Al4Cu2Mg8Si7 crystallizes in the monoclinic Pm space group. There are eight inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Si(4), one Si(5), and two equivalent Si(2) atoms to form distorted MgSi4 tetrahedra that share  a cornercorner with one Mg(2)Si4 tetrahedra,  a cornercorner with one Al(4)Si4 tetrahedra, and corners with two equivalent Mg(1)Si4 tetrahedra. In the second Mg site, Mg(2) is bonded to one Si(4), one Si(6), and two equivalent Si(3) atoms to form distorted MgSi4 tetrahedra that share  a cornercorner with one Mg(1)Si4 tetrahedra,  a cornercorner with one Al(4)Si4 tetrahedra, and corners with two equivalent Mg(2)Si4 tetrahedra. In the third Mg site, Mg(3) is bonded in a 7-coordinate geometry to two equivalent Cu(2), one Si(1), two equivalent Si(5), and two equivalent Si(7) atoms. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to two equivalent Cu(2), one Si(2), two equivalent Si(5), and two equivalent Si(6) atoms. In the fifth Mg site, Mg(5) is bonded in a 7-coordinate geometry to two equivalent Cu(2), one Si(3), two equivalent Si(6), and two equivalent Si(7) atoms. In the sixth Mg site, Mg(6) is bonded in a 5-coordinate geometry to one Si(3), two equivalent Si(4), and two equivalent Si(5) atoms. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(1), two equivalent Si(4), and two equivalent Si(6) atoms. In the eighth Mg site, Mg(8) is bonded in a 5-coordinate geometry to one Si(2), two equivalent Si(4), and two equivalent Si(7) atoms. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 9-coordinate geometry to two equivalent Al(1), two equivalent Al(2), two equivalent Al(3), one Si(1), one Si(2), and one Si(3) atom. In the second Cu site, Cu(2) is bonded in a 9-coordinate geometry to two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(5), one Si(5), one Si(6), and one Si(7) atom. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded in a 5-coordinate geometry to two equivalent Cu(1), one Si(5), and two equivalent Si(3) atoms. In the second Al site, Al(2) is bonded in a 7-coordinate geometry to two equivalent Cu(1), one Si(6), two equivalent Si(1), and two equivalent Si(2) atoms. In the third Al site, Al(3) is bonded in a 7-coordinate geometry to two equivalent Cu(1), one Si(7), two equivalent Si(2), and two equivalent Si(3) atoms. In the fourth Al site, Al(4) is bonded to one Si(4), one Si(7), and two equivalent Si(1) atoms to form distorted AlSi4 tetrahedra that share  a cornercorner with one Mg(1)Si4 tetrahedra,  a cornercorner with one Mg(2)Si4 tetrahedra, and corners with two equivalent Al(4)Si4 tetrahedra. There are seven inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to one Mg(3), one Mg(7), one Cu(1), two equivalent Al(2), and two equivalent Al(4) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(4), one Mg(8), two equivalent Mg(1), one Cu(1), two equivalent Al(2), and two equivalent Al(3) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(5), one Mg(6), two equivalent Mg(2), one Cu(1), two equivalent Al(1), and two equivalent Al(3) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(2), two equivalent Mg(6), two equivalent Mg(7), two equivalent Mg(8), and one Al(4) atom. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(6), one Cu(2), and one Al(1) atom. In the sixth Si site, Si(6) is bonded in a 9-coordinate geometry to one Mg(2), two equivalent Mg(4), two equivalent Mg(5), two equivalent Mg(7), one Cu(2), and one Al(2) atom. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to two equivalent Mg(3), two equivalent Mg(5), two equivalent Mg(8), one Cu(2), one Al(3), and one Al(4) atom.
Al4Cu2Mg8Si7 crystallizes in the monoclinic Pm space group. There are eight inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Si(4), one Si(5), and two equivalent Si(2) atoms to form distorted MgSi4 tetrahedra that share  a cornercorner with one Mg(2)Si4 tetrahedra,  a cornercorner with one Al(4)Si4 tetrahedra, and corners with two equivalent Mg(1)Si4 tetrahedra. The Mg(1)-Si(4) bond length is 2.65 Å. The Mg(1)-Si(5) bond length is 2.71 Å. Both Mg(1)-Si(2) bond lengths are 2.65 Å. In the second Mg site, Mg(2) is bonded to one Si(4), one Si(6), and two equivalent Si(3) atoms to form distorted MgSi4 tetrahedra that share  a cornercorner with one Mg(1)Si4 tetrahedra,  a cornercorner with one Al(4)Si4 tetrahedra, and corners with two equivalent Mg(2)Si4 tetrahedra. The Mg(2)-Si(4) bond length is 2.67 Å. The Mg(2)-Si(6) bond length is 2.71 Å. Both Mg(2)-Si(3) bond lengths are 2.65 Å. In the third Mg site, Mg(3) is bonded in a 7-coordinate geometry to two equivalent Cu(2), one Si(1), two equivalent Si(5), and two equivalent Si(7) atoms. Both Mg(3)-Cu(2) bond lengths are 2.69 Å. The Mg(3)-Si(1) bond length is 2.64 Å. Both Mg(3)-Si(5) bond lengths are 2.84 Å. Both Mg(3)-Si(7) bond lengths are 2.97 Å. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to two equivalent Cu(2), one Si(2), two equivalent Si(5), and two equivalent Si(6) atoms. Both Mg(4)-Cu(2) bond lengths are 2.70 Å. The Mg(4)-Si(2) bond length is 2.75 Å. Both Mg(4)-Si(5) bond lengths are 3.07 Å. Both Mg(4)-Si(6) bond lengths are 2.83 Å. In the fifth Mg site, Mg(5) is bonded in a 7-coordinate geometry to two equivalent Cu(2), one Si(3), two equivalent Si(6), and two equivalent Si(7) atoms. Both Mg(5)-Cu(2) bond lengths are 2.71 Å. The Mg(5)-Si(3) bond length is 2.73 Å. Both Mg(5)-Si(6) bond lengths are 3.05 Å. Both Mg(5)-Si(7) bond lengths are 2.84 Å. In the sixth Mg site, Mg(6) is bonded in a 5-coordinate geometry to one Si(3), two equivalent Si(4), and two equivalent Si(5) atoms. The Mg(6)-Si(3) bond length is 2.83 Å. Both Mg(6)-Si(4) bond lengths are 2.95 Å. Both Mg(6)-Si(5) bond lengths are 2.82 Å. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(1), two equivalent Si(4), and two equivalent Si(6) atoms. The Mg(7)-Si(1) bond length is 2.66 Å. Both Mg(7)-Si(4) bond lengths are 2.92 Å. Both Mg(7)-Si(6) bond lengths are 2.81 Å. In the eighth Mg site, Mg(8) is bonded in a 5-coordinate geometry to one Si(2), two equivalent Si(4), and two equivalent Si(7) atoms. The Mg(8)-Si(2) bond length is 2.83 Å. Both Mg(8)-Si(4) bond lengths are 2.87 Å. Both Mg(8)-Si(7) bond lengths are 2.79 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 9-coordinate geometry to two equivalent Al(1), two equivalent Al(2), two equivalent Al(3), one Si(1), one Si(2), and one Si(3) atom. Both Cu(1)-Al(1) bond lengths are 2.66 Å. Both Cu(1)-Al(2) bond lengths are 2.66 Å. Both Cu(1)-Al(3) bond lengths are 2.94 Å. The Cu(1)-Si(1) bond length is 2.30 Å. The Cu(1)-Si(2) bond length is 2.33 Å. The Cu(1)-Si(3) bond length is 2.33 Å. In the second Cu site, Cu(2) is bonded in a 9-coordinate geometry to two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(5), one Si(5), one Si(6), and one Si(7) atom. The Cu(2)-Si(5) bond length is 2.39 Å. The Cu(2)-Si(6) bond length is 2.37 Å. The Cu(2)-Si(7) bond length is 2.37 Å. There are four inequivalent Al sites. In the first Al site, Al(1) is bonded in a 5-coordinate geometry to two equivalent Cu(1), one Si(5), and two equivalent Si(3) atoms. The Al(1)-Si(5) bond length is 2.57 Å. Both Al(1)-Si(3) bond lengths are 2.75 Å. In the second Al site, Al(2) is bonded in a 7-coordinate geometry to two equivalent Cu(1), one Si(6), two equivalent Si(1), and two equivalent Si(2) atoms. The Al(2)-Si(6) bond length is 2.59 Å. Both Al(2)-Si(1) bond lengths are 2.98 Å. Both Al(2)-Si(2) bond lengths are 2.87 Å. In the third Al site, Al(3) is bonded in a 7-coordinate geometry to two equivalent Cu(1), one Si(7), two equivalent Si(2), and two equivalent Si(3) atoms. The Al(3)-Si(7) bond length is 2.62 Å. Both Al(3)-Si(2) bond lengths are 2.80 Å. Both Al(3)-Si(3) bond lengths are 2.93 Å. In the fourth Al site, Al(4) is bonded to one Si(4), one Si(7), and two equivalent Si(1) atoms to form distorted AlSi4 tetrahedra that share  a cornercorner with one Mg(1)Si4 tetrahedra,  a cornercorner with one Mg(2)Si4 tetrahedra, and corners with two equivalent Al(4)Si4 tetrahedra. The Al(4)-Si(4) bond length is 2.53 Å. The Al(4)-Si(7) bond length is 2.57 Å. Both Al(4)-Si(1) bond lengths are 2.52 Å. There are seven inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to one Mg(3), one Mg(7), one Cu(1), two equivalent Al(2), and two equivalent Al(4) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(4), one Mg(8), two equivalent Mg(1), one Cu(1), two equivalent Al(2), and two equivalent Al(3) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(5), one Mg(6), two equivalent Mg(2), one Cu(1), two equivalent Al(1), and two equivalent Al(3) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(2), two equivalent Mg(6), two equivalent Mg(7), two equivalent Mg(8), and one Al(4) atom. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(6), one Cu(2), and one Al(1) atom. In the sixth Si site, Si(6) is bonded in a 9-coordinate geometry to one Mg(2), two equivalent Mg(4), two equivalent Mg(5), two equivalent Mg(7), one Cu(2), and one Al(2) atom. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to two equivalent Mg(3), two equivalent Mg(5), two equivalent Mg(8), one Cu(2), one Al(3), and one Al(4) atom.