DOE OSTI2020
U2(AlSn)3 crystallizes in the orthorhombic Pmmm space group. The structure is three-dimensional. U is bonded to six Al and six Sn atoms to form UAl6Sn6 cuboctahedra that share corners with twelve equivalent UAl6Sn6 cuboctahedra, edges with twelve AlU4Al2Sn6 cuboctahedra, edges with twelve SnU4Al4Sn4 cuboctahedra, faces with six equivalent UAl6Sn6 cuboctahedra, faces with six AlU4Al2Sn6 cuboctahedra, and faces with six SnU4Al4Sn4 cuboctahedra. There are two shorter (3.13 Å) and four longer (3.15 Å) U–Al bond lengths. There are a spread of U–Sn bond distances ranging from 3.14–3.18 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded to four equivalent U, two equivalent Al, and six Sn atoms to form distorted AlU4Al2Sn6 cuboctahedra that share corners with twelve equivalent AlU4Al2Sn6 cuboctahedra, edges with four equivalent AlU4Al4Sn4 cuboctahedra, edges with eight equivalent UAl6Sn6 cuboctahedra, edges with twelve SnU4Al4Sn4 cuboctahedra, faces with four equivalent UAl6Sn6 cuboctahedra, faces with six SnU4Al4Sn4 cuboctahedra, and faces with eight AlU4Al2Sn6 cuboctahedra. Both Al–Al bond lengths are 3.07 Å. There are a spread of Al–Sn bond distances ranging from 3.06–3.25 Å. In the second Al site, Al is bonded to four equivalent U, four equivalent Al, and four equivalent Sn atoms to form distorted AlU4Al4Sn4 cuboctahedra that share corners with four equivalent AlU4Al4Sn4 cuboctahedra, corners with eight equivalent SnU4Al4Sn4 cuboctahedra, edges with eight equivalent UAl6Sn6 cuboctahedra, edges with eight equivalent AlU4Al2Sn6 cuboctahedra, edges with eight equivalent SnU4Al4Sn4 cuboctahedra, faces with four equivalent UAl6Sn6 cuboctahedra, faces with six SnU4Al4Sn4 cuboctahedra, and faces with eight AlU4Al2Sn6 cuboctahedra. All Al–Sn bond lengths are 3.15 Å. There are three inequivalent Sn sites. In the first Sn site, Sn is bonded to four equivalent U, four equivalent Al, and four equivalent Sn atoms to form distorted SnU4Al4Sn4 cuboctahedra that share corners with four equivalent SnU4Al4Sn4 cuboctahedra, corners with eight equivalent AlU4Al4Sn4 cuboctahedra, edges with eight equivalent UAl6Sn6 cuboctahedra, edges with eight equivalent AlU4Al2Sn6 cuboctahedra, edges with eight equivalent SnU4Al8 cuboctahedra, faces with four equivalent UAl6Sn6 cuboctahedra, faces with six AlU4Al2Sn6 cuboctahedra, and faces with eight SnU4Al4Sn4 cuboctahedra. All Sn–Sn bond lengths are 3.15 Å. In the second Sn site, Sn is bonded to four equivalent U and eight Al atoms to form SnU4Al8 cuboctahedra that share corners with twelve SnU4Al8 cuboctahedra, edges with eight equivalent UAl6Sn6 cuboctahedra, edges with eight equivalent AlU4Al2Sn6 cuboctahedra, edges with eight equivalent SnU4Al4Sn4 cuboctahedra, faces with four equivalent UAl6Sn6 cuboctahedra, faces with six SnU4Al8 cuboctahedra, and faces with eight AlU4Al2Sn6 cuboctahedra. In the third Sn site, Sn is bonded to four equivalent U, four equivalent Al, and four equivalent Sn atoms to form distorted SnU4Al4Sn4 cuboctahedra that share corners with twelve SnU4Al8 cuboctahedra, edges with eight equivalent UAl6Sn6 cuboctahedra, edges with sixteen AlU4Al2Sn6 cuboctahedra, faces with four equivalent UAl6Sn6 cuboctahedra, faces with four equivalent AlU4Al2Sn6 cuboctahedra, and faces with ten SnU4Al4Sn4 cuboctahedra.