K2EuSiSe5 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 3-coordinate geometry to two equivalent Se(1) and four 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(5), two equivalent Se(2), and two equivalent Se(4) atoms. Eu(1) is bonded in a 9-coordinate geometry to one Se(2), two equivalent Se(1), three equivalent Se(3), and three equivalent Se(5) atoms. Si(1) is bonded in a tetrahedral geometry to one Se(1), one Se(2), one Se(3), and one Se(4) atom. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to one K(2), two equivalent K(1), two equivalent Eu(1), and one Si(1) atom. In the second Se site, Se(2) is bonded in a 1-coordinate geometry to two equivalent K(2), one Eu(1), one Si(1), and one Se(5) atom. In the third Se site, Se(3) is bonded in a 1-coordinate geometry to one K(2), three equivalent Eu(1), one Si(1), and one Se(5) atom. In the fourth Se site, Se(4) is bonded in a 7-coordinate geometry to two equivalent K(2), four equivalent K(1), and one Si(1) atom. In the fifth Se site, Se(5) is bonded in a 6-coordinate geometry to one K(2), three equivalent Eu(1), one Se(2), and one Se(3) atom.
K2EuSiSe5 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 3-coordinate geometry to two equivalent Se(1) and four equivalent Se(4) atoms. There is one shorter (3.29 Å) and one longer (3.85 Å) K(1)-Se(1) bond length. There are a spread of K(1)-Se(4) bond distances ranging from 3.40-3.89 Å. In the second K site, K(2) is bonded in a 7-coordinate geometry to one Se(1), one Se(3), one Se(5), two equivalent Se(2), and two equivalent Se(4) atoms. The K(2)-Se(1) bond length is 3.35 Å. The K(2)-Se(3) bond length is 3.37 Å. The K(2)-Se(5) bond length is 3.26 Å. There is one shorter (3.39 Å) and one longer (3.57 Å) K(2)-Se(2) bond length. There is one shorter (3.31 Å) and one longer (3.39 Å) K(2)-Se(4) bond length. Eu(1) is bonded in a 9-coordinate geometry to one Se(2), two equivalent Se(1), three equivalent Se(3), and three equivalent Se(5) atoms. The Eu(1)-Se(2) bond length is 3.53 Å. There is one shorter (3.19 Å) and one longer (3.29 Å) Eu(1)-Se(1) bond length. There are a spread of Eu(1)-Se(3) bond distances ranging from 3.24-3.56 Å. There are a spread of Eu(1)-Se(5) bond distances ranging from 3.08-3.19 Å. Si(1) is bonded in a tetrahedral geometry to one Se(1), one Se(2), one Se(3), and one Se(4) atom. The Si(1)-Se(1) bond length is 2.28 Å. The Si(1)-Se(2) bond length is 2.34 Å. The Si(1)-Se(3) bond length is 2.32 Å. The Si(1)-Se(4) bond length is 2.28 Å. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to one K(2), two equivalent K(1), two equivalent Eu(1), and one Si(1) atom. In the second Se site, Se(2) is bonded in a 1-coordinate geometry to two equivalent K(2), one Eu(1), one Si(1), and one Se(5) atom. The Se(2)-Se(5) bond length is 2.55 Å. In the third Se site, Se(3) is bonded in a 1-coordinate geometry to one K(2), three equivalent Eu(1), one Si(1), and one Se(5) atom. The Se(3)-Se(5) bond length is 2.94 Å. In the fourth Se site, Se(4) is bonded in a 7-coordinate geometry to two equivalent K(2), four equivalent K(1), and one Si(1) atom. In the fifth Se site, Se(5) is bonded in a 6-coordinate geometry to one K(2), three equivalent Eu(1), one Se(2), and one Se(3) atom.