DOE OSTI2020
Mg3(Cu2Al)2 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent Mg sites. In the first Mg site, Mg is bonded in a 12-coordinate geometry to four Mg, eight Cu, and four Al atoms. There are a spread of Mg–Mg bond distances ranging from 3.05–3.13 Å. There are a spread of Mg–Cu bond distances ranging from 2.92–2.99 Å. There are a spread of Mg–Al bond distances ranging from 2.98–3.02 Å. In the second Mg site, Mg is bonded in a 12-coordinate geometry to four Mg, seven Cu, and five Al atoms. The Mg–Mg bond length is 3.17 Å. There are a spread of Mg–Cu bond distances ranging from 2.94–2.99 Å. There are a spread of Mg–Al bond distances ranging from 2.95–3.01 Å. In the third Mg site, Mg is bonded in a 12-coordinate geometry to four Mg, nine Cu, and three equivalent Al atoms. There are one shorter (3.05 Å) and two longer (3.12 Å) Mg–Mg bond lengths. There are a spread of Mg–Cu bond distances ranging from 2.93–2.99 Å. There are one shorter (2.98 Å) and two longer (3.00 Å) Mg–Al bond lengths. There are five inequivalent Cu sites. In the first Cu site, Cu is bonded to six Mg, four Cu, and two equivalent Al atoms to form CuMg6Al2Cu4 cuboctahedra that share corners with five AlMg6Al2Cu4 cuboctahedra, corners with thirteen CuMg6Al2Cu4 cuboctahedra, edges with two equivalent AlMg6Al2Cu4 cuboctahedra, edges with four equivalent CuMg6Al2Cu4 cuboctahedra, faces with six AlMg6Al2Cu4 cuboctahedra, and faces with twelve CuMg6Al3Cu3 cuboctahedra. All Cu–Cu bond lengths are 2.55 Å. Both Cu–Al bond lengths are 2.53 Å. In the second Cu site, Cu is bonded to six Mg, three Cu, and three Al atoms to form distorted CuMg6Al3Cu3 cuboctahedra that share corners with six AlMg6Al2Cu4 cuboctahedra, corners with twelve CuMg6Al2Cu4 cuboctahedra, edges with six equivalent CuMg6Al3Cu3 cuboctahedra, faces with nine CuMg6Al2Cu4 cuboctahedra, and faces with nine AlMg6Al2Cu4 cuboctahedra. There are one shorter (2.56 Å) and one longer (2.57 Å) Cu–Cu bond lengths. There are a spread of Cu–Al bond distances ranging from 2.51–2.55 Å. In the third Cu site, Cu is bonded to six equivalent Mg, four Cu, and two equivalent Al atoms to form distorted CuMg6Al2Cu4 cuboctahedra that share corners with four equivalent AlMg6Cu6 cuboctahedra, corners with fourteen CuMg6Al2Cu4 cuboctahedra, edges with six equivalent CuMg6Al2Cu4 cuboctahedra, faces with six equivalent AlMg6Cu6 cuboctahedra, and faces with twelve CuMg6Al2Cu4 cuboctahedra. Both Cu–Cu bond lengths are 2.57 Å. Both Cu–Al bond lengths are 2.51 Å. In the fourth Cu site, Cu is bonded to six Mg, two equivalent Cu, and four Al atoms to form distorted CuMg6Al4Cu2 cuboctahedra that share corners with four equivalent AlMg6Cu6 cuboctahedra, corners with fourteen CuMg6Al2Cu4 cuboctahedra, edges with six CuMg6Al2Cu4 cuboctahedra, faces with eight CuMg6Al2Cu4 cuboctahedra, and faces with ten AlMg6Al2Cu4 cuboctahedra. There are two shorter (2.51 Å) and two longer (2.55 Å) Cu–Al bond lengths. In the fifth Cu site, Cu is bonded to six Mg, four Cu, and two equivalent Al atoms to form distorted CuMg6Al2Cu4 cuboctahedra that share corners with six AlMg6Al2Cu4 cuboctahedra, corners with twelve CuMg6Al2Cu4 cuboctahedra, edges with six CuMg6Al2Cu4 cuboctahedra, faces with seven AlMg6Al2Cu4 cuboctahedra, and faces with eleven CuMg6Al2Cu4 cuboctahedra. Both Cu–Al bond lengths are 2.51 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded to six Mg, four Cu, and two equivalent Al atoms to form distorted AlMg6Al2Cu4 cuboctahedra that share corners with six AlMg6Al2Cu4 cuboctahedra, corners with twelve CuMg6Al2Cu4 cuboctahedra, edges with six AlMg6Al2Cu4 cuboctahedra, faces with four equivalent AlMg6Al2Cu4 cuboctahedra, and faces with fourteen CuMg6Al2Cu4 cuboctahedra. Both Al–Al bond lengths are 2.53 Å. In the second Al site, Al is bonded to six Mg and six Cu atoms to form distorted AlMg6Cu6 cuboctahedra that share corners with eight AlMg6Al2Cu4 cuboctahedra, corners with ten CuMg6Al2Cu4 cuboctahedra, edges with six AlMg6Al2Cu4 cuboctahedra, a faceface with one AlMg6Al2Cu4 cuboctahedra, and faces with seventeen CuMg6Al2Cu4 cuboctahedra. In the third Al site, Al is bonded to six Mg, four Cu, and two equivalent Al atoms to form AlMg6Al2Cu4 cuboctahedra that share corners with eight AlMg6Cu6 cuboctahedra, corners with ten CuMg6Al2Cu4 cuboctahedra, edges with two equivalent AlMg6Al2Cu4 cuboctahedra, edges with four equivalent CuMg6Al2Cu4 cuboctahedra, faces with six AlMg6Al2Cu4 cuboctahedra, and faces with twelve CuMg6Al3Cu3 cuboctahedra.