NdYbSe3 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 edge and corner-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles are 69°. Nd(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 Nd(1) atoms to form SeYb2Nd2 tetrahedra that share corners with eight equivalent Se(2)Yb2Nd3 square pyramids, corners with four equivalent Se(1)Yb2Nd2 tetrahedra, and edges with six equivalent Se(2)Yb2Nd3 square pyramids. In the second Se site, Se(2) is bonded to two equivalent Yb(1) and three equivalent Nd(1) atoms to form distorted SeYb2Nd3 square pyramids that share corners with nine equivalent Se(2)Yb2Nd3 square pyramids, corners with four equivalent Se(1)Yb2Nd2 tetrahedra, edges with six equivalent Se(2)Yb2Nd3 square pyramids, and edges with three equivalent Se(1)Yb2Nd2 tetrahedra.
NdYbSe3 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 edge and corner-sharing YbSe6 octahedra. The corner-sharing octahedral tilt angles are 69°. Both Yb(1)-Se(1) bond lengths are 2.81 Å. All Yb(1)-Se(2) bond lengths are 2.99 Å. Nd(1) is bonded in a 8-coordinate geometry to two equivalent Se(1) and six equivalent Se(2) atoms. Both Nd(1)-Se(1) bond lengths are 2.91 Å. There are four shorter (3.05 Å) and two longer (3.42 Å) Nd(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 Nd(1) atoms to form SeYb2Nd2 tetrahedra that share corners with eight equivalent Se(2)Yb2Nd3 square pyramids, corners with four equivalent Se(1)Yb2Nd2 tetrahedra, and edges with six equivalent Se(2)Yb2Nd3 square pyramids. In the second Se site, Se(2) is bonded to two equivalent Yb(1) and three equivalent Nd(1) atoms to form distorted SeYb2Nd3 square pyramids that share corners with nine equivalent Se(2)Yb2Nd3 square pyramids, corners with four equivalent Se(1)Yb2Nd2 tetrahedra, edges with six equivalent Se(2)Yb2Nd3 square pyramids, and edges with three equivalent Se(1)Yb2Nd2 tetrahedra.