EuYb2Se4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Yb sites. In the first Yb site, Yb(1) is bonded to one Se(1), two equivalent Se(4), and three equivalent Se(3) atoms to form a mixture of corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-72°. In the second Yb site, Yb(2) is bonded to one Se(4), two equivalent Se(1), and three equivalent Se(2) atoms to form a mixture of corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-72°. Eu(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to one Yb(1), two equivalent Yb(2), and two equivalent Eu(1) atoms to form a mixture of distorted corner and edge-sharing SeYb3Eu2 trigonal bipyramids. In the second Se site, Se(2) is bonded to three equivalent Yb(2) and two equivalent Eu(1) atoms to form a mixture of distorted corner and edge-sharing SeYb3Eu2 trigonal bipyramids. In the third Se site, Se(3) is bonded to three equivalent Yb(1) and two equivalent Eu(1) atoms to form a mixture of corner and edge-sharing SeYb3Eu2 square pyramids. In the fourth Se site, Se(4) is bonded to one Yb(2), two equivalent Yb(1), and two equivalent Eu(1) atoms to form a mixture of distorted corner and edge-sharing SeYb3Eu2 trigonal bipyramids.
EuYb2Se4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Yb sites. In the first Yb site, Yb(1) is bonded to one Se(1), two equivalent Se(4), and three equivalent Se(3) atoms to form a mixture of corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-72°. The Yb(1)-Se(1) bond length is 2.86 Å. Both Yb(1)-Se(4) bond lengths are 2.91 Å. There is one shorter (2.93 Å) and two longer (3.02 Å) Yb(1)-Se(3) bond lengths. In the second Yb site, Yb(2) is bonded to one Se(4), two equivalent Se(1), and three equivalent Se(2) atoms to form a mixture of corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-72°. The Yb(2)-Se(4) bond length is 2.89 Å. Both Yb(2)-Se(1) bond lengths are 2.95 Å. All Yb(2)-Se(2) bond lengths are 3.00 Å. Eu(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. Both Eu(1)-Se(1) bond lengths are 3.09 Å. Both Eu(1)-Se(2) bond lengths are 3.11 Å. Both Eu(1)-Se(3) bond lengths are 3.16 Å. There is one shorter (3.29 Å) and one longer (3.34 Å) Eu(1)-Se(4) bond length. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to one Yb(1), two equivalent Yb(2), and two equivalent Eu(1) atoms to form a mixture of distorted corner and edge-sharing SeYb3Eu2 trigonal bipyramids. In the second Se site, Se(2) is bonded to three equivalent Yb(2) and two equivalent Eu(1) atoms to form a mixture of distorted corner and edge-sharing SeYb3Eu2 trigonal bipyramids. In the third Se site, Se(3) is bonded to three equivalent Yb(1) and two equivalent Eu(1) atoms to form a mixture of corner and edge-sharing SeYb3Eu2 square pyramids. In the fourth Se site, Se(4) is bonded to one Yb(2), two equivalent Yb(1), and two equivalent Eu(1) atoms to form a mixture of distorted corner and edge-sharing SeYb3Eu2 trigonal bipyramids.