BSi3 crystallizes in the hexagonal P6_3/mmc space group. B(1) is bonded to twelve equivalent Si(1) atoms to form BSi12 cuboctahedra that share corners with six equivalent B(1)Si12 cuboctahedra, corners with twelve equivalent Si(1)Si8B4 cuboctahedra, edges with eighteen equivalent Si(1)Si8B4 cuboctahedra, faces with eight equivalent B(1)Si12 cuboctahedra, and faces with twelve equivalent Si(1)Si8B4 cuboctahedra. Si(1) is bonded to four equivalent B(1) and eight equivalent Si(1) atoms to form distorted SiSi8B4 cuboctahedra that share corners with four equivalent B(1)Si12 cuboctahedra, corners with fourteen equivalent Si(1)Si8B4 cuboctahedra, edges with six equivalent B(1)Si12 cuboctahedra, edges with twelve equivalent Si(1)Si8B4 cuboctahedra, faces with four equivalent B(1)Si12 cuboctahedra, and faces with sixteen equivalent Si(1)Si8B4 cuboctahedra.
BSi3 crystallizes in the hexagonal P6_3/mmc space group. B(1) is bonded to twelve equivalent Si(1) atoms to form BSi12 cuboctahedra that share corners with six equivalent B(1)Si12 cuboctahedra, corners with twelve equivalent Si(1)Si8B4 cuboctahedra, edges with eighteen equivalent Si(1)Si8B4 cuboctahedra, faces with eight equivalent B(1)Si12 cuboctahedra, and faces with twelve equivalent Si(1)Si8B4 cuboctahedra. There are six shorter (2.51 Å) and six longer (2.64 Å) B(1)-Si(1) bond lengths. Si(1) is bonded to four equivalent B(1) and eight equivalent Si(1) atoms to form distorted SiSi8B4 cuboctahedra that share corners with four equivalent B(1)Si12 cuboctahedra, corners with fourteen equivalent Si(1)Si8B4 cuboctahedra, edges with six equivalent B(1)Si12 cuboctahedra, edges with twelve equivalent Si(1)Si8B4 cuboctahedra, faces with four equivalent B(1)Si12 cuboctahedra, and faces with sixteen equivalent Si(1)Si8B4 cuboctahedra. There are a spread of Si(1)-Si(1) bond distances ranging from 2.47-2.67 Å.