Nb2Tl4Se11 crystallizes in the triclinic P-1 space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one Se(1), one Se(10), one Se(11), one Se(3), one Se(6), one Se(7), and one Se(9) atom to form distorted face-sharing NbSe7 pentagonal bipyramids. In the second Nb site, Nb(2) is bonded to one Se(10), one Se(2), one Se(3), one Se(4), one Se(5), one Se(6), and one Se(8) atom to form distorted face-sharing NbSe7 pentagonal bipyramids. There are four inequivalent Tl sites. In the first Tl site, Tl(1) is bonded in a 4-coordinate geometry to one Se(2), one Se(4), and two equivalent Se(8) atoms. In the second Tl site, Tl(2) is bonded in a 4-coordinate geometry to one Se(1), one Se(7), and two equivalent Se(11) atoms. In the third Tl site, Tl(3) is bonded in a 5-coordinate geometry to one Se(10), one Se(2), one Se(3), and two equivalent Se(11) atoms. In the fourth Tl site, Tl(4) is bonded in a 2-coordinate geometry to one Se(10) and one Se(8) atom. There are eleven inequivalent Se sites. In the first Se site, Se(11) is bonded in a 5-coordinate geometry to one Nb(1), two equivalent Tl(2), and two equivalent Tl(3) atoms. In the second Se site, Se(1) is bonded in a distorted single-bond geometry to one Nb(1), one Tl(2), and one Se(9) atom. In the third Se site, Se(2) is bonded in a 4-coordinate geometry to one Nb(2), one Tl(1), one Tl(3), and one Se(5) atom. In the fourth Se site, Se(3) is bonded in a 4-coordinate geometry to one Nb(1), one Nb(2), one Tl(3), and one Se(7) atom. In the fifth Se site, Se(4) is bonded in a 3-coordinate geometry to one Nb(2), one Tl(1), and one Se(6) atom. In the sixth Se site, Se(5) is bonded in a 2-coordinate geometry to one Nb(2) and one Se(2) atom. In the seventh Se site, Se(6) is bonded in a 3-coordinate geometry to one Nb(1), one Nb(2), and one Se(4) atom. In the eighth Se site, Se(7) is bonded in a distorted single-bond geometry to one Nb(1), one Tl(2), and one Se(3) atom. In the ninth Se site, Se(8) is bonded in a 4-coordinate geometry to one Nb(2), one Tl(4), and two equivalent Tl(1) atoms. In the tenth Se site, Se(9) is bonded in a distorted single-bond geometry to one Nb(1) and one Se(1) atom. In the eleventh Se site, Se(10) is bonded in a distorted see-saw-like geometry to one Nb(1), one Nb(2), one Tl(3), and one Tl(4) atom.
Nb2Tl4Se11 crystallizes in the triclinic P-1 space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one Se(1), one Se(10), one Se(11), one Se(3), one Se(6), one Se(7), and one Se(9) atom to form distorted face-sharing NbSe7 pentagonal bipyramids. The Nb(1)-Se(1) bond length is 2.60 Å. The Nb(1)-Se(10) bond length is 2.68 Å. The Nb(1)-Se(11) bond length is 2.46 Å. The Nb(1)-Se(3) bond length is 2.68 Å. The Nb(1)-Se(6) bond length is 2.88 Å. The Nb(1)-Se(7) bond length is 2.57 Å. The Nb(1)-Se(9) bond length is 2.60 Å. In the second Nb site, Nb(2) is bonded to one Se(10), one Se(2), one Se(3), one Se(4), one Se(5), one Se(6), and one Se(8) atom to form distorted face-sharing NbSe7 pentagonal bipyramids. The Nb(2)-Se(10) bond length is 2.65 Å. The Nb(2)-Se(2) bond length is 2.63 Å. The Nb(2)-Se(3) bond length is 2.91 Å. The Nb(2)-Se(4) bond length is 2.58 Å. The Nb(2)-Se(5) bond length is 2.59 Å. The Nb(2)-Se(6) bond length is 2.65 Å. The Nb(2)-Se(8) bond length is 2.43 Å. There are four inequivalent Tl sites. In the first Tl site, Tl(1) is bonded in a 4-coordinate geometry to one Se(2), one Se(4), and two equivalent Se(8) atoms. The Tl(1)-Se(2) bond length is 3.18 Å. The Tl(1)-Se(4) bond length is 3.34 Å. There is one shorter (3.22 Å) and one longer (3.29 Å) Tl(1)-Se(8) bond length. In the second Tl site, Tl(2) is bonded in a 4-coordinate geometry to one Se(1), one Se(7), and two equivalent Se(11) atoms. The Tl(2)-Se(1) bond length is 3.29 Å. The Tl(2)-Se(7) bond length is 3.40 Å. There is one shorter (3.06 Å) and one longer (3.14 Å) Tl(2)-Se(11) bond length. In the third Tl site, Tl(3) is bonded in a 5-coordinate geometry to one Se(10), one Se(2), one Se(3), and two equivalent Se(11) atoms. The Tl(3)-Se(10) bond length is 3.11 Å. The Tl(3)-Se(2) bond length is 3.32 Å. The Tl(3)-Se(3) bond length is 3.28 Å. There is one shorter (3.22 Å) and one longer (3.29 Å) Tl(3)-Se(11) bond length. In the fourth Tl site, Tl(4) is bonded in a 2-coordinate geometry to one Se(10) and one Se(8) atom. The Tl(4)-Se(10) bond length is 3.14 Å. The Tl(4)-Se(8) bond length is 3.08 Å. There are eleven inequivalent Se sites. In the first Se site, Se(11) is bonded in a 5-coordinate geometry to one Nb(1), two equivalent Tl(2), and two equivalent Tl(3) atoms. In the second Se site, Se(1) is bonded in a distorted single-bond geometry to one Nb(1), one Tl(2), and one Se(9) atom. The Se(1)-Se(9) bond length is 2.38 Å. In the third Se site, Se(2) is bonded in a 4-coordinate geometry to one Nb(2), one Tl(1), one Tl(3), and one Se(5) atom. The Se(2)-Se(5) bond length is 2.37 Å. In the fourth Se site, Se(3) is bonded in a 4-coordinate geometry to one Nb(1), one Nb(2), one Tl(3), and one Se(7) atom. The Se(3)-Se(7) bond length is 2.37 Å. In the fifth Se site, Se(4) is bonded in a 3-coordinate geometry to one Nb(2), one Tl(1), and one Se(6) atom. The Se(4)-Se(6) bond length is 2.36 Å. In the sixth Se site, Se(5) is bonded in a 2-coordinate geometry to one Nb(2) and one Se(2) atom. In the seventh Se site, Se(6) is bonded in a 3-coordinate geometry to one Nb(1), one Nb(2), and one Se(4) atom. In the eighth Se site, Se(7) is bonded in a distorted single-bond geometry to one Nb(1), one Tl(2), and one Se(3) atom. In the ninth Se site, Se(8) is bonded in a 4-coordinate geometry to one Nb(2), one Tl(4), and two equivalent Tl(1) atoms. In the tenth Se site, Se(9) is bonded in a distorted single-bond geometry to one Nb(1) and one Se(1) atom. In the eleventh Se site, Se(10) is bonded in a distorted see-saw-like geometry to one Nb(1), one Nb(2), one Tl(3), and one Tl(4) atom.