LaYbSe3 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 68°. La(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 La(1) atoms to form SeLa2Yb2 tetrahedra that share corners with eight equivalent Se(2)La3Yb2 square pyramids, corners with four equivalent Se(1)La2Yb2 tetrahedra, and edges with six equivalent Se(2)La3Yb2 square pyramids. In the second Se site, Se(2) is bonded to two equivalent Yb(1) and three equivalent La(1) atoms to form distorted SeLa3Yb2 square pyramids that share corners with nine equivalent Se(2)La3Yb2 square pyramids, corners with four equivalent Se(1)La2Yb2 tetrahedra, edges with six equivalent Se(2)La3Yb2 square pyramids, and edges with three equivalent Se(1)La2Yb2 tetrahedra.
LaYbSe3 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 68°. Both Yb(1)-Se(1) bond lengths are 2.81 Å. All Yb(1)-Se(2) bond lengths are 3.01 Å. La(1) is bonded in a 8-coordinate geometry to two equivalent Se(1) and six equivalent Se(2) atoms. Both La(1)-Se(1) bond lengths are 2.94 Å. There are four shorter (3.10 Å) and two longer (3.45 Å) La(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 La(1) atoms to form SeLa2Yb2 tetrahedra that share corners with eight equivalent Se(2)La3Yb2 square pyramids, corners with four equivalent Se(1)La2Yb2 tetrahedra, and edges with six equivalent Se(2)La3Yb2 square pyramids. In the second Se site, Se(2) is bonded to two equivalent Yb(1) and three equivalent La(1) atoms to form distorted SeLa3Yb2 square pyramids that share corners with nine equivalent Se(2)La3Yb2 square pyramids, corners with four equivalent Se(1)La2Yb2 tetrahedra, edges with six equivalent Se(2)La3Yb2 square pyramids, and edges with three equivalent Se(1)La2Yb2 tetrahedra.