Ca3Cu2Al7 crystallizes in the trigonal R-3m space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 18-coordinate geometry to six equivalent Cu(1) and twelve equivalent Al(2) atoms. In the second Ca site, Ca(2) is bonded in a 12-coordinate geometry to three equivalent Al(1) and nine equivalent Al(2) atoms. Cu(1) is bonded in a 9-coordinate geometry to three equivalent Ca(1) and six equivalent Al(2) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to six equivalent Ca(2) and six equivalent Al(2) atoms to form AlCa6Al6 cuboctahedra that share corners with twelve equivalent Al(2)Ca5Al5Cu2 cuboctahedra, edges with six equivalent Al(1)Ca6Al6 cuboctahedra, and faces with eighteen equivalent Al(2)Ca5Al5Cu2 cuboctahedra. In the second Al site, Al(2) is bonded to two equivalent Ca(1), three equivalent Ca(2), two equivalent Cu(1), one Al(1), and four equivalent Al(2) atoms to form distorted AlCa5Al5Cu2 cuboctahedra that share corners with two equivalent Al(1)Ca6Al6 cuboctahedra, corners with fifteen equivalent Al(2)Ca5Al5Cu2 cuboctahedra, edges with eight equivalent Al(2)Ca5Al5Cu2 cuboctahedra, faces with three equivalent Al(1)Ca6Al6 cuboctahedra, and faces with eleven equivalent Al(2)Ca5Al5Cu2 cuboctahedra.
Ca3Cu2Al7 crystallizes in the trigonal R-3m space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 18-coordinate geometry to six equivalent Cu(1) and twelve equivalent Al(2) atoms. All Ca(1)-Cu(1) bond lengths are 3.21 Å. All Ca(1)-Al(2) bond lengths are 3.40 Å. In the second Ca site, Ca(2) is bonded in a 12-coordinate geometry to three equivalent Al(1) and nine equivalent Al(2) atoms. All Ca(2)-Al(1) bond lengths are 3.26 Å. There are six shorter (3.26 Å) and three longer (3.32 Å) Ca(2)-Al(2) bond lengths. Cu(1) is bonded in a 9-coordinate geometry to three equivalent Ca(1) and six equivalent Al(2) atoms. There are three shorter (2.52 Å) and three longer (2.56 Å) Cu(1)-Al(2) bond lengths. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to six equivalent Ca(2) and six equivalent Al(2) atoms to form AlCa6Al6 cuboctahedra that share corners with twelve equivalent Al(2)Ca5Al5Cu2 cuboctahedra, edges with six equivalent Al(1)Ca6Al6 cuboctahedra, and faces with eighteen equivalent Al(2)Ca5Al5Cu2 cuboctahedra. All Al(1)-Al(2) bond lengths are 2.82 Å. In the second Al site, Al(2) is bonded to two equivalent Ca(1), three equivalent Ca(2), two equivalent Cu(1), one Al(1), and four equivalent Al(2) atoms to form distorted AlCa5Al5Cu2 cuboctahedra that share corners with two equivalent Al(1)Ca6Al6 cuboctahedra, corners with fifteen equivalent Al(2)Ca5Al5Cu2 cuboctahedra, edges with eight equivalent Al(2)Ca5Al5Cu2 cuboctahedra, faces with three equivalent Al(1)Ca6Al6 cuboctahedra, and faces with eleven equivalent Al(2)Ca5Al5Cu2 cuboctahedra. There are two shorter (2.75 Å) and two longer (2.81 Å) Al(2)-Al(2) bond lengths.