CsAsSe2 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 9-coordinate geometry to one As(2), one Se(4), two equivalent Se(2), two equivalent Se(3), and three equivalent Se(1) atoms. In the second Cs site, Cs(2) is bonded in a 10-coordinate geometry to two equivalent As(1), two equivalent Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. There are two inequivalent As sites. In the first As site, As(1) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Cs(2), one Se(1), one Se(2), and one Se(4) atom. In the second As site, As(2) is bonded in a 3-coordinate geometry to one Cs(1), one Se(2), one Se(3), and one Se(4) atom. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent Cs(2), three equivalent Cs(1), and one As(1) atom. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent Cs(2), one As(1), and one As(2) atom. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to two equivalent Cs(1), two equivalent Cs(2), and one As(2) atom. In the fourth Se site, Se(4) is bonded in a 2-coordinate geometry to one Cs(1), two equivalent Cs(2), one As(1), and one As(2) atom.
CsAsSe2 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 9-coordinate geometry to one As(2), one Se(4), two equivalent Se(2), two equivalent Se(3), and three equivalent Se(1) atoms. The Cs(1)-As(2) bond length is 3.91 Å. The Cs(1)-Se(4) bond length is 4.17 Å. There is one shorter (3.89 Å) and one longer (3.95 Å) Cs(1)-Se(2) bond length. There is one shorter (3.78 Å) and one longer (3.89 Å) Cs(1)-Se(3) bond length. There are a spread of Cs(1)-Se(1) bond distances ranging from 3.69-3.78 Å. In the second Cs site, Cs(2) is bonded in a 10-coordinate geometry to two equivalent As(1), two equivalent Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. There is one shorter (3.90 Å) and one longer (3.91 Å) Cs(2)-As(1) bond length. There is one shorter (3.75 Å) and one longer (3.96 Å) Cs(2)-Se(1) bond length. There is one shorter (3.75 Å) and one longer (3.78 Å) Cs(2)-Se(2) bond length. There is one shorter (3.77 Å) and one longer (3.85 Å) Cs(2)-Se(3) bond length. There is one shorter (3.78 Å) and one longer (3.89 Å) Cs(2)-Se(4) bond length. There are two inequivalent As sites. In the first As site, As(1) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Cs(2), one Se(1), one Se(2), and one Se(4) atom. The As(1)-Se(1) bond length is 2.31 Å. The As(1)-Se(2) bond length is 2.49 Å. The As(1)-Se(4) bond length is 2.44 Å. In the second As site, As(2) is bonded in a 3-coordinate geometry to one Cs(1), one Se(2), one Se(3), and one Se(4) atom. The As(2)-Se(2) bond length is 2.45 Å. The As(2)-Se(3) bond length is 2.32 Å. The As(2)-Se(4) bond length is 2.46 Å. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent Cs(2), three equivalent Cs(1), and one As(1) atom. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent Cs(2), one As(1), and one As(2) atom. In the third Se site, Se(3) is bonded in a 5-coordinate geometry to two equivalent Cs(1), two equivalent Cs(2), and one As(2) atom. In the fourth Se site, Se(4) is bonded in a 2-coordinate geometry to one Cs(1), two equivalent Cs(2), one As(1), and one As(2) atom.