K2Ag(AsSe2)3 crystallizes in the monoclinic P2_1/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(2), one Se(3), one Se(6), two equivalent Se(4), and two equivalent Se(5) atoms. In the second K site, K(2) is bonded in a 8-coordinate geometry to one As(1), one Se(2), one Se(3), one Se(4), one Se(5), one Se(6), and two equivalent Se(1) atoms. Ag(1) is bonded to one Se(4), one Se(6), and two equivalent Se(2) atoms to form distorted edge-sharing AgSe4 tetrahedra. There are three inequivalent As sites. In the first As site, As(1) is bonded in a 3-coordinate geometry to one K(2), one Se(1), one Se(2), and one Se(3) atom. In the second As site, As(2) is bonded in a trigonal non-coplanar geometry to one Se(3), one Se(4), and one Se(5) atom. In the third As site, As(3) is bonded in a trigonal non-coplanar geometry to one Se(1), one Se(5), and one Se(6) atom. There are six inequivalent Se sites. In the first Se site, Se(3) is bonded in a distorted rectangular see-saw-like geometry to one K(1), one K(2), one As(1), and one As(2) atom. In the second Se site, Se(4) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Ag(1), and one As(2) atom. In the third Se site, Se(5) is bonded to one K(2), two equivalent K(1), one As(2), and one As(3) atom to form distorted SeK3As2 square pyramids that share corners with two equivalent Se(5)K3As2 square pyramids,  a cornercorner with one Se(1)K2As2 trigonal pyramid, and  an edgeedge with one Se(1)K2As2 trigonal pyramid. In the fourth Se site, Se(6) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Ag(1), and one As(3) atom. In the fifth Se site, Se(1) is bonded to two equivalent K(2), one As(1), and one As(3) atom to form SeK2As2 trigonal pyramids that share  a cornercorner with one Se(5)K3As2 square pyramid, corners with two equivalent Se(1)K2As2 trigonal pyramids, and  an edgeedge with one Se(5)K3As2 square pyramid. In the sixth Se site, Se(2) is bonded in a 5-coordinate geometry to one K(1), one K(2), two equivalent Ag(1), and one As(1) atom.
K2Ag(AsSe2)3 crystallizes in the monoclinic P2_1/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(2), one Se(3), one Se(6), two equivalent Se(4), and two equivalent Se(5) atoms. The K(1)-Se(2) bond length is 3.52 Å. The K(1)-Se(3) bond length is 3.49 Å. The K(1)-Se(6) bond length is 3.50 Å. There is one shorter (3.47 Å) and one longer (3.50 Å) K(1)-Se(4) bond length. There is one shorter (3.44 Å) and one longer (3.60 Å) K(1)-Se(5) bond length. In the second K site, K(2) is bonded in a 8-coordinate geometry to one As(1), one Se(2), one Se(3), one Se(4), one Se(5), one Se(6), and two equivalent Se(1) atoms. The K(2)-As(1) bond length is 3.67 Å. The K(2)-Se(2) bond length is 3.49 Å. The K(2)-Se(3) bond length is 3.71 Å. The K(2)-Se(4) bond length is 3.73 Å. The K(2)-Se(5) bond length is 3.57 Å. The K(2)-Se(6) bond length is 3.45 Å. There is one shorter (3.49 Å) and one longer (3.52 Å) K(2)-Se(1) bond length. Ag(1) is bonded to one Se(4), one Se(6), and two equivalent Se(2) atoms to form distorted edge-sharing AgSe4 tetrahedra. The Ag(1)-Se(4) bond length is 2.71 Å. The Ag(1)-Se(6) bond length is 2.66 Å. There is one shorter (2.74 Å) and one longer (2.84 Å) Ag(1)-Se(2) bond length. There are three inequivalent As sites. In the first As site, As(1) is bonded in a 3-coordinate geometry to one K(2), one Se(1), one Se(2), and one Se(3) atom. The As(1)-Se(1) bond length is 2.46 Å. The As(1)-Se(2) bond length is 2.41 Å. The As(1)-Se(3) bond length is 2.46 Å. In the second As site, As(2) is bonded in a trigonal non-coplanar geometry to one Se(3), one Se(4), and one Se(5) atom. The As(2)-Se(3) bond length is 2.51 Å. The As(2)-Se(4) bond length is 2.38 Å. The As(2)-Se(5) bond length is 2.48 Å. In the third As site, As(3) is bonded in a trigonal non-coplanar geometry to one Se(1), one Se(5), and one Se(6) atom. The As(3)-Se(1) bond length is 2.47 Å. The As(3)-Se(5) bond length is 2.50 Å. The As(3)-Se(6) bond length is 2.36 Å. There are six inequivalent Se sites. In the first Se site, Se(3) is bonded in a distorted rectangular see-saw-like geometry to one K(1), one K(2), one As(1), and one As(2) atom. In the second Se site, Se(4) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Ag(1), and one As(2) atom. In the third Se site, Se(5) is bonded to one K(2), two equivalent K(1), one As(2), and one As(3) atom to form distorted SeK3As2 square pyramids that share corners with two equivalent Se(5)K3As2 square pyramids,  a cornercorner with one Se(1)K2As2 trigonal pyramid, and  an edgeedge with one Se(1)K2As2 trigonal pyramid. In the fourth Se site, Se(6) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Ag(1), and one As(3) atom. In the fifth Se site, Se(1) is bonded to two equivalent K(2), one As(1), and one As(3) atom to form SeK2As2 trigonal pyramids that share  a cornercorner with one Se(5)K3As2 square pyramid, corners with two equivalent Se(1)K2As2 trigonal pyramids, and  an edgeedge with one Se(5)K3As2 square pyramid. In the sixth Se site, Se(2) is bonded in a 5-coordinate geometry to one K(1), one K(2), two equivalent Ag(1), and one As(1) atom.