Y5Si2B8 crystallizes in the tetragonal P4/mbm space group. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 12-coordinate geometry to two equivalent B(3), three equivalent B(2), four equivalent B(1), and three equivalent Si(1) atoms. In the second Y site, Y(2) is bonded to two equivalent B(3) and four equivalent Si(1) atoms to form corner-sharing YSi4B2 octahedra. The corner-sharing octahedral tilt angles are 57°. There are three inequivalent B sites. In the first B site, B(1) is bonded in a 9-coordinate geometry to four equivalent Y(1), one B(2), two equivalent B(1), and two equivalent B(3) atoms. In the second B site, B(2) is bonded in a 9-coordinate geometry to six equivalent Y(1), one B(2), and two equivalent B(1) atoms. In the third B site, B(3) is bonded in a 9-coordinate geometry to one Y(2), four equivalent Y(1), and four equivalent B(1) atoms. Si(1) is bonded in a 9-coordinate geometry to two equivalent Y(2), six equivalent Y(1), and one Si(1) atom.
Y5Si2B8 crystallizes in the tetragonal P4/mbm space group. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 12-coordinate geometry to two equivalent B(3), three equivalent B(2), four equivalent B(1), and three equivalent Si(1) atoms. Both Y(1)-B(3) bond lengths are 2.70 Å. There are two shorter (2.76 Å) and one longer (2.96 Å) Y(1)-B(2) bond length. There are two shorter (2.64 Å) and two longer (2.72 Å) Y(1)-B(1) bond lengths. There is one shorter (3.07 Å) and two longer (3.14 Å) Y(1)-Si(1) bond lengths. In the second Y site, Y(2) is bonded to two equivalent B(3) and four equivalent Si(1) atoms to form corner-sharing YSi4B2 octahedra. The corner-sharing octahedral tilt angles are 57°. Both Y(2)-B(3) bond lengths are 2.75 Å. All Y(2)-Si(1) bond lengths are 2.91 Å. There are three inequivalent B sites. In the first B site, B(1) is bonded in a 9-coordinate geometry to four equivalent Y(1), one B(2), two equivalent B(1), and two equivalent B(3) atoms. The B(1)-B(2) bond length is 1.76 Å. Both B(1)-B(1) bond lengths are 1.80 Å. Both B(1)-B(3) bond lengths are 1.83 Å. In the second B site, B(2) is bonded in a 9-coordinate geometry to six equivalent Y(1), one B(2), and two equivalent B(1) atoms. The B(2)-B(2) bond length is 1.86 Å. In the third B site, B(3) is bonded in a 9-coordinate geometry to one Y(2), four equivalent Y(1), and four equivalent B(1) atoms. Si(1) is bonded in a 9-coordinate geometry to two equivalent Y(2), six equivalent Y(1), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.35 Å.