Cr20Al3Si9 crystallizes in the orthorhombic C222 space group. There are five inequivalent Cr sites. In the first Cr site, Cr(1) is bonded in a 7-coordinate geometry to one Cr(2), one Al(2), one Si(1), one Si(3), and three equivalent Si(4) atoms. In the second Cr site, Cr(2) is bonded in a 7-coordinate geometry to one Cr(1), one Al(1), one Al(3), one Si(2), and three equivalent Si(4) atoms. In the third Cr site, Cr(3) is bonded in a 7-coordinate geometry to one Cr(3), one Al(1), one Al(3), one Si(4), and three equivalent Si(2) atoms. In the fourth Cr site, Cr(4) is bonded in a 7-coordinate geometry to one Cr(4), one Al(2), one Si(1), one Si(4), and three equivalent Si(3) atoms. In the fifth Cr site, Cr(5) is bonded in a 6-coordinate geometry to two equivalent Cr(5), one Si(2), one Si(3), and two equivalent Si(4) atoms. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded in a distorted q6 geometry to four equivalent Cr(2), four equivalent Cr(3), and two equivalent Al(3) atoms. In the second Al site, Al(2) is bonded in a 10-coordinate geometry to four equivalent Cr(1), four equivalent Cr(4), and two equivalent Si(1) atoms. In the third Al site, Al(3) is bonded in a distorted q6 geometry to four equivalent Cr(2), four equivalent Cr(3), and two equivalent Al(1) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted q6 geometry to four equivalent Cr(1), four equivalent Cr(4), and two equivalent Al(2) atoms. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to two equivalent Cr(2), two equivalent Cr(5), and six equivalent Cr(3) atoms. In the third Si site, Si(3) is bonded in a 10-coordinate geometry to two equivalent Cr(1), two equivalent Cr(5), and six equivalent Cr(4) atoms. In the fourth Si site, Si(4) is bonded in a 10-coordinate geometry to one Cr(3), one Cr(4), two equivalent Cr(5), three equivalent Cr(1), and three equivalent Cr(2) atoms.
Cr20Al3Si9 crystallizes in the orthorhombic C222 space group. There are five inequivalent Cr sites. In the first Cr site, Cr(1) is bonded in a 7-coordinate geometry to one Cr(2), one Al(2), one Si(1), one Si(3), and three equivalent Si(4) atoms. The Cr(1)-Cr(2) bond length is 2.44 Å. The Cr(1)-Al(2) bond length is 2.53 Å. The Cr(1)-Si(1) bond length is 2.50 Å. The Cr(1)-Si(3) bond length is 2.41 Å. There are a spread of Cr(1)-Si(4) bond distances ranging from 2.41-2.64 Å. In the second Cr site, Cr(2) is bonded in a 7-coordinate geometry to one Cr(1), one Al(1), one Al(3), one Si(2), and three equivalent Si(4) atoms. The Cr(2)-Al(1) bond length is 2.56 Å. The Cr(2)-Al(3) bond length is 2.56 Å. The Cr(2)-Si(2) bond length is 2.40 Å. There are a spread of Cr(2)-Si(4) bond distances ranging from 2.41-2.61 Å. In the third Cr site, Cr(3) is bonded in a 7-coordinate geometry to one Cr(3), one Al(1), one Al(3), one Si(4), and three equivalent Si(2) atoms. The Cr(3)-Cr(3) bond length is 2.35 Å. The Cr(3)-Al(1) bond length is 2.57 Å. The Cr(3)-Al(3) bond length is 2.57 Å. The Cr(3)-Si(4) bond length is 2.43 Å. There is one shorter (2.42 Å) and two longer (2.60 Å) Cr(3)-Si(2) bond lengths. In the fourth Cr site, Cr(4) is bonded in a 7-coordinate geometry to one Cr(4), one Al(2), one Si(1), one Si(4), and three equivalent Si(3) atoms. The Cr(4)-Cr(4) bond length is 2.44 Å. The Cr(4)-Al(2) bond length is 2.54 Å. The Cr(4)-Si(1) bond length is 2.52 Å. The Cr(4)-Si(4) bond length is 2.43 Å. There are a spread of Cr(4)-Si(3) bond distances ranging from 2.41-2.64 Å. In the fifth Cr site, Cr(5) is bonded in a 6-coordinate geometry to two equivalent Cr(5), one Si(2), one Si(3), and two equivalent Si(4) atoms. There is one shorter (2.29 Å) and one longer (2.34 Å) Cr(5)-Cr(5) bond length. The Cr(5)-Si(2) bond length is 2.46 Å. The Cr(5)-Si(3) bond length is 2.44 Å. There is one shorter (2.44 Å) and one longer (2.45 Å) Cr(5)-Si(4) bond length. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded in a distorted q6 geometry to four equivalent Cr(2), four equivalent Cr(3), and two equivalent Al(3) atoms. Both Al(1)-Al(3) bond lengths are 2.31 Å. In the second Al site, Al(2) is bonded in a 10-coordinate geometry to four equivalent Cr(1), four equivalent Cr(4), and two equivalent Si(1) atoms. Both Al(2)-Si(1) bond lengths are 2.31 Å. In the third Al site, Al(3) is bonded in a distorted q6 geometry to four equivalent Cr(2), four equivalent Cr(3), and two equivalent Al(1) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted q6 geometry to four equivalent Cr(1), four equivalent Cr(4), and two equivalent Al(2) atoms. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to two equivalent Cr(2), two equivalent Cr(5), and six equivalent Cr(3) atoms. In the third Si site, Si(3) is bonded in a 10-coordinate geometry to two equivalent Cr(1), two equivalent Cr(5), and six equivalent Cr(4) atoms. In the fourth Si site, Si(4) is bonded in a 10-coordinate geometry to one Cr(3), one Cr(4), two equivalent Cr(5), three equivalent Cr(1), and three equivalent Cr(2) atoms.