U2Al3Si crystallizes in the trigonal R-3m space group. U(1) is bonded in a 16-coordinate geometry to four equivalent U(1), nine equivalent Al(1), and three equivalent Si(1) atoms. Al(1) is bonded to six equivalent U(1), four equivalent Al(1), and two equivalent Si(1) atoms to form AlU6Al4Si2 cuboctahedra that share corners with four equivalent Si(1)U6Al6 cuboctahedra, corners with fourteen equivalent Al(1)U6Al4Si2 cuboctahedra, edges with six equivalent Al(1)U6Al4Si2 cuboctahedra, faces with six equivalent Si(1)U6Al6 cuboctahedra, and faces with twelve equivalent Al(1)U6Al4Si2 cuboctahedra. Si(1) is bonded to six equivalent U(1) and six equivalent Al(1) atoms to form SiU6Al6 cuboctahedra that share corners with six equivalent Si(1)U6Al6 cuboctahedra, corners with twelve equivalent Al(1)U6Al4Si2 cuboctahedra, edges with six equivalent Si(1)U6Al6 cuboctahedra, and faces with eighteen equivalent Al(1)U6Al4Si2 cuboctahedra.
U2Al3Si crystallizes in the trigonal R-3m space group. U(1) is bonded in a 16-coordinate geometry to four equivalent U(1), nine equivalent Al(1), and three equivalent Si(1) atoms. There are three shorter (3.29 Å) and one longer (3.30 Å) U(1)-U(1) bond length. There are six shorter (3.15 Å) and three longer (3.16 Å) U(1)-Al(1) bond lengths. All U(1)-Si(1) bond lengths are 3.14 Å. Al(1) is bonded to six equivalent U(1), four equivalent Al(1), and two equivalent Si(1) atoms to form AlU6Al4Si2 cuboctahedra that share corners with four equivalent Si(1)U6Al6 cuboctahedra, corners with fourteen equivalent Al(1)U6Al4Si2 cuboctahedra, edges with six equivalent Al(1)U6Al4Si2 cuboctahedra, faces with six equivalent Si(1)U6Al6 cuboctahedra, and faces with twelve equivalent Al(1)U6Al4Si2 cuboctahedra. All Al(1)-Al(1) bond lengths are 2.68 Å. Both Al(1)-Si(1) bond lengths are 2.69 Å. Si(1) is bonded to six equivalent U(1) and six equivalent Al(1) atoms to form SiU6Al6 cuboctahedra that share corners with six equivalent Si(1)U6Al6 cuboctahedra, corners with twelve equivalent Al(1)U6Al4Si2 cuboctahedra, edges with six equivalent Si(1)U6Al6 cuboctahedra, and faces with eighteen equivalent Al(1)U6Al4Si2 cuboctahedra.