Pr3Al4Si6 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 9-coordinate geometry to three equivalent Si(3) and six equivalent Si(2) atoms. In the second Pr site, Pr(2) is bonded to six equivalent Si(1) atoms to form distorted PrSi6 octahedra that share corners with six equivalent Al(1)Si4 tetrahedra, corners with six equivalent Al(2)Si4 tetrahedra, edges with six equivalent Pr(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(1) and three equivalent Si(3) atoms to form AlSi4 tetrahedra that share corners with three equivalent Pr(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 52°. In the second Al site, Al(2) is bonded to one Si(3) and three equivalent Si(1) atoms to form AlSi4 tetrahedra that share corners with three equivalent Pr(2)Si6 octahedra, corners with six equivalent Al(2)Si4 tetrahedra, edges with three equivalent Pr(2)Si6 octahedra, and edges with three equivalent Al(1)Si4 tetrahedra. The corner-sharing octahedral tilt angles are 23°. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to three equivalent Pr(2), one Al(1), and three equivalent Al(2) atoms to form a mixture of distorted edge and corner-sharing SiPr3Al4 pentagonal bipyramids. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to six equivalent Pr(1) and three equivalent Si(2) atoms. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to three equivalent Pr(1), one Al(2), and three equivalent Al(1) atoms.
Pr3Al4Si6 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 9-coordinate geometry to three equivalent Si(3) and six equivalent Si(2) atoms. All Pr(1)-Si(3) bond lengths are 3.12 Å. There are three shorter (3.12 Å) and three longer (3.20 Å) Pr(1)-Si(2) bond lengths. In the second Pr site, Pr(2) is bonded to six equivalent Si(1) atoms to form distorted PrSi6 octahedra that share corners with six equivalent Al(1)Si4 tetrahedra, corners with six equivalent Al(2)Si4 tetrahedra, edges with six equivalent Pr(2)Si6 octahedra, and edges with six equivalent Al(2)Si4 tetrahedra. All Pr(2)-Si(1) bond lengths are 3.07 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one Si(1) and three equivalent Si(3) atoms to form AlSi4 tetrahedra that share corners with three equivalent Pr(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 52°. The Al(1)-Si(1) bond length is 2.53 Å. All Al(1)-Si(3) bond lengths are 2.50 Å. In the second Al site, Al(2) is bonded to one Si(3) and three equivalent Si(1) atoms to form AlSi4 tetrahedra that share corners with three equivalent Pr(2)Si6 octahedra, corners with six equivalent Al(2)Si4 tetrahedra, edges with three equivalent Pr(2)Si6 octahedra, and edges with three equivalent Al(1)Si4 tetrahedra. The corner-sharing octahedral tilt angles are 23°. The Al(2)-Si(3) bond length is 2.54 Å. All Al(2)-Si(1) bond lengths are 2.50 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to three equivalent Pr(2), one Al(1), and three equivalent Al(2) atoms to form a mixture of distorted edge and corner-sharing SiPr3Al4 pentagonal bipyramids. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to six equivalent Pr(1) and three equivalent Si(2) atoms. All Si(2)-Si(2) bond lengths are 2.42 Å. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to three equivalent Pr(1), one Al(2), and three equivalent Al(1) atoms.