EuAu4Al8Si crystallizes in the tetragonal P4mm space group. Eu(1) is bonded in a 16-coordinate geometry to four equivalent Au(4), four equivalent Al(1), four equivalent Al(2), and four equivalent Si(1) atoms. There are four inequivalent Au sites. In the first Au site, Au(1) is bonded in a body-centered cubic geometry to four equivalent Al(3) and four equivalent Al(4) atoms. In the second Au site, Au(2) is bonded in a body-centered cubic geometry to four equivalent Al(1) and four equivalent Al(3) atoms. In the third Au site, Au(3) is bonded in a body-centered cubic geometry to four equivalent Al(2) and four equivalent Al(4) atoms. In the fourth Au site, Au(4) is bonded in a 9-coordinate geometry to four equivalent Eu(1), four equivalent Al(1), and one Si(1) atom. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent Eu(1), two equivalent Au(2), and two equivalent Au(4) atoms to form AlEu2Au4 tetrahedra that share corners with two equivalent Al(1)Eu2Au4 tetrahedra, corners with six equivalent Al(3)Au4 tetrahedra, corners with six equivalent Al(2)Eu2Si2Au2 tetrahedra,  an edgeedge with one Al(3)Au4 tetrahedra,  an edgeedge with one Al(2)Eu2Si2Au2 tetrahedra, edges with two equivalent Al(1)Eu2Au4 tetrahedra, and faces with four equivalent Al(1)Eu2Au4 tetrahedra. In the second Al site, Al(2) is bonded to two equivalent Eu(1), two equivalent Au(3), and two equivalent Si(1) atoms to form distorted AlEu2Si2Au2 tetrahedra that share corners with two equivalent Al(2)Eu2Si2Au2 tetrahedra, corners with six equivalent Al(4)Au4 tetrahedra, corners with six equivalent Al(1)Eu2Au4 tetrahedra,  an edgeedge with one Al(4)Au4 tetrahedra,  an edgeedge with one Al(1)Eu2Au4 tetrahedra, edges with two equivalent Al(2)Eu2Si2Au2 tetrahedra, and faces with four equivalent Al(2)Eu2Si2Au2 tetrahedra. In the third Al site, Al(3) is bonded to two equivalent Au(1) and two equivalent Au(2) atoms to form AlAu4 tetrahedra that share corners with four equivalent Al(3)Au4 tetrahedra, corners with six equivalent Al(4)Au4 tetrahedra, corners with six equivalent Al(1)Eu2Au4 tetrahedra,  an edgeedge with one Al(4)Au4 tetrahedra,  an edgeedge with one Al(1)Eu2Au4 tetrahedra, and edges with four equivalent Al(3)Au4 tetrahedra. In the fourth Al site, Al(4) is bonded to two equivalent Au(1) and two equivalent Au(3) atoms to form AlAu4 tetrahedra that share corners with four equivalent Al(4)Au4 tetrahedra, corners with six equivalent Al(3)Au4 tetrahedra, corners with six equivalent Al(2)Eu2Si2Au2 tetrahedra,  an edgeedge with one Al(3)Au4 tetrahedra,  an edgeedge with one Al(2)Eu2Si2Au2 tetrahedra, and edges with four equivalent Al(4)Au4 tetrahedra. Si(1) is bonded in a 9-coordinate geometry to four equivalent Eu(1), one Au(4), and four equivalent Al(2) atoms.
EuAu4Al8Si crystallizes in the tetragonal P4mm space group. Eu(1) is bonded in a 16-coordinate geometry to four equivalent Au(4), four equivalent Al(1), four equivalent Al(2), and four equivalent Si(1) atoms. All Eu(1)-Au(4) bond lengths are 3.33 Å. All Eu(1)-Al(1) bond lengths are 3.52 Å. All Eu(1)-Al(2) bond lengths are 3.42 Å. All Eu(1)-Si(1) bond lengths are 3.23 Å. There are four inequivalent Au sites. In the first Au site, Au(1) is bonded in a body-centered cubic geometry to four equivalent Al(3) and four equivalent Al(4) atoms. All Au(1)-Al(3) bond lengths are 2.62 Å. All Au(1)-Al(4) bond lengths are 2.62 Å. In the second Au site, Au(2) is bonded in a body-centered cubic geometry to four equivalent Al(1) and four equivalent Al(3) atoms. All Au(2)-Al(1) bond lengths are 2.65 Å. All Au(2)-Al(3) bond lengths are 2.61 Å. In the third Au site, Au(3) is bonded in a body-centered cubic geometry to four equivalent Al(2) and four equivalent Al(4) atoms. All Au(3)-Al(2) bond lengths are 2.59 Å. All Au(3)-Al(4) bond lengths are 2.64 Å. In the fourth Au site, Au(4) is bonded in a 9-coordinate geometry to four equivalent Eu(1), four equivalent Al(1), and one Si(1) atom. All Au(4)-Al(1) bond lengths are 2.58 Å. The Au(4)-Si(1) bond length is 2.47 Å. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent Eu(1), two equivalent Au(2), and two equivalent Au(4) atoms to form AlEu2Au4 tetrahedra that share corners with two equivalent Al(1)Eu2Au4 tetrahedra, corners with six equivalent Al(3)Au4 tetrahedra, corners with six equivalent Al(2)Eu2Si2Au2 tetrahedra,  an edgeedge with one Al(3)Au4 tetrahedra,  an edgeedge with one Al(2)Eu2Si2Au2 tetrahedra, edges with two equivalent Al(1)Eu2Au4 tetrahedra, and faces with four equivalent Al(1)Eu2Au4 tetrahedra. In the second Al site, Al(2) is bonded to two equivalent Eu(1), two equivalent Au(3), and two equivalent Si(1) atoms to form distorted AlEu2Si2Au2 tetrahedra that share corners with two equivalent Al(2)Eu2Si2Au2 tetrahedra, corners with six equivalent Al(4)Au4 tetrahedra, corners with six equivalent Al(1)Eu2Au4 tetrahedra,  an edgeedge with one Al(4)Au4 tetrahedra,  an edgeedge with one Al(1)Eu2Au4 tetrahedra, edges with two equivalent Al(2)Eu2Si2Au2 tetrahedra, and faces with four equivalent Al(2)Eu2Si2Au2 tetrahedra. Both Al(2)-Si(1) bond lengths are 2.65 Å. In the third Al site, Al(3) is bonded to two equivalent Au(1) and two equivalent Au(2) atoms to form AlAu4 tetrahedra that share corners with four equivalent Al(3)Au4 tetrahedra, corners with six equivalent Al(4)Au4 tetrahedra, corners with six equivalent Al(1)Eu2Au4 tetrahedra,  an edgeedge with one Al(4)Au4 tetrahedra,  an edgeedge with one Al(1)Eu2Au4 tetrahedra, and edges with four equivalent Al(3)Au4 tetrahedra. In the fourth Al site, Al(4) is bonded to two equivalent Au(1) and two equivalent Au(3) atoms to form AlAu4 tetrahedra that share corners with four equivalent Al(4)Au4 tetrahedra, corners with six equivalent Al(3)Au4 tetrahedra, corners with six equivalent Al(2)Eu2Si2Au2 tetrahedra,  an edgeedge with one Al(3)Au4 tetrahedra,  an edgeedge with one Al(2)Eu2Si2Au2 tetrahedra, and edges with four equivalent Al(4)Au4 tetrahedra. Si(1) is bonded in a 9-coordinate geometry to four equivalent Eu(1), one Au(4), and four equivalent Al(2) atoms.