K2TaCuSe4 crystallizes in the triclinic P1 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to one Se(4), one Se(5), one Se(7), one Se(8), two equivalent Se(1), and two equivalent Se(6) atoms. In the second K site, K(2) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), one Se(3), one Se(6), two equivalent Se(5), and two equivalent Se(8) atoms. In the third K site, K(3) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), one Se(3), one Se(6), two equivalent Se(4), and two equivalent Se(7) atoms. In the fourth K site, K(4) is bonded in a 8-coordinate geometry to one Se(4), one Se(5), one Se(7), one Se(8), two equivalent Se(2), and two equivalent Se(3) atoms. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one Se(2), one Se(3), one Se(4), and one Se(7) atom to form TaSe4 tetrahedra that share edges with two equivalent Cu(2)Se4 tetrahedra. In the second Ta site, Ta(2) is bonded to one Se(1), one Se(5), one Se(6), and one Se(8) atom to form distorted TaSe4 tetrahedra that share edges with two equivalent Cu(1)Se4 tetrahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Se(1), one Se(5), one Se(6), and one Se(8) atom to form distorted CuSe4 tetrahedra that share edges with two equivalent Ta(2)Se4 tetrahedra. In the second Cu site, Cu(2) is bonded to one Se(2), one Se(3), one Se(4), and one Se(7) atom to form distorted CuSe4 tetrahedra that share edges with two equivalent Ta(1)Se4 tetrahedra. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to one K(2), one K(3), two equivalent K(1), one Ta(2), and one Cu(1) atom. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to one K(2), one K(3), two equivalent K(4), one Ta(1), and one Cu(2) atom. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to one K(2), one K(3), two equivalent K(4), one Ta(1), and one Cu(2) atom. In the fourth Se site, Se(4) is bonded in a 6-coordinate geometry to one K(1), one K(4), two equivalent K(3), one Ta(1), and one Cu(2) atom. In the fifth Se site, Se(5) is bonded in a 6-coordinate geometry to one K(1), one K(4), two equivalent K(2), one Ta(2), and one Cu(1) atom. In the sixth Se site, Se(6) is bonded in a 6-coordinate geometry to one K(2), one K(3), two equivalent K(1), one Ta(2), and one Cu(1) atom. In the seventh Se site, Se(7) is bonded in a 6-coordinate geometry to one K(1), one K(4), two equivalent K(3), one Ta(1), and one Cu(2) atom. In the eighth Se site, Se(8) is bonded in a 6-coordinate geometry to one K(1), one K(4), two equivalent K(2), one Ta(2), and one Cu(1) atom.
K2TaCuSe4 crystallizes in the triclinic P1 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to one Se(4), one Se(5), one Se(7), one Se(8), two equivalent Se(1), and two equivalent Se(6) atoms. The K(1)-Se(4) bond length is 3.63 Å. The K(1)-Se(5) bond length is 3.71 Å. The K(1)-Se(7) bond length is 3.59 Å. The K(1)-Se(8) bond length is 3.73 Å. There is one shorter (3.52 Å) and one longer (3.62 Å) K(1)-Se(1) bond length. There is one shorter (3.52 Å) and one longer (3.56 Å) K(1)-Se(6) bond length. In the second K site, K(2) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), one Se(3), one Se(6), two equivalent Se(5), and two equivalent Se(8) atoms. The K(2)-Se(1) bond length is 3.72 Å. The K(2)-Se(2) bond length is 3.55 Å. The K(2)-Se(3) bond length is 3.64 Å. The K(2)-Se(6) bond length is 3.73 Å. There is one shorter (3.53 Å) and one longer (3.57 Å) K(2)-Se(5) bond length. There is one shorter (3.50 Å) and one longer (3.61 Å) K(2)-Se(8) bond length. In the third K site, K(3) is bonded in a 8-coordinate geometry to one Se(1), one Se(2), one Se(3), one Se(6), two equivalent Se(4), and two equivalent Se(7) atoms. The K(3)-Se(1) bond length is 3.61 Å. The K(3)-Se(2) bond length is 3.78 Å. The K(3)-Se(3) bond length is 3.74 Å. The K(3)-Se(6) bond length is 3.52 Å. There is one shorter (3.54 Å) and one longer (3.55 Å) K(3)-Se(4) bond length. There is one shorter (3.53 Å) and one longer (3.62 Å) K(3)-Se(7) bond length. In the fourth K site, K(4) is bonded in a 8-coordinate geometry to one Se(4), one Se(5), one Se(7), one Se(8), two equivalent Se(2), and two equivalent Se(3) atoms. The K(4)-Se(4) bond length is 3.72 Å. The K(4)-Se(5) bond length is 3.57 Å. The K(4)-Se(7) bond length is 3.75 Å. The K(4)-Se(8) bond length is 3.59 Å. There is one shorter (3.50 Å) and one longer (3.68 Å) K(4)-Se(2) bond length. There is one shorter (3.54 Å) and one longer (3.55 Å) K(4)-Se(3) bond length. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one Se(2), one Se(3), one Se(4), and one Se(7) atom to form TaSe4 tetrahedra that share edges with two equivalent Cu(2)Se4 tetrahedra. The Ta(1)-Se(2) bond length is 2.36 Å. The Ta(1)-Se(3) bond length is 2.44 Å. The Ta(1)-Se(4) bond length is 2.43 Å. The Ta(1)-Se(7) bond length is 2.44 Å. In the second Ta site, Ta(2) is bonded to one Se(1), one Se(5), one Se(6), and one Se(8) atom to form distorted TaSe4 tetrahedra that share edges with two equivalent Cu(1)Se4 tetrahedra. The Ta(2)-Se(1) bond length is 2.41 Å. The Ta(2)-Se(5) bond length is 2.51 Å. The Ta(2)-Se(6) bond length is 2.39 Å. The Ta(2)-Se(8) bond length is 2.39 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Se(1), one Se(5), one Se(6), and one Se(8) atom to form distorted CuSe4 tetrahedra that share edges with two equivalent Ta(2)Se4 tetrahedra. The Cu(1)-Se(1) bond length is 2.47 Å. The Cu(1)-Se(5) bond length is 2.49 Å. The Cu(1)-Se(6) bond length is 2.47 Å. The Cu(1)-Se(8) bond length is 2.48 Å. In the second Cu site, Cu(2) is bonded to one Se(2), one Se(3), one Se(4), and one Se(7) atom to form distorted CuSe4 tetrahedra that share edges with two equivalent Ta(1)Se4 tetrahedra. The Cu(2)-Se(2) bond length is 2.51 Å. The Cu(2)-Se(3) bond length is 2.42 Å. The Cu(2)-Se(4) bond length is 2.41 Å. The Cu(2)-Se(7) bond length is 2.52 Å. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to one K(2), one K(3), two equivalent K(1), one Ta(2), and one Cu(1) atom. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to one K(2), one K(3), two equivalent K(4), one Ta(1), and one Cu(2) atom. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to one K(2), one K(3), two equivalent K(4), one Ta(1), and one Cu(2) atom. In the fourth Se site, Se(4) is bonded in a 6-coordinate geometry to one K(1), one K(4), two equivalent K(3), one Ta(1), and one Cu(2) atom. In the fifth Se site, Se(5) is bonded in a 6-coordinate geometry to one K(1), one K(4), two equivalent K(2), one Ta(2), and one Cu(1) atom. In the sixth Se site, Se(6) is bonded in a 6-coordinate geometry to one K(2), one K(3), two equivalent K(1), one Ta(2), and one Cu(1) atom. In the seventh Se site, Se(7) is bonded in a 6-coordinate geometry to one K(1), one K(4), two equivalent K(3), one Ta(1), and one Cu(2) atom. In the eighth Se site, Se(8) is bonded in a 6-coordinate geometry to one K(1), one K(4), two equivalent K(2), one Ta(2), and one Cu(1) atom.