Mg6Cu16Si7 crystallizes in the cubic Fm-3m space group. Mg(1) is bonded in a 12-coordinate geometry to four equivalent Cu(1), four equivalent Cu(2), and four equivalent Si(2) atoms. There are two inequivalent Cu sites. In the first Cu site, Cu(2) is bonded in a 12-coordinate geometry to three equivalent Mg(1), three equivalent Cu(1), three equivalent Cu(2), and three equivalent Si(2) atoms. In the second Cu site, Cu(1) is bonded in a 13-coordinate geometry to three equivalent Mg(1), three equivalent Cu(1), three equivalent Cu(2), one Si(1), and three equivalent Si(2) atoms. There are two inequivalent Si sites. In the first Si site, Si(2) is bonded to four equivalent Mg(1), four equivalent Cu(1), and four equivalent Cu(2) atoms to form a mixture of corner and face-sharing SiMg4Cu8 cuboctahedra. In the second Si site, Si(1) is bonded in a body-centered cubic geometry to eight equivalent Cu(1) atoms.
Mg6Cu16Si7 crystallizes in the cubic Fm-3m space group. Mg(1) is bonded in a 12-coordinate geometry to four equivalent Cu(1), four equivalent Cu(2), and four equivalent Si(2) atoms. All Mg(1)-Cu(1) bond lengths are 2.84 Å. All Mg(1)-Cu(2) bond lengths are 2.78 Å. All Mg(1)-Si(2) bond lengths are 2.94 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(2) is bonded in a 12-coordinate geometry to three equivalent Mg(1), three equivalent Cu(1), three equivalent Cu(2), and three equivalent Si(2) atoms. All Cu(2)-Cu(1) bond lengths are 2.58 Å. All Cu(2)-Cu(2) bond lengths are 2.69 Å. All Cu(2)-Si(2) bond lengths are 2.36 Å. In the second Cu site, Cu(1) is bonded in a 13-coordinate geometry to three equivalent Mg(1), three equivalent Cu(1), three equivalent Cu(2), one Si(1), and three equivalent Si(2) atoms. All Cu(1)-Cu(1) bond lengths are 2.78 Å. The Cu(1)-Si(1) bond length is 2.41 Å. All Cu(1)-Si(2) bond lengths are 2.54 Å. There are two inequivalent Si sites. In the first Si site, Si(2) is bonded to four equivalent Mg(1), four equivalent Cu(1), and four equivalent Cu(2) atoms to form a mixture of corner and face-sharing SiMg4Cu8 cuboctahedra. In the second Si site, Si(1) is bonded in a body-centered cubic geometry to eight equivalent Cu(1) atoms.