K4As2Se5 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent K sites. In the first K site, K(1) is bonded to one Se(1), one Se(4), two equivalent Se(3), and two equivalent Se(5) atoms to form KSe6 octahedra that share corners with two equivalent K(2)Se6 octahedra, corners with two equivalent K(3)Se6 octahedra,  a cornercorner with one As(1)AsSe3 tetrahedra,  an edgeedge with one K(2)Se6 octahedra, edges with two equivalent K(1)Se6 octahedra, edges with four equivalent K(3)Se6 octahedra, and  an edgeedge with one As(1)AsSe3 tetrahedra. The corner-sharing octahedral tilt angles range from 12-15°. In the second K site, K(2) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(4) atoms to form distorted KSe6 octahedra that share corners with two equivalent K(1)Se6 octahedra, corners with two equivalent K(2)Se6 octahedra, corners with two equivalent K(3)Se6 octahedra, corners with two equivalent As(1)AsSe3 tetrahedra,  an edgeedge with one K(1)Se6 octahedra,  an edgeedge with one K(3)Se6 octahedra, edges with two equivalent K(2)Se6 octahedra, and  an edgeedge with one As(1)AsSe3 tetrahedra. The corner-sharing octahedral tilt angles range from 12-19°. In the third K site, K(3) is bonded to one Se(1), one Se(4), two equivalent Se(3), and two equivalent Se(5) atoms to form KSe6 octahedra that share corners with two equivalent K(1)Se6 octahedra, corners with two equivalent K(2)Se6 octahedra, corners with three equivalent As(1)AsSe3 tetrahedra,  an edgeedge with one K(2)Se6 octahedra, edges with two equivalent K(3)Se6 octahedra, and edges with four equivalent K(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 14-15°. In the fourth K site, K(4) is bonded in a 7-coordinate geometry to one As(2), one Se(1), one Se(3), one Se(4), one Se(5), and two equivalent Se(2) atoms. There are two inequivalent As sites. In the first As site, As(1) is bonded to one As(2), one Se(1), one Se(2), and one Se(3) atom to form distorted AsAsSe3 tetrahedra that share  a cornercorner with one K(1)Se6 octahedra,  a cornercorner with one Se(4)K5As octahedra,  a cornercorner with one Se(5)K5As octahedra, corners with two equivalent K(2)Se6 octahedra, corners with three equivalent K(3)Se6 octahedra,  an edgeedge with one K(1)Se6 octahedra, and  an edgeedge with one K(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 18-78°. In the second As site, As(2) is bonded in a distorted water-like geometry to one K(4), one As(1), one Se(4), and one Se(5) atom. There are five inequivalent Se sites. In the first Se site, Se(3) is bonded to one K(4), two equivalent K(1), two equivalent K(3), and one As(1) atom to form SeK5As octahedra that share  a cornercorner with one Se(4)K5As octahedra, corners with two equivalent Se(1)K5As octahedra, corners with three equivalent Se(5)K5As octahedra,  a cornercorner with one Se(2)K4As trigonal bipyramid, edges with two equivalent Se(1)K5As octahedra, edges with two equivalent Se(3)K5As octahedra, edges with two equivalent Se(4)K5As octahedra, edges with three equivalent Se(5)K5As octahedra, and  an edgeedge with one Se(2)K4As trigonal bipyramid. The corner-sharing octahedral tilt angles range from 8-97°. In the second Se site, Se(4) is bonded to one K(1), one K(3), one K(4), two equivalent K(2), and one As(2) atom to form distorted SeK5As octahedra that share  a cornercorner with one Se(1)K5As octahedra,  a cornercorner with one Se(3)K5As octahedra, corners with two equivalent Se(4)K5As octahedra, corners with two equivalent Se(5)K5As octahedra,  a cornercorner with one As(1)AsSe3 tetrahedra, corners with two equivalent Se(2)K4As trigonal bipyramids, edges with two equivalent Se(3)K5As octahedra, edges with two equivalent Se(5)K5As octahedra, edges with three equivalent Se(1)K5As octahedra, and edges with two equivalent Se(2)K4As trigonal bipyramids. The corner-sharing octahedral tilt angles range from 8-97°. In the third Se site, Se(5) is bonded to one K(4), two equivalent K(1), two equivalent K(3), and one As(2) atom to form distorted SeK5As octahedra that share  a cornercorner with one Se(1)K5As octahedra, corners with two equivalent Se(4)K5As octahedra, corners with three equivalent Se(3)K5As octahedra,  a cornercorner with one As(1)AsSe3 tetrahedra, corners with two equivalent Se(2)K4As trigonal bipyramids, edges with two equivalent Se(1)K5As octahedra, edges with two equivalent Se(4)K5As octahedra, edges with two equivalent Se(5)K5As octahedra, and edges with three equivalent Se(3)K5As octahedra. The corner-sharing octahedral tilt angles range from 8-97°. In the fourth Se site, Se(1) is bonded to one K(1), one K(3), one K(4), two equivalent K(2), and one As(1) atom to form distorted SeK5As octahedra that share  a cornercorner with one Se(4)K5As octahedra,  a cornercorner with one Se(5)K5As octahedra, corners with two equivalent Se(1)K5As octahedra, corners with two equivalent Se(3)K5As octahedra,  a cornercorner with one Se(2)K4As trigonal bipyramid, edges with two equivalent Se(3)K5As octahedra, edges with two equivalent Se(5)K5As octahedra, edges with three equivalent Se(4)K5As octahedra, and edges with three equivalent Se(2)K4As trigonal bipyramids. The corner-sharing octahedral tilt angles range from 8-97°. In the fifth Se site, Se(2) is bonded to two equivalent K(2), two equivalent K(4), and one As(1) atom to form distorted SeK4As trigonal bipyramids that share  a cornercorner with one Se(1)K5As octahedra,  a cornercorner with one Se(3)K5As octahedra, corners with two equivalent Se(4)K5As octahedra, corners with two equivalent Se(5)K5As octahedra, corners with four equivalent Se(2)K4As trigonal bipyramids,  an edgeedge with one Se(3)K5As octahedra, edges with two equivalent Se(4)K5As octahedra, and edges with three equivalent Se(1)K5As octahedra. The corner-sharing octahedral tilt angles range from 10-99°.
K4As2Se5 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent K sites. In the first K site, K(1) is bonded to one Se(1), one Se(4), two equivalent Se(3), and two equivalent Se(5) atoms to form KSe6 octahedra that share corners with two equivalent K(2)Se6 octahedra, corners with two equivalent K(3)Se6 octahedra,  a cornercorner with one As(1)AsSe3 tetrahedra,  an edgeedge with one K(2)Se6 octahedra, edges with two equivalent K(1)Se6 octahedra, edges with four equivalent K(3)Se6 octahedra, and  an edgeedge with one As(1)AsSe3 tetrahedra. The corner-sharing octahedral tilt angles range from 12-15°. The K(1)-Se(1) bond length is 3.33 Å. The K(1)-Se(4) bond length is 3.32 Å. There is one shorter (3.27 Å) and one longer (3.52 Å) K(1)-Se(3) bond length. There is one shorter (3.25 Å) and one longer (3.44 Å) K(1)-Se(5) bond length. In the second K site, K(2) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(4) atoms to form distorted KSe6 octahedra that share corners with two equivalent K(1)Se6 octahedra, corners with two equivalent K(2)Se6 octahedra, corners with two equivalent K(3)Se6 octahedra, corners with two equivalent As(1)AsSe3 tetrahedra,  an edgeedge with one K(1)Se6 octahedra,  an edgeedge with one K(3)Se6 octahedra, edges with two equivalent K(2)Se6 octahedra, and  an edgeedge with one As(1)AsSe3 tetrahedra. The corner-sharing octahedral tilt angles range from 12-19°. There is one shorter (3.45 Å) and one longer (3.48 Å) K(2)-Se(1) bond length. There is one shorter (3.32 Å) and one longer (3.33 Å) K(2)-Se(2) bond length. There is one shorter (3.45 Å) and one longer (3.52 Å) K(2)-Se(4) bond length. In the third K site, K(3) is bonded to one Se(1), one Se(4), two equivalent Se(3), and two equivalent Se(5) atoms to form KSe6 octahedra that share corners with two equivalent K(1)Se6 octahedra, corners with two equivalent K(2)Se6 octahedra, corners with three equivalent As(1)AsSe3 tetrahedra,  an edgeedge with one K(2)Se6 octahedra, edges with two equivalent K(3)Se6 octahedra, and edges with four equivalent K(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 14-15°. The K(3)-Se(1) bond length is 3.35 Å. The K(3)-Se(4) bond length is 3.35 Å. There is one shorter (3.34 Å) and one longer (3.39 Å) K(3)-Se(3) bond length. There is one shorter (3.35 Å) and one longer (3.36 Å) K(3)-Se(5) bond length. In the fourth K site, K(4) is bonded in a 7-coordinate geometry to one As(2), one Se(1), one Se(3), one Se(4), one Se(5), and two equivalent Se(2) atoms. The K(4)-As(2) bond length is 3.69 Å. The K(4)-Se(1) bond length is 3.77 Å. The K(4)-Se(3) bond length is 3.35 Å. The K(4)-Se(4) bond length is 3.53 Å. The K(4)-Se(5) bond length is 3.39 Å. There is one shorter (3.26 Å) and one longer (3.35 Å) K(4)-Se(2) bond length. There are two inequivalent As sites. In the first As site, As(1) is bonded to one As(2), one Se(1), one Se(2), and one Se(3) atom to form distorted AsAsSe3 tetrahedra that share  a cornercorner with one K(1)Se6 octahedra,  a cornercorner with one Se(4)K5As octahedra,  a cornercorner with one Se(5)K5As octahedra, corners with two equivalent K(2)Se6 octahedra, corners with three equivalent K(3)Se6 octahedra,  an edgeedge with one K(1)Se6 octahedra, and  an edgeedge with one K(2)Se6 octahedra. The corner-sharing octahedral tilt angles range from 18-78°. The As(1)-As(2) bond length is 2.55 Å. The As(1)-Se(1) bond length is 2.33 Å. The As(1)-Se(2) bond length is 2.35 Å. The As(1)-Se(3) bond length is 2.35 Å. In the second As site, As(2) is bonded in a distorted water-like geometry to one K(4), one As(1), one Se(4), and one Se(5) atom. The As(2)-Se(4) bond length is 2.34 Å. The As(2)-Se(5) bond length is 2.36 Å. There are five inequivalent Se sites. In the first Se site, Se(3) is bonded to one K(4), two equivalent K(1), two equivalent K(3), and one As(1) atom to form SeK5As octahedra that share  a cornercorner with one Se(4)K5As octahedra, corners with two equivalent Se(1)K5As octahedra, corners with three equivalent Se(5)K5As octahedra,  a cornercorner with one Se(2)K4As trigonal bipyramid, edges with two equivalent Se(1)K5As octahedra, edges with two equivalent Se(3)K5As octahedra, edges with two equivalent Se(4)K5As octahedra, edges with three equivalent Se(5)K5As octahedra, and  an edgeedge with one Se(2)K4As trigonal bipyramid. The corner-sharing octahedral tilt angles range from 8-97°. In the second Se site, Se(4) is bonded to one K(1), one K(3), one K(4), two equivalent K(2), and one As(2) atom to form distorted SeK5As octahedra that share  a cornercorner with one Se(1)K5As octahedra,  a cornercorner with one Se(3)K5As octahedra, corners with two equivalent Se(4)K5As octahedra, corners with two equivalent Se(5)K5As octahedra,  a cornercorner with one As(1)AsSe3 tetrahedra, corners with two equivalent Se(2)K4As trigonal bipyramids, edges with two equivalent Se(3)K5As octahedra, edges with two equivalent Se(5)K5As octahedra, edges with three equivalent Se(1)K5As octahedra, and edges with two equivalent Se(2)K4As trigonal bipyramids. The corner-sharing octahedral tilt angles range from 8-97°. In the third Se site, Se(5) is bonded to one K(4), two equivalent K(1), two equivalent K(3), and one As(2) atom to form distorted SeK5As octahedra that share  a cornercorner with one Se(1)K5As octahedra, corners with two equivalent Se(4)K5As octahedra, corners with three equivalent Se(3)K5As octahedra,  a cornercorner with one As(1)AsSe3 tetrahedra, corners with two equivalent Se(2)K4As trigonal bipyramids, edges with two equivalent Se(1)K5As octahedra, edges with two equivalent Se(4)K5As octahedra, edges with two equivalent Se(5)K5As octahedra, and edges with three equivalent Se(3)K5As octahedra. The corner-sharing octahedral tilt angles range from 8-97°. In the fourth Se site, Se(1) is bonded to one K(1), one K(3), one K(4), two equivalent K(2), and one As(1) atom to form distorted SeK5As octahedra that share  a cornercorner with one Se(4)K5As octahedra,  a cornercorner with one Se(5)K5As octahedra, corners with two equivalent Se(1)K5As octahedra, corners with two equivalent Se(3)K5As octahedra,  a cornercorner with one Se(2)K4As trigonal bipyramid, edges with two equivalent Se(3)K5As octahedra, edges with two equivalent Se(5)K5As octahedra, edges with three equivalent Se(4)K5As octahedra, and edges with three equivalent Se(2)K4As trigonal bipyramids. The corner-sharing octahedral tilt angles range from 8-97°. In the fifth Se site, Se(2) is bonded to two equivalent K(2), two equivalent K(4), and one As(1) atom to form distorted SeK4As trigonal bipyramids that share  a cornercorner with one Se(1)K5As octahedra,  a cornercorner with one Se(3)K5As octahedra, corners with two equivalent Se(4)K5As octahedra, corners with two equivalent Se(5)K5As octahedra, corners with four equivalent Se(2)K4As trigonal bipyramids,  an edgeedge with one Se(3)K5As octahedra, edges with two equivalent Se(4)K5As octahedra, and edges with three equivalent Se(1)K5As octahedra. The corner-sharing octahedral tilt angles range from 10-99°.