1)Se6 octahedra, edges with four equivalent Eu(1)Se6 octahedra, and edges with six equivalent Eu(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to one Se(2), two equivalent Se(3), and three equivalent Se(1) atoms to form EuSe6 octahedra that share  a cornercorner with one Sr(1)Se6 octahedra, corners with two equivalent Eu(1)Se6 octahedra, corners with three equivalent Eu(2)Se6 octahedra, edges with two equivalent Sr(1)Se6 octahedra, edges with five equivalent Eu(1)Se6 octahedra, and edges with five equivalent Eu(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the second Eu site, Eu(2) is bonded to one Se(3), two equivalent Se(1), and three equivalent Se(2) atoms to form EuSe6 octahedra that share  a cornercorner with one Eu(2)Se6 octahedra, corners with two equivalent Sr(1)Se6 octahedra, corners with three equivalent Eu(1)Se6 octahedra, edges with three equivalent Sr(1)Se6 octahedra, edges with four equivalent Eu(2)Se6 octahedra, and edges with five equivalent Eu(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Sr(1), two equivalent Eu(2), and three equivalent Eu(1) atoms to form SeSrEu5 octahedra that share  a cornercorner with one Se(1)SrEu5 octahedra, corners with two equivalent Se(3)Eu6 octahedra, corners with three equivalent Se(2)Sr2Eu4 octahedra, edges with three equivalent Se(3)Eu6 octahedra, edges with four equivalent Se(1)SrEu5 octahedra, and edges with five equivalent Se(2)Sr2Eu4 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the second Se site, Se(2) is bonded to two equivalent Sr(1), one Eu(1), and three equivalent Eu(2) atoms to form SeSr2Eu4 octahedra that share  a cornercorner with one Se(3)Eu6 octahedra, corners with two equivalent Se(2)Sr2Eu4 octahedra, corners with three equivalent Se(1)SrEu5 octahedra, edges with two equivalent Se(3)Eu6 octahedra, edges with five equivalent Se(2)Sr2Eu4 octahedra, and edges with five equivalent Se(1)SrEu5 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the third Se site, Se(3) is bonded to two equivalent Eu(2) and four equivalent Eu(1) atoms to form SeEu6 octahedra that share corners with two equivalent Se(2)Sr2Eu4 octahedra, corners with four equivalent Se(1)SrEu5 octahedra, edges with two equivalent Se(3)Eu6 octahedra, edges with four equivalent Se(2)Sr2Eu4 octahedra, and edges with six equivalent Se(1)SrEu5 octahedra. The corner-sharing octahedral tilt angles are 1°.
SrEu4Se5 is Caswellsilverite-like structured and crystallizes in the monoclinic C2/m space group. Sr(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form SrSe6 octahedra that share corners with two equivalent Eu(1)Se6 octahedra, corners with four equivalent Eu(2)Se6 octahedra, edges with two equivalent Sr(1)Se6 octahedra, edges with four equivalent Eu(1)Se6 octahedra, and edges with six equivalent Eu(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. Both Sr(1)-Se(1) bond lengths are 3.11 Å. All Sr(1)-Se(2) bond lengths are 3.11 Å. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to one Se(2), two equivalent Se(3), and three equivalent Se(1) atoms to form EuSe6 octahedra that share  a cornercorner with one Sr(1)Se6 octahedra, corners with two equivalent Eu(1)Se6 octahedra, corners with three equivalent Eu(2)Se6 octahedra, edges with two equivalent Sr(1)Se6 octahedra, edges with five equivalent Eu(1)Se6 octahedra, and edges with five equivalent Eu(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. The Eu(1)-Se(2) bond length is 3.08 Å. Both Eu(1)-Se(3) bond lengths are 3.08 Å. There is one shorter (3.06 Å) and two longer (3.08 Å) Eu(1)-Se(1) bond lengths. In the second Eu site, Eu(2) is bonded to one Se(3), two equivalent Se(1), and three equivalent Se(2) atoms to form EuSe6 octahedra that share  a cornercorner with one Eu(2)Se6 octahedra, corners with two equivalent Sr(1)Se6 octahedra, corners with three equivalent Eu(1)Se6 octahedra, edges with three equivalent Sr(1)Se6 octahedra, edges with four equivalent Eu(2)Se6 octahedra, and edges with five equivalent Eu(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. The Eu(2)-Se(3) bond length is 3.08 Å. Both Eu(2)-Se(1) bond lengths are 3.08 Å. There are two shorter (3.06 Å) and one longer (3.09 Å) Eu(2)-Se(2) bond length. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Sr(1), two equivalent Eu(2), and three equivalent Eu(1) atoms to form SeSrEu5 octahedra that share  a cornercorner with one Se(1)SrEu5 octahedra, corners with two equivalent Se(3)Eu6 octahedra, corners with three equivalent Se(2)Sr2Eu4 octahedra, edges with three equivalent Se(3)Eu6 octahedra, edges with four equivalent Se(1)SrEu5 octahedra, and edges with five equivalent Se(2)Sr2Eu4 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the second Se site, Se(2) is bonded to two equivalent Sr(1), one Eu(1), and three equivalent Eu(2) atoms to form SeSr2Eu4 octahedra that share  a cornercorner with one Se(3)Eu6 octahedra, corners with two equivalent Se(2)Sr2Eu4 octahedra, corners with three equivalent Se(1)SrEu5 octahedra, edges with two equivalent Se(3)Eu6 octahedra, edges with five equivalent Se(2)Sr2Eu4 octahedra, and edges with five equivalent Se(1)SrEu5 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the third Se site, Se(3) is bonded to two equivalent Eu(2) and four equivalent Eu(1) atoms to form SeEu6 octahedra that share corners with two equivalent Se(2)Sr2Eu4 octahedra, corners with four equivalent Se(1)SrEu5 octahedra, edges with two equivalent Se(3)Eu6 octahedra, edges with four equivalent Se(2)Sr2Eu4 octahedra, and edges with six equivalent Se(1)SrEu5 octahedra. The corner-sharing octahedral tilt angles are 1°.