Ce3Al4Si6 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded in a 9-coordinate geometry to three equivalent Si(2) and six equivalent Si(1) atoms. In the second Ce site, Ce(2) is bonded to six equivalent Si(3) atoms to form CeSi6 octahedra that share corners with six equivalent Al(1)Si4 tetrahedra, corners with six equivalent Al(2)Si4 tetrahedra, edges with six equivalent Ce(2)Si6 octahedra, and edges with six equivalent Al(2)Si4 tetrahedra. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one Si(3) and three equivalent Si(2) atoms to form distorted AlSi4 tetrahedra that share corners with three equivalent Ce(2)Si6 octahedra, corners with six equivalent Al(1)Si4 tetrahedra, and edges with three equivalent Al(2)Si4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. In the second Al site, Al(2) is bonded to one Si(2) and three equivalent Si(3) atoms to form AlSi4 tetrahedra that share corners with three equivalent Ce(2)Si6 octahedra, corners with six equivalent Al(2)Si4 tetrahedra, edges with three equivalent Ce(2)Si6 octahedra, and edges with three equivalent Al(1)Si4 tetrahedra. The corner-sharing octahedral tilt angles are 21°. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to six equivalent Ce(1) and three equivalent Si(1) atoms. In the second Si site, Si(2) is bonded to three equivalent Ce(1), one Al(2), and three equivalent Al(1) atoms to form distorted edge-sharing SiCe3Al4 pentagonal bipyramids. In the third Si site, Si(3) is bonded to three equivalent Ce(2), one Al(1), and three equivalent Al(2) atoms to form a mixture of distorted corner and edge-sharing SiCe3Al4 pentagonal bipyramids.
Ce3Al4Si6 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded in a 9-coordinate geometry to three equivalent Si(2) and six equivalent Si(1) atoms. All Ce(1)-Si(2) bond lengths are 3.05 Å. There are three shorter (3.06 Å) and three longer (3.11 Å) Ce(1)-Si(1) bond lengths. In the second Ce site, Ce(2) is bonded to six equivalent Si(3) atoms to form CeSi6 octahedra that share corners with six equivalent Al(1)Si4 tetrahedra, corners with six equivalent Al(2)Si4 tetrahedra, edges with six equivalent Ce(2)Si6 octahedra, and edges with six equivalent Al(2)Si4 tetrahedra. All Ce(2)-Si(3) bond lengths are 3.01 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one Si(3) and three equivalent Si(2) atoms to form distorted AlSi4 tetrahedra that share corners with three equivalent Ce(2)Si6 octahedra, corners with six equivalent Al(1)Si4 tetrahedra, and edges with three equivalent Al(2)Si4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. The Al(1)-Si(3) bond length is 2.56 Å. All Al(1)-Si(2) bond lengths are 2.49 Å. In the second Al site, Al(2) is bonded to one Si(2) and three equivalent Si(3) atoms to form AlSi4 tetrahedra that share corners with three equivalent Ce(2)Si6 octahedra, corners with six equivalent Al(2)Si4 tetrahedra, edges with three equivalent Ce(2)Si6 octahedra, and edges with three equivalent Al(1)Si4 tetrahedra. The corner-sharing octahedral tilt angles are 21°. The Al(2)-Si(2) bond length is 2.55 Å. All Al(2)-Si(3) bond lengths are 2.49 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to six equivalent Ce(1) and three equivalent Si(1) atoms. All Si(1)-Si(1) bond lengths are 2.40 Å. In the second Si site, Si(2) is bonded to three equivalent Ce(1), one Al(2), and three equivalent Al(1) atoms to form distorted edge-sharing SiCe3Al4 pentagonal bipyramids. In the third Si site, Si(3) is bonded to three equivalent Ce(2), one Al(1), and three equivalent Al(2) atoms to form a mixture of distorted corner and edge-sharing SiCe3Al4 pentagonal bipyramids.