Tb2Se3 is Stibnite structured and crystallizes in the orthorhombic Pnma space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to two equivalent Se(1), two equivalent Se(2), and three equivalent Se(3) atoms to form a mixture of distorted edge and corner-sharing TbSe7 pentagonal bipyramids. In the second Tb site, Tb(2) is bonded in a 8-coordinate geometry to two equivalent Se(3), three equivalent Se(1), and three equivalent Se(2) atoms. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to two equivalent Tb(1) and three equivalent Tb(2) atoms. In the second Se site, Se(2) is bonded to two equivalent Tb(1) and three equivalent Tb(2) atoms to form a mixture of distorted edge and corner-sharing SeTb5 trigonal bipyramids. In the third Se site, Se(3) is bonded to two equivalent Tb(2) and three equivalent Tb(1) atoms to form a mixture of edge and corner-sharing SeTb5 square pyramids.
Tb2Se3 is Stibnite structured and crystallizes in the orthorhombic Pnma space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to two equivalent Se(1), two equivalent Se(2), and three equivalent Se(3) atoms to form a mixture of distorted edge and corner-sharing TbSe7 pentagonal bipyramids. There is one shorter (2.92 Å) and one longer (2.96 Å) Tb(1)-Se(1) bond length. Both Tb(1)-Se(2) bond lengths are 2.90 Å. There are two shorter (2.88 Å) and one longer (2.93 Å) Tb(1)-Se(3) bond length. In the second Tb site, Tb(2) is bonded in a 8-coordinate geometry to two equivalent Se(3), three equivalent Se(1), and three equivalent Se(2) atoms. Both Tb(2)-Se(3) bond lengths are 2.98 Å. There are two shorter (2.95 Å) and one longer (3.50 Å) Tb(2)-Se(1) bond length. There are two shorter (2.96 Å) and one longer (2.99 Å) Tb(2)-Se(2) bond length. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to two equivalent Tb(1) and three equivalent Tb(2) atoms. In the second Se site, Se(2) is bonded to two equivalent Tb(1) and three equivalent Tb(2) atoms to form a mixture of distorted edge and corner-sharing SeTb5 trigonal bipyramids. In the third Se site, Se(3) is bonded to two equivalent Tb(2) and three equivalent Tb(1) atoms to form a mixture of edge and corner-sharing SeTb5 square pyramids.