SiB4 crystallizes in the trigonal R-3m space group. There are two inequivalent B sites. In the first B site, B(1) is bonded in a 6-coordinate geometry to two equivalent B(1), three equivalent B(2), one Si(1), and one Si(2) atom. In the second B site, B(2) is bonded in a 6-coordinate geometry to three equivalent B(1) and three equivalent B(2) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 4-coordinate geometry to three equivalent B(1) and one Si(2) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to six equivalent B(1) and two equivalent Si(1) atoms.
SiB4 crystallizes in the trigonal R-3m space group. There are two inequivalent B sites. In the first B site, B(1) is bonded in a 6-coordinate geometry to two equivalent B(1), three equivalent B(2), one Si(1), and one Si(2) atom. Both B(1)-B(1) bond lengths are 1.75 Å. There are two shorter (1.83 Å) and one longer (1.86 Å) B(1)-B(2) bond length. The B(1)-Si(1) bond length is 2.01 Å. The B(1)-Si(2) bond length is 2.63 Å. In the second B site, B(2) is bonded in a 6-coordinate geometry to three equivalent B(1) and three equivalent B(2) atoms. There is one shorter (1.85 Å) and two longer (1.92 Å) B(2)-B(2) bond lengths. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 4-coordinate geometry to three equivalent B(1) and one Si(2) atom. The Si(1)-Si(2) bond length is 2.17 Å. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to six equivalent B(1) and two equivalent Si(1) atoms.