BaAl2Si2 crystallizes in the orthorhombic Pnma space group. Ba(1) is bonded in a 16-coordinate geometry to four equivalent Al(1), five equivalent Al(2), three equivalent Si(2), and four equivalent Si(1) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to four equivalent Ba(1), one Si(2), and three equivalent Si(1) atoms to form distorted AlBa4Si4 tetrahedra that share corners with six equivalent Al(1)Ba4Si4 tetrahedra, corners with eight equivalent Al(2)Ba5Si4 tetrahedra, edges with two equivalent Al(1)Ba4Si4 tetrahedra, faces with two equivalent Al(1)Ba4Si4 tetrahedra, and faces with six equivalent Al(2)Ba5Si4 tetrahedra. In the second Al site, Al(2) is bonded to five equivalent Ba(1), one Si(1), and three equivalent Si(2) atoms to form distorted AlBa5Si4 tetrahedra that share corners with eight equivalent Al(1)Ba4Si4 tetrahedra, corners with eight equivalent Al(2)Ba5Si4 tetrahedra, edges with two equivalent Al(2)Ba5Si4 tetrahedra, faces with four equivalent Al(2)Ba5Si4 tetrahedra, and faces with six equivalent Al(1)Ba4Si4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to four equivalent Ba(1), one Al(2), and three equivalent Al(1) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to three equivalent Ba(1), one Al(1), and three equivalent Al(2) atoms.
BaAl2Si2 crystallizes in the orthorhombic Pnma space group. Ba(1) is bonded in a 16-coordinate geometry to four equivalent Al(1), five equivalent Al(2), three equivalent Si(2), and four equivalent Si(1) atoms. There are a spread of Ba(1)-Al(1) bond distances ranging from 3.38-3.85 Å. There are a spread of Ba(1)-Al(2) bond distances ranging from 3.67-3.82 Å. There is one shorter (3.28 Å) and two longer (3.34 Å) Ba(1)-Si(2) bond lengths. There are two shorter (3.52 Å) and two longer (3.62 Å) Ba(1)-Si(1) bond lengths. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to four equivalent Ba(1), one Si(2), and three equivalent Si(1) atoms to form distorted AlBa4Si4 tetrahedra that share corners with six equivalent Al(1)Ba4Si4 tetrahedra, corners with eight equivalent Al(2)Ba5Si4 tetrahedra, edges with two equivalent Al(1)Ba4Si4 tetrahedra, faces with two equivalent Al(1)Ba4Si4 tetrahedra, and faces with six equivalent Al(2)Ba5Si4 tetrahedra. The Al(1)-Si(2) bond length is 2.58 Å. There is one shorter (2.54 Å) and two longer (2.55 Å) Al(1)-Si(1) bond lengths. In the second Al site, Al(2) is bonded to five equivalent Ba(1), one Si(1), and three equivalent Si(2) atoms to form distorted AlBa5Si4 tetrahedra that share corners with eight equivalent Al(1)Ba4Si4 tetrahedra, corners with eight equivalent Al(2)Ba5Si4 tetrahedra, edges with two equivalent Al(2)Ba5Si4 tetrahedra, faces with four equivalent Al(2)Ba5Si4 tetrahedra, and faces with six equivalent Al(1)Ba4Si4 tetrahedra. The Al(2)-Si(1) bond length is 2.56 Å. There are two shorter (2.52 Å) and one longer (2.57 Å) Al(2)-Si(2) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to four equivalent Ba(1), one Al(2), and three equivalent Al(1) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to three equivalent Ba(1), one Al(1), and three equivalent Al(2) atoms.