K2CuGa3Se6 crystallizes in the monoclinic C2/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 7-coordinate geometry to one Se(1), one Se(2), one Se(3), one Se(5), one Se(6), and two equivalent Se(4) atoms. In the second K site, K(2) is bonded in a 7-coordinate geometry to one Se(1), one Se(3), one Se(4), one Se(5), one Se(6), and two equivalent Se(2) atoms. Cu(1) is bonded to one Se(1), one Se(3), one Se(5), and one Se(6) atom to form CuSe4 tetrahedra that share corners with two equivalent Ga(1)Se4 tetrahedra, corners with two equivalent Ga(2)Se4 tetrahedra, corners with two equivalent Ga(3)Se4 tetrahedra, and corners with two equivalent Ga(4)Se4 tetrahedra. There are four inequivalent Ga sites. In the first Ga site, Ga(1) is bonded to one Se(2), one Se(4), one Se(5), and one Se(6) atom to form GaSe4 tetrahedra that share  a cornercorner with one Ga(3)Se4 tetrahedra,  a cornercorner with one Ga(4)Se4 tetrahedra, corners with two equivalent Cu(1)Se4 tetrahedra, and corners with two equivalent Ga(2)Se4 tetrahedra. In the second Ga site, Ga(2) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form GaSe4 tetrahedra that share  a cornercorner with one Ga(3)Se4 tetrahedra,  a cornercorner with one Ga(4)Se4 tetrahedra, corners with two equivalent Cu(1)Se4 tetrahedra, and corners with two equivalent Ga(1)Se4 tetrahedra. In the third Ga site, Ga(3) is bonded to two equivalent Se(3) and two equivalent Se(6) atoms to form GaSe4 tetrahedra that share corners with two equivalent Ga(1)Se4 tetrahedra, corners with two equivalent Ga(2)Se4 tetrahedra, and corners with four equivalent Cu(1)Se4 tetrahedra. In the fourth Ga site, Ga(4) is bonded to two equivalent Se(1) and two equivalent Se(5) atoms to form GaSe4 tetrahedra that share corners with two equivalent Ga(1)Se4 tetrahedra, corners with two equivalent Ga(2)Se4 tetrahedra, and corners with four equivalent Cu(1)Se4 tetrahedra. There are six inequivalent Se sites. In the first Se site, Se(6) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Cu(1), one Ga(1), and one Ga(3) atom. In the second Se site, Se(1) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Cu(1), one Ga(2), and one Ga(4) atom. In the third Se site, Se(2) is bonded in a 5-coordinate geometry to one K(1), two equivalent K(2), one Ga(1), and one Ga(2) atom. In the fourth Se site, Se(3) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Cu(1), one Ga(2), and one Ga(3) atom. In the fifth Se site, Se(4) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Ga(1), and one Ga(2) atom. In the sixth Se site, Se(5) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Cu(1), one Ga(1), and one Ga(4) atom.
K2CuGa3Se6 crystallizes in the monoclinic C2/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 7-coordinate geometry to one Se(1), one Se(2), one Se(3), one Se(5), one Se(6), and two equivalent Se(4) atoms. The K(1)-Se(1) bond length is 3.42 Å. The K(1)-Se(2) bond length is 3.38 Å. The K(1)-Se(3) bond length is 3.49 Å. The K(1)-Se(5) bond length is 3.45 Å. The K(1)-Se(6) bond length is 3.49 Å. There is one shorter (3.40 Å) and one longer (3.74 Å) K(1)-Se(4) bond length. In the second K site, K(2) is bonded in a 7-coordinate geometry to one Se(1), one Se(3), one Se(4), one Se(5), one Se(6), and two equivalent Se(2) atoms. The K(2)-Se(1) bond length is 3.50 Å. The K(2)-Se(3) bond length is 3.41 Å. The K(2)-Se(4) bond length is 3.39 Å. The K(2)-Se(5) bond length is 3.49 Å. The K(2)-Se(6) bond length is 3.45 Å. There is one shorter (3.39 Å) and one longer (3.74 Å) K(2)-Se(2) bond length. Cu(1) is bonded to one Se(1), one Se(3), one Se(5), and one Se(6) atom to form CuSe4 tetrahedra that share corners with two equivalent Ga(1)Se4 tetrahedra, corners with two equivalent Ga(2)Se4 tetrahedra, corners with two equivalent Ga(3)Se4 tetrahedra, and corners with two equivalent Ga(4)Se4 tetrahedra. The Cu(1)-Se(1) bond length is 2.44 Å. The Cu(1)-Se(3) bond length is 2.44 Å. The Cu(1)-Se(5) bond length is 2.46 Å. The Cu(1)-Se(6) bond length is 2.46 Å. There are four inequivalent Ga sites. In the first Ga site, Ga(1) is bonded to one Se(2), one Se(4), one Se(5), and one Se(6) atom to form GaSe4 tetrahedra that share  a cornercorner with one Ga(3)Se4 tetrahedra,  a cornercorner with one Ga(4)Se4 tetrahedra, corners with two equivalent Cu(1)Se4 tetrahedra, and corners with two equivalent Ga(2)Se4 tetrahedra. The Ga(1)-Se(2) bond length is 2.47 Å. The Ga(1)-Se(4) bond length is 2.47 Å. The Ga(1)-Se(5) bond length is 2.44 Å. The Ga(1)-Se(6) bond length is 2.44 Å. In the second Ga site, Ga(2) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form GaSe4 tetrahedra that share  a cornercorner with one Ga(3)Se4 tetrahedra,  a cornercorner with one Ga(4)Se4 tetrahedra, corners with two equivalent Cu(1)Se4 tetrahedra, and corners with two equivalent Ga(1)Se4 tetrahedra. The Ga(2)-Se(1) bond length is 2.43 Å. The Ga(2)-Se(2) bond length is 2.47 Å. The Ga(2)-Se(3) bond length is 2.44 Å. The Ga(2)-Se(4) bond length is 2.47 Å. In the third Ga site, Ga(3) is bonded to two equivalent Se(3) and two equivalent Se(6) atoms to form GaSe4 tetrahedra that share corners with two equivalent Ga(1)Se4 tetrahedra, corners with two equivalent Ga(2)Se4 tetrahedra, and corners with four equivalent Cu(1)Se4 tetrahedra. Both Ga(3)-Se(3) bond lengths are 2.44 Å. Both Ga(3)-Se(6) bond lengths are 2.46 Å. In the fourth Ga site, Ga(4) is bonded to two equivalent Se(1) and two equivalent Se(5) atoms to form GaSe4 tetrahedra that share corners with two equivalent Ga(1)Se4 tetrahedra, corners with two equivalent Ga(2)Se4 tetrahedra, and corners with four equivalent Cu(1)Se4 tetrahedra. Both Ga(4)-Se(1) bond lengths are 2.44 Å. Both Ga(4)-Se(5) bond lengths are 2.46 Å. There are six inequivalent Se sites. In the first Se site, Se(6) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Cu(1), one Ga(1), and one Ga(3) atom. In the second Se site, Se(1) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Cu(1), one Ga(2), and one Ga(4) atom. In the third Se site, Se(2) is bonded in a 5-coordinate geometry to one K(1), two equivalent K(2), one Ga(1), and one Ga(2) atom. In the fourth Se site, Se(3) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Cu(1), one Ga(2), and one Ga(3) atom. In the fifth Se site, Se(4) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Ga(1), and one Ga(2) atom. In the sixth Se site, Se(5) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Cu(1), one Ga(1), and one Ga(4) atom.