K3Ta2AsSe11 crystallizes in the monoclinic Cc space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a 9-coordinate geometry to one Se(10), one Se(11), one Se(2), one Se(3), one Se(8), two equivalent Se(4), and two equivalent Se(6) atoms. In the second K site, K(2) is bonded in a 7-coordinate geometry to one Se(11), one Se(3), one Se(6), one Se(8), one Se(9), and two equivalent Se(1) atoms. In the third K site, K(3) is bonded in a 7-coordinate geometry to one As(1), one Se(2), one Se(6), one Se(7), one Se(9), and two equivalent Se(4) atoms. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one Se(10), one Se(3), one Se(5), one Se(6), one Se(7), one Se(8), and one Se(9) atom to form distorted face-sharing TaSe7 pentagonal bipyramids. In the second Ta site, Ta(2) is bonded to one Se(1), one Se(10), one Se(11), one Se(2), one Se(3), one Se(4), and one Se(7) atom to form distorted face-sharing TaSe7 pentagonal bipyramids. As(1) is bonded in a 4-coordinate geometry to one K(3), one Se(1), one Se(5), and one Se(9) atom. There are eleven inequivalent Se sites. In the first Se site, Se(8) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Ta(1), and one Se(3) atom. In the second Se site, Se(9) is bonded in a distorted L-shaped geometry to one K(2), one K(3), one Ta(1), and one As(1) atom. In the third Se site, Se(10) is bonded in a 4-coordinate geometry to one K(1), one Ta(1), one Ta(2), and one Se(11) atom. In the fourth Se site, Se(11) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Ta(2), and one Se(10) atom. In the fifth Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent K(2), one Ta(2), and one As(1) atom. In the sixth Se site, Se(2) is bonded in a 4-coordinate geometry to one K(1), one K(3), one Ta(2), and one Se(7) atom. In the seventh Se site, Se(3) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Ta(1), one Ta(2), and one Se(8) atom. In the eighth Se site, Se(4) is bonded in a 5-coordinate geometry to two equivalent K(1), two equivalent K(3), and one Ta(2) atom. In the ninth Se site, Se(5) is bonded in an L-shaped geometry to one Ta(1) and one As(1) atom. In the tenth Se site, Se(6) is bonded in a distorted single-bond geometry to one K(2), one K(3), two equivalent K(1), and one Ta(1) atom. In the eleventh Se site, Se(7) is bonded in a 2-coordinate geometry to one K(3), one Ta(1), one Ta(2), and one Se(2) atom.
K3Ta2AsSe11 crystallizes in the monoclinic Cc space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a 9-coordinate geometry to one Se(10), one Se(11), one Se(2), one Se(3), one Se(8), two equivalent Se(4), and two equivalent Se(6) atoms. The K(1)-Se(10) bond length is 3.61 Å. The K(1)-Se(11) bond length is 3.52 Å. The K(1)-Se(2) bond length is 3.53 Å. The K(1)-Se(3) bond length is 3.55 Å. The K(1)-Se(8) bond length is 3.39 Å. There is one shorter (3.44 Å) and one longer (3.56 Å) K(1)-Se(4) bond length. There is one shorter (3.61 Å) and one longer (3.72 Å) K(1)-Se(6) bond length. In the second K site, K(2) is bonded in a 7-coordinate geometry to one Se(11), one Se(3), one Se(6), one Se(8), one Se(9), and two equivalent Se(1) atoms. The K(2)-Se(11) bond length is 3.65 Å. The K(2)-Se(3) bond length is 3.75 Å. The K(2)-Se(6) bond length is 3.56 Å. The K(2)-Se(8) bond length is 3.60 Å. The K(2)-Se(9) bond length is 3.80 Å. There is one shorter (3.45 Å) and one longer (3.56 Å) K(2)-Se(1) bond length. In the third K site, K(3) is bonded in a 7-coordinate geometry to one As(1), one Se(2), one Se(6), one Se(7), one Se(9), and two equivalent Se(4) atoms. The K(3)-As(1) bond length is 3.59 Å. The K(3)-Se(2) bond length is 3.36 Å. The K(3)-Se(6) bond length is 3.43 Å. The K(3)-Se(7) bond length is 3.75 Å. The K(3)-Se(9) bond length is 3.77 Å. There is one shorter (3.32 Å) and one longer (3.54 Å) K(3)-Se(4) bond length. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one Se(10), one Se(3), one Se(5), one Se(6), one Se(7), one Se(8), and one Se(9) atom to form distorted face-sharing TaSe7 pentagonal bipyramids. The Ta(1)-Se(10) bond length is 2.93 Å. The Ta(1)-Se(3) bond length is 2.62 Å. The Ta(1)-Se(5) bond length is 2.64 Å. The Ta(1)-Se(6) bond length is 2.37 Å. The Ta(1)-Se(7) bond length is 2.76 Å. The Ta(1)-Se(8) bond length is 2.60 Å. The Ta(1)-Se(9) bond length is 2.72 Å. In the second Ta site, Ta(2) is bonded to one Se(1), one Se(10), one Se(11), one Se(2), one Se(3), one Se(4), and one Se(7) atom to form distorted face-sharing TaSe7 pentagonal bipyramids. The Ta(2)-Se(1) bond length is 2.66 Å. The Ta(2)-Se(10) bond length is 2.64 Å. The Ta(2)-Se(11) bond length is 2.60 Å. The Ta(2)-Se(2) bond length is 2.65 Å. The Ta(2)-Se(3) bond length is 2.88 Å. The Ta(2)-Se(4) bond length is 2.37 Å. The Ta(2)-Se(7) bond length is 2.69 Å. As(1) is bonded in a 4-coordinate geometry to one K(3), one Se(1), one Se(5), and one Se(9) atom. The As(1)-Se(1) bond length is 2.43 Å. The As(1)-Se(5) bond length is 2.41 Å. The As(1)-Se(9) bond length is 2.48 Å. There are eleven inequivalent Se sites. In the first Se site, Se(8) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Ta(1), and one Se(3) atom. The Se(8)-Se(3) bond length is 2.39 Å. In the second Se site, Se(9) is bonded in a distorted L-shaped geometry to one K(2), one K(3), one Ta(1), and one As(1) atom. In the third Se site, Se(10) is bonded in a 4-coordinate geometry to one K(1), one Ta(1), one Ta(2), and one Se(11) atom. The Se(10)-Se(11) bond length is 2.42 Å. In the fourth Se site, Se(11) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Ta(2), and one Se(10) atom. In the fifth Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent K(2), one Ta(2), and one As(1) atom. In the sixth Se site, Se(2) is bonded in a 4-coordinate geometry to one K(1), one K(3), one Ta(2), and one Se(7) atom. The Se(2)-Se(7) bond length is 2.41 Å. In the seventh Se site, Se(3) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Ta(1), one Ta(2), and one Se(8) atom. In the eighth Se site, Se(4) is bonded in a 5-coordinate geometry to two equivalent K(1), two equivalent K(3), and one Ta(2) atom. In the ninth Se site, Se(5) is bonded in an L-shaped geometry to one Ta(1) and one As(1) atom. In the tenth Se site, Se(6) is bonded in a distorted single-bond geometry to one K(2), one K(3), two equivalent K(1), and one Ta(1) atom. In the eleventh Se site, Se(7) is bonded in a 2-coordinate geometry to one K(3), one Ta(1), one Ta(2), and one Se(2) atom.