Ba2SiSe4 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 8-coordinate geometry to one Se(2), three equivalent Se(3), and four equivalent Se(1) atoms. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to one Se(3), four equivalent Se(1), and four equivalent Se(2) atoms. Si(1) is bonded in a tetrahedral geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one Si(1) atom to form a mixture of distorted corner, edge, and face-sharing SeBa4Si square pyramids. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to one Ba(1), four equivalent Ba(2), and one Si(1) atom. In the third Se site, Se(3) is bonded to one Ba(2), three equivalent Ba(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing SeBa4Si trigonal bipyramids.
Ba2SiSe4 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 8-coordinate geometry to one Se(2), three equivalent Se(3), and four equivalent Se(1) atoms. The Ba(1)-Se(2) bond length is 3.59 Å. There is one shorter (3.36 Å) and two longer (3.66 Å) Ba(1)-Se(3) bond lengths. There are two shorter (3.33 Å) and two longer (3.39 Å) Ba(1)-Se(1) bond lengths. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to one Se(3), four equivalent Se(1), and four equivalent Se(2) atoms. The Ba(2)-Se(3) bond length is 3.25 Å. There are two shorter (3.34 Å) and two longer (3.46 Å) Ba(2)-Se(1) bond lengths. There are a spread of Ba(2)-Se(2) bond distances ranging from 3.39-3.74 Å. Si(1) is bonded in a tetrahedral geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. The Si(1)-Se(2) bond length is 2.28 Å. The Si(1)-Se(3) bond length is 2.28 Å. Both Si(1)-Se(1) bond lengths are 2.26 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Ba(1), two equivalent Ba(2), and one Si(1) atom to form a mixture of distorted corner, edge, and face-sharing SeBa4Si square pyramids. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to one Ba(1), four equivalent Ba(2), and one Si(1) atom. In the third Se site, Se(3) is bonded to one Ba(2), three equivalent Ba(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing SeBa4Si trigonal bipyramids.