Tb3CuSe6 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), two equivalent Se(4), and two equivalent Se(5) atoms. In the second Tb site, Tb(2) is bonded in a 9-coordinate geometry to one Cu(1), one Se(1), one Se(3), one Se(4), one Se(5), two equivalent Se(2), and two equivalent Se(6) atoms. In the third Tb site, Tb(3) is bonded in a 10-coordinate geometry to two equivalent Cu(1), one Se(2), one Se(3), one Se(4), one Se(5), two equivalent Se(1), and two equivalent Se(6) atoms. Cu(1) is bonded in a 4-coordinate geometry to one Tb(2), two equivalent Tb(3), one Se(2), one Se(6), and two equivalent Se(1) atoms. There are six inequivalent Se sites. In the first Se site, Se(6) is bonded in a 5-coordinate geometry to two equivalent Tb(2), two equivalent Tb(3), one Cu(1), and one Se(5) atom. In the second Se site, Se(1) is bonded in a 6-coordinate geometry to one Tb(1), one Tb(2), two equivalent Tb(3), and two equivalent Cu(1) atoms. In the third Se site, Se(2) is bonded in a 5-coordinate geometry to one Tb(1), one Tb(3), two equivalent Tb(2), and one Cu(1) atom. In the fourth Se site, Se(3) is bonded to one Tb(2), one Tb(3), and two equivalent Tb(1) atoms to form distorted corner-sharing SeTb4 trigonal pyramids. In the fifth Se site, Se(4) is bonded in a 5-coordinate geometry to one Tb(2), one Tb(3), two equivalent Tb(1), and one Se(5) atom. In the sixth Se site, Se(5) is bonded in a 6-coordinate geometry to one Tb(2), one Tb(3), two equivalent Tb(1), one Se(4), and one Se(6) atom.
Tb3CuSe6 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), two equivalent Se(4), and two equivalent Se(5) atoms. The Tb(1)-Se(1) bond length is 3.02 Å. The Tb(1)-Se(2) bond length is 3.01 Å. Both Tb(1)-Se(3) bond lengths are 2.79 Å. There is one shorter (3.02 Å) and one longer (3.09 Å) Tb(1)-Se(4) bond length. There is one shorter (3.03 Å) and one longer (3.11 Å) Tb(1)-Se(5) bond length. In the second Tb site, Tb(2) is bonded in a 9-coordinate geometry to one Cu(1), one Se(1), one Se(3), one Se(4), one Se(5), two equivalent Se(2), and two equivalent Se(6) atoms. The Tb(2)-Cu(1) bond length is 3.10 Å. The Tb(2)-Se(1) bond length is 2.94 Å. The Tb(2)-Se(3) bond length is 2.96 Å. The Tb(2)-Se(4) bond length is 3.07 Å. The Tb(2)-Se(5) bond length is 3.08 Å. There is one shorter (2.94 Å) and one longer (3.08 Å) Tb(2)-Se(2) bond length. There is one shorter (3.02 Å) and one longer (3.10 Å) Tb(2)-Se(6) bond length. In the third Tb site, Tb(3) is bonded in a 10-coordinate geometry to two equivalent Cu(1), one Se(2), one Se(3), one Se(4), one Se(5), two equivalent Se(1), and two equivalent Se(6) atoms. There is one shorter (3.12 Å) and one longer (3.13 Å) Tb(3)-Cu(1) bond length. The Tb(3)-Se(2) bond length is 2.93 Å. The Tb(3)-Se(3) bond length is 2.94 Å. The Tb(3)-Se(4) bond length is 3.07 Å. The Tb(3)-Se(5) bond length is 3.04 Å. There is one shorter (2.93 Å) and one longer (3.18 Å) Tb(3)-Se(1) bond length. There is one shorter (3.02 Å) and one longer (3.09 Å) Tb(3)-Se(6) bond length. Cu(1) is bonded in a 4-coordinate geometry to one Tb(2), two equivalent Tb(3), one Se(2), one Se(6), and two equivalent Se(1) atoms. The Cu(1)-Se(2) bond length is 2.40 Å. The Cu(1)-Se(6) bond length is 2.42 Å. There is one shorter (2.53 Å) and one longer (2.58 Å) Cu(1)-Se(1) bond length. There are six inequivalent Se sites. In the first Se site, Se(6) is bonded in a 5-coordinate geometry to two equivalent Tb(2), two equivalent Tb(3), one Cu(1), and one Se(5) atom. The Se(6)-Se(5) bond length is 3.02 Å. In the second Se site, Se(1) is bonded in a 6-coordinate geometry to one Tb(1), one Tb(2), two equivalent Tb(3), and two equivalent Cu(1) atoms. In the third Se site, Se(2) is bonded in a 5-coordinate geometry to one Tb(1), one Tb(3), two equivalent Tb(2), and one Cu(1) atom. In the fourth Se site, Se(3) is bonded to one Tb(2), one Tb(3), and two equivalent Tb(1) atoms to form distorted corner-sharing SeTb4 trigonal pyramids. In the fifth Se site, Se(4) is bonded in a 5-coordinate geometry to one Tb(2), one Tb(3), two equivalent Tb(1), and one Se(5) atom. The Se(4)-Se(5) bond length is 2.46 Å. In the sixth Se site, Se(5) is bonded in a 6-coordinate geometry to one Tb(2), one Tb(3), two equivalent Tb(1), one Se(4), and one Se(6) atom.