BC7 crystallizes in the orthorhombic Pmm2 space group. B(1) is bonded to two equivalent C(1) and two equivalent C(2) atoms to form BC4 tetrahedra that share corners with two equivalent B(1)C4 tetrahedra, corners with two equivalent C(4)C4 tetrahedra, and corners with eight equivalent C(5)C4 tetrahedra. There are five inequivalent C sites. In the first C site, C(1) is bonded to one B(1), one C(4), and two equivalent C(5) atoms to form distorted CBC3 tetrahedra that share corners with four equivalent C(2)B2C2 tetrahedra, corners with four equivalent C(1)BC3 tetrahedra, and corners with four equivalent C(3)C4 tetrahedra. In the second C site, C(2) is bonded to two equivalent B(1) and two equivalent C(5) atoms to form distorted CB2C2 tetrahedra that share corners with two equivalent C(2)B2C2 tetrahedra, corners with two equivalent C(3)C4 tetrahedra, and corners with eight equivalent C(1)BC3 tetrahedra. In the third C site, C(3) is bonded to two equivalent C(4) and two equivalent C(5) atoms to form CC4 tetrahedra that share corners with two equivalent C(2)B2C2 tetrahedra, corners with two equivalent C(3)C4 tetrahedra, and corners with eight equivalent C(1)BC3 tetrahedra. In the fourth C site, C(4) is bonded to two equivalent C(1) and two equivalent C(3) atoms to form CC4 tetrahedra that share corners with two equivalent B(1)C4 tetrahedra, corners with two equivalent C(4)C4 tetrahedra, and corners with eight equivalent C(5)C4 tetrahedra. In the fifth C site, C(5) is bonded to one C(2), one C(3), and two equivalent C(1) atoms to form CC4 tetrahedra that share corners with four equivalent B(1)C4 tetrahedra, corners with four equivalent C(4)C4 tetrahedra, and corners with four equivalent C(5)C4 tetrahedra.
BC7 crystallizes in the orthorhombic Pmm2 space group. B(1) is bonded to two equivalent C(1) and two equivalent C(2) atoms to form BC4 tetrahedra that share corners with two equivalent B(1)C4 tetrahedra, corners with two equivalent C(4)C4 tetrahedra, and corners with eight equivalent C(5)C4 tetrahedra. Both B(1)-C(1) bond lengths are 1.60 Å. Both B(1)-C(2) bond lengths are 1.67 Å. There are five inequivalent C sites. In the first C site, C(1) is bonded to one B(1), one C(4), and two equivalent C(5) atoms to form distorted CBC3 tetrahedra that share corners with four equivalent C(2)B2C2 tetrahedra, corners with four equivalent C(1)BC3 tetrahedra, and corners with four equivalent C(3)C4 tetrahedra. The C(1)-C(4) bond length is 1.55 Å. Both C(1)-C(5) bond lengths are 1.54 Å. In the second C site, C(2) is bonded to two equivalent B(1) and two equivalent C(5) atoms to form distorted CB2C2 tetrahedra that share corners with two equivalent C(2)B2C2 tetrahedra, corners with two equivalent C(3)C4 tetrahedra, and corners with eight equivalent C(1)BC3 tetrahedra. Both C(2)-C(5) bond lengths are 1.53 Å. In the third C site, C(3) is bonded to two equivalent C(4) and two equivalent C(5) atoms to form CC4 tetrahedra that share corners with two equivalent C(2)B2C2 tetrahedra, corners with two equivalent C(3)C4 tetrahedra, and corners with eight equivalent C(1)BC3 tetrahedra. Both C(3)-C(4) bond lengths are 1.54 Å. Both C(3)-C(5) bond lengths are 1.58 Å. In the fourth C site, C(4) is bonded to two equivalent C(1) and two equivalent C(3) atoms to form CC4 tetrahedra that share corners with two equivalent B(1)C4 tetrahedra, corners with two equivalent C(4)C4 tetrahedra, and corners with eight equivalent C(5)C4 tetrahedra. In the fifth C site, C(5) is bonded to one C(2), one C(3), and two equivalent C(1) atoms to form CC4 tetrahedra that share corners with four equivalent B(1)C4 tetrahedra, corners with four equivalent C(4)C4 tetrahedra, and corners with four equivalent C(5)C4 tetrahedra.