Al17(BC3)6 crystallizes in the trigonal P321 space group. There are five inequivalent Al sites. In the first Al site, Al(1) is bonded to one C(1), one C(2), one C(5), and one C(6) atom to form AlC4 tetrahedra that share corners with seven equivalent Al(1)C4 tetrahedra,  a cornercorner with one Al(4)C4 trigonal pyramid,  an edgeedge with one Al(5)C5 trigonal bipyramid, and  an edgeedge with one Al(4)C4 trigonal pyramid. In the second Al site, Al(2) is bonded to one C(3), one C(4), one C(7), and one C(8) atom to form a mixture of edge and corner-sharing AlC4 tetrahedra. In the third Al site, Al(3) is bonded to one C(4) and three equivalent C(7) atoms to form a mixture of edge and corner-sharing AlC4 trigonal pyramids. In the fourth Al site, Al(4) is bonded to one C(2) and three equivalent C(1) atoms to form AlC4 trigonal pyramids that share corners with three equivalent Al(1)C4 tetrahedra, corners with three equivalent Al(5)C5 trigonal bipyramids, corners with three equivalent Al(4)C4 trigonal pyramids, and edges with three equivalent Al(1)C4 tetrahedra. In the fifth Al site, Al(5) is bonded to two equivalent C(6) and three equivalent C(1) atoms to form a mixture of edge and corner-sharing AlC5 trigonal bipyramids. There are three inequivalent B sites. In the first B site, B(1) is bonded in a linear geometry to one C(2) and one C(3) atom. In the second B site, B(2) is bonded in a linear geometry to one C(4) and one C(5) atom. In the third B site, B(3) is bonded in a linear geometry to one C(6) and one C(8) atom. There are eight inequivalent C sites. In the first C site, C(7) is bonded in a see-saw-like geometry to two equivalent Al(2) and two equivalent Al(3) atoms. In the second C site, C(8) is bonded to three equivalent Al(2) and one B(3) atom to form CAl3B tetrahedra that share corners with three equivalent C(3)Al3B tetrahedra and corners with three equivalent C(4)Al4B trigonal bipyramids. In the third C site, C(1) is bonded to one Al(5), two equivalent Al(1), and two equivalent Al(4) atoms to form CAl5 trigonal bipyramids that share corners with two equivalent C(5)Al3B tetrahedra, corners with six equivalent C(1)Al5 trigonal bipyramids, and edges with two equivalent C(2)Al4B trigonal bipyramids. In the fourth C site, C(2) is bonded to one Al(4), three equivalent Al(1), and one B(1) atom to form distorted CAl4B trigonal bipyramids that share  a cornercorner with one C(3)Al3B tetrahedra, corners with three equivalent C(5)Al3B tetrahedra, and edges with three equivalent C(1)Al5 trigonal bipyramids. In the fifth C site, C(3) is bonded to three equivalent Al(2) and one B(1) atom to form CAl3B tetrahedra that share corners with three equivalent C(8)Al3B tetrahedra,  a cornercorner with one C(2)Al4B trigonal bipyramid, and corners with three equivalent C(4)Al4B trigonal bipyramids. In the sixth C site, C(4) is bonded to one Al(3), three equivalent Al(2), and one B(2) atom to form distorted corner-sharing CAl4B trigonal bipyramids. In the seventh C site, C(5) is bonded to three equivalent Al(1) and one B(2) atom to form CAl3B tetrahedra that share  a cornercorner with one C(4)Al4B trigonal bipyramid, corners with three equivalent C(2)Al4B trigonal bipyramids, and corners with three equivalent C(1)Al5 trigonal bipyramids. In the eighth C site, C(6) is bonded in a 5-coordinate geometry to one Al(5), three equivalent Al(1), and one B(3) atom.
Al17(BC3)6 crystallizes in the trigonal P321 space group. There are five inequivalent Al sites. In the first Al site, Al(1) is bonded to one C(1), one C(2), one C(5), and one C(6) atom to form AlC4 tetrahedra that share corners with seven equivalent Al(1)C4 tetrahedra,  a cornercorner with one Al(4)C4 trigonal pyramid,  an edgeedge with one Al(5)C5 trigonal bipyramid, and  an edgeedge with one Al(4)C4 trigonal pyramid. The Al(1)-C(1) bond length is 2.05 Å. The Al(1)-C(2) bond length is 2.05 Å. The Al(1)-C(5) bond length is 2.01 Å. The Al(1)-C(6) bond length is 2.00 Å. In the second Al site, Al(2) is bonded to one C(3), one C(4), one C(7), and one C(8) atom to form a mixture of edge and corner-sharing AlC4 tetrahedra. The Al(2)-C(3) bond length is 2.03 Å. The Al(2)-C(4) bond length is 2.11 Å. The Al(2)-C(7) bond length is 2.04 Å. The Al(2)-C(8) bond length is 1.98 Å. In the third Al site, Al(3) is bonded to one C(4) and three equivalent C(7) atoms to form a mixture of edge and corner-sharing AlC4 trigonal pyramids. The Al(3)-C(4) bond length is 2.03 Å. All Al(3)-C(7) bond lengths are 2.03 Å. In the fourth Al site, Al(4) is bonded to one C(2) and three equivalent C(1) atoms to form AlC4 trigonal pyramids that share corners with three equivalent Al(1)C4 tetrahedra, corners with three equivalent Al(5)C5 trigonal bipyramids, corners with three equivalent Al(4)C4 trigonal pyramids, and edges with three equivalent Al(1)C4 tetrahedra. The Al(4)-C(2) bond length is 2.20 Å. All Al(4)-C(1) bond lengths are 1.95 Å. In the fifth Al site, Al(5) is bonded to two equivalent C(6) and three equivalent C(1) atoms to form a mixture of edge and corner-sharing AlC5 trigonal bipyramids. Both Al(5)-C(6) bond lengths are 2.43 Å. All Al(5)-C(1) bond lengths are 1.96 Å. There are three inequivalent B sites. In the first B site, B(1) is bonded in a linear geometry to one C(2) and one C(3) atom. The B(1)-C(2) bond length is 1.45 Å. The B(1)-C(3) bond length is 1.43 Å. In the second B site, B(2) is bonded in a linear geometry to one C(4) and one C(5) atom. The B(2)-C(4) bond length is 1.44 Å. The B(2)-C(5) bond length is 1.44 Å. In the third B site, B(3) is bonded in a linear geometry to one C(6) and one C(8) atom. The B(3)-C(6) bond length is 1.44 Å. The B(3)-C(8) bond length is 1.42 Å. There are eight inequivalent C sites. In the first C site, C(7) is bonded in a see-saw-like geometry to two equivalent Al(2) and two equivalent Al(3) atoms. In the second C site, C(8) is bonded to three equivalent Al(2) and one B(3) atom to form CAl3B tetrahedra that share corners with three equivalent C(3)Al3B tetrahedra and corners with three equivalent C(4)Al4B trigonal bipyramids. In the third C site, C(1) is bonded to one Al(5), two equivalent Al(1), and two equivalent Al(4) atoms to form CAl5 trigonal bipyramids that share corners with two equivalent C(5)Al3B tetrahedra, corners with six equivalent C(1)Al5 trigonal bipyramids, and edges with two equivalent C(2)Al4B trigonal bipyramids. In the fourth C site, C(2) is bonded to one Al(4), three equivalent Al(1), and one B(1) atom to form distorted CAl4B trigonal bipyramids that share  a cornercorner with one C(3)Al3B tetrahedra, corners with three equivalent C(5)Al3B tetrahedra, and edges with three equivalent C(1)Al5 trigonal bipyramids. In the fifth C site, C(3) is bonded to three equivalent Al(2) and one B(1) atom to form CAl3B tetrahedra that share corners with three equivalent C(8)Al3B tetrahedra,  a cornercorner with one C(2)Al4B trigonal bipyramid, and corners with three equivalent C(4)Al4B trigonal bipyramids. In the sixth C site, C(4) is bonded to one Al(3), three equivalent Al(2), and one B(2) atom to form distorted corner-sharing CAl4B trigonal bipyramids. In the seventh C site, C(5) is bonded to three equivalent Al(1) and one B(2) atom to form CAl3B tetrahedra that share  a cornercorner with one C(4)Al4B trigonal bipyramid, corners with three equivalent C(2)Al4B trigonal bipyramids, and corners with three equivalent C(1)Al5 trigonal bipyramids. In the eighth C site, C(6) is bonded in a 5-coordinate geometry to one Al(5), three equivalent Al(1), and one B(3) atom.