BC5 crystallizes in the trigonal P3m1 space group. B(1) is bonded to one C(1) and three equivalent C(5) atoms to form BC4 tetrahedra that share corners with three equivalent C(2)C4 tetrahedra, corners with three equivalent C(3)C4 tetrahedra, and corners with six equivalent B(1)C4 tetrahedra. There are five inequivalent C sites. In the first C site, C(1) is bonded to one B(1) and three equivalent C(2) atoms to form CBC3 tetrahedra that share corners with three equivalent C(5)B3C tetrahedra, corners with three equivalent C(4)C4 tetrahedra, and corners with six equivalent C(1)BC3 tetrahedra. In the second C site, C(2) is bonded to one C(4) and three equivalent C(1) atoms to form CC4 tetrahedra that share corners with three equivalent B(1)C4 tetrahedra, corners with three equivalent C(3)C4 tetrahedra, and corners with six equivalent C(2)C4 tetrahedra. In the third C site, C(3) is bonded to one C(5) and three equivalent C(4) atoms to form CC4 tetrahedra that share corners with three equivalent B(1)C4 tetrahedra, corners with three equivalent C(2)C4 tetrahedra, and corners with six equivalent C(3)C4 tetrahedra. In the fourth C site, C(4) is bonded to one C(2) and three equivalent C(3) atoms to form CC4 tetrahedra that share corners with three equivalent C(5)B3C tetrahedra, corners with three equivalent C(1)BC3 tetrahedra, and corners with six equivalent C(4)C4 tetrahedra. In the fifth C site, C(5) is bonded to three equivalent B(1) and one C(3) atom to form distorted CB3C tetrahedra that share corners with three equivalent C(1)BC3 tetrahedra, corners with three equivalent C(4)C4 tetrahedra, and corners with six equivalent C(5)B3C tetrahedra.
BC5 crystallizes in the trigonal P3m1 space group. B(1) is bonded to one C(1) and three equivalent C(5) atoms to form BC4 tetrahedra that share corners with three equivalent C(2)C4 tetrahedra, corners with three equivalent C(3)C4 tetrahedra, and corners with six equivalent B(1)C4 tetrahedra. The B(1)-C(1) bond length is 1.61 Å. All B(1)-C(5) bond lengths are 1.63 Å. There are five inequivalent C sites. In the first C site, C(1) is bonded to one B(1) and three equivalent C(2) atoms to form CBC3 tetrahedra that share corners with three equivalent C(5)B3C tetrahedra, corners with three equivalent C(4)C4 tetrahedra, and corners with six equivalent C(1)BC3 tetrahedra. All C(1)-C(2) bond lengths are 1.56 Å. In the second C site, C(2) is bonded to one C(4) and three equivalent C(1) atoms to form CC4 tetrahedra that share corners with three equivalent B(1)C4 tetrahedra, corners with three equivalent C(3)C4 tetrahedra, and corners with six equivalent C(2)C4 tetrahedra. The C(2)-C(4) bond length is 1.55 Å. In the third C site, C(3) is bonded to one C(5) and three equivalent C(4) atoms to form CC4 tetrahedra that share corners with three equivalent B(1)C4 tetrahedra, corners with three equivalent C(2)C4 tetrahedra, and corners with six equivalent C(3)C4 tetrahedra. The C(3)-C(5) bond length is 1.50 Å. All C(3)-C(4) bond lengths are 1.57 Å. In the fourth C site, C(4) is bonded to one C(2) and three equivalent C(3) atoms to form CC4 tetrahedra that share corners with three equivalent C(5)B3C tetrahedra, corners with three equivalent C(1)BC3 tetrahedra, and corners with six equivalent C(4)C4 tetrahedra. In the fifth C site, C(5) is bonded to three equivalent B(1) and one C(3) atom to form distorted CB3C tetrahedra that share corners with three equivalent C(1)BC3 tetrahedra, corners with three equivalent C(4)C4 tetrahedra, and corners with six equivalent C(5)B3C tetrahedra.