ErTl(PSe3)2 is Zircon-derived structured and crystallizes in the monoclinic P2_1 space group. Er(1) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), two equivalent Se(5), and two equivalent Se(6) atoms. Tl(1) is bonded in a 5-coordinate geometry to one Se(1), two equivalent Se(2), and two equivalent Se(4) atoms. There are two inequivalent P sites. In the first P site, P(1) is bonded in a distorted tetrahedral geometry to one P(2), one Se(1), one Se(3), and one Se(6) atom. In the second P site, P(2) is bonded in a distorted tetrahedral geometry to one P(1), one Se(2), one Se(4), and one Se(5) atom. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted L-shaped geometry to one Er(1), one Tl(1), and one P(1) atom. In the second Se site, Se(2) is bonded in a 2-coordinate geometry to one Er(1), two equivalent Tl(1), and one P(2) atom. In the third Se site, Se(3) is bonded in a trigonal non-coplanar geometry to two equivalent Er(1) and one P(1) atom. In the fourth Se site, Se(4) is bonded in a 3-coordinate geometry to two equivalent Tl(1) and one P(2) atom. In the fifth Se site, Se(5) is bonded in a trigonal non-coplanar geometry to two equivalent Er(1) and one P(2) atom. In the sixth Se site, Se(6) is bonded in a distorted T-shaped geometry to two equivalent Er(1) and one P(1) atom.
ErTl(PSe3)2 is Zircon-derived structured and crystallizes in the monoclinic P2_1 space group. Er(1) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), two equivalent Se(5), and two equivalent Se(6) atoms. The Er(1)-Se(1) bond length is 3.05 Å. The Er(1)-Se(2) bond length is 3.02 Å. There is one shorter (2.99 Å) and one longer (3.09 Å) Er(1)-Se(3) bond length. There is one shorter (3.00 Å) and one longer (3.11 Å) Er(1)-Se(5) bond length. There is one shorter (2.96 Å) and one longer (3.00 Å) Er(1)-Se(6) bond length. Tl(1) is bonded in a 5-coordinate geometry to one Se(1), two equivalent Se(2), and two equivalent Se(4) atoms. The Tl(1)-Se(1) bond length is 3.44 Å. There is one shorter (3.34 Å) and one longer (3.43 Å) Tl(1)-Se(2) bond length. There is one shorter (3.27 Å) and one longer (3.36 Å) Tl(1)-Se(4) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded in a distorted tetrahedral geometry to one P(2), one Se(1), one Se(3), and one Se(6) atom. The P(1)-P(2) bond length is 2.26 Å. The P(1)-Se(1) bond length is 2.20 Å. The P(1)-Se(3) bond length is 2.23 Å. The P(1)-Se(6) bond length is 2.25 Å. In the second P site, P(2) is bonded in a distorted tetrahedral geometry to one P(1), one Se(2), one Se(4), and one Se(5) atom. The P(2)-Se(2) bond length is 2.19 Å. The P(2)-Se(4) bond length is 2.17 Å. The P(2)-Se(5) bond length is 2.25 Å. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted L-shaped geometry to one Er(1), one Tl(1), and one P(1) atom. In the second Se site, Se(2) is bonded in a 2-coordinate geometry to one Er(1), two equivalent Tl(1), and one P(2) atom. In the third Se site, Se(3) is bonded in a trigonal non-coplanar geometry to two equivalent Er(1) and one P(1) atom. In the fourth Se site, Se(4) is bonded in a 3-coordinate geometry to two equivalent Tl(1) and one P(2) atom. In the fifth Se site, Se(5) is bonded in a trigonal non-coplanar geometry to two equivalent Er(1) and one P(2) atom. In the sixth Se site, Se(6) is bonded in a distorted T-shaped geometry to two equivalent Er(1) and one P(1) atom.