CeYbSe3 crystallizes in the orthorhombic Cmcm space group. Yb(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form a mixture of corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles are 63°. Ce(1) is bonded in a 8-coordinate geometry to two equivalent Se(1) and six equivalent Se(2) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Yb(1) and two equivalent Ce(1) atoms to form SeYb2Ce2 tetrahedra that share corners with four equivalent Se(1)Yb2Ce2 tetrahedra, corners with eight equivalent Se(2)Yb2Ce3 trigonal bipyramids, and edges with six equivalent Se(2)Yb2Ce3 trigonal bipyramids. In the second Se site, Se(2) is bonded to two equivalent Yb(1) and three equivalent Ce(1) atoms to form distorted SeYb2Ce3 trigonal bipyramids that share corners with four equivalent Se(1)Yb2Ce2 tetrahedra, corners with nine equivalent Se(2)Yb2Ce3 trigonal bipyramids, edges with three equivalent Se(1)Yb2Ce2 tetrahedra, and edges with six equivalent Se(2)Yb2Ce3 trigonal bipyramids.
CeYbSe3 crystallizes in the orthorhombic Cmcm space group. Yb(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form a mixture of corner and edge-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles are 63°. Both Yb(1)-Se(1) bond lengths are 2.83 Å. All Yb(1)-Se(2) bond lengths are 2.97 Å. Ce(1) is bonded in a 8-coordinate geometry to two equivalent Se(1) and six equivalent Se(2) atoms. Both Ce(1)-Se(1) bond lengths are 2.85 Å. There are four shorter (3.00 Å) and two longer (3.40 Å) Ce(1)-Se(2) bond lengths. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Yb(1) and two equivalent Ce(1) atoms to form SeYb2Ce2 tetrahedra that share corners with four equivalent Se(1)Yb2Ce2 tetrahedra, corners with eight equivalent Se(2)Yb2Ce3 trigonal bipyramids, and edges with six equivalent Se(2)Yb2Ce3 trigonal bipyramids. In the second Se site, Se(2) is bonded to two equivalent Yb(1) and three equivalent Ce(1) atoms to form distorted SeYb2Ce3 trigonal bipyramids that share corners with four equivalent Se(1)Yb2Ce2 tetrahedra, corners with nine equivalent Se(2)Yb2Ce3 trigonal bipyramids, edges with three equivalent Se(1)Yb2Ce2 tetrahedra, and edges with six equivalent Se(2)Yb2Ce3 trigonal bipyramids.