Mg25Y4 is alpha-derived structured and crystallizes in the trigonal R3m space group. There are seven inequivalent Mg sites. In the first Mg site, Mg(7) is bonded in a 10-coordinate geometry to three equivalent Mg(2), six equivalent Mg(6), and one Y(1) atom. In the second Mg site, Mg(1) is bonded to one Mg(5), two equivalent Mg(2), four equivalent Mg(3), four equivalent Mg(6), and one Y(2) atom to form a mixture of distorted corner and edge-sharing MgYMg11 cuboctahedra. In the third Mg site, Mg(2) is bonded in a 13-coordinate geometry to one Mg(4), one Mg(7), two equivalent Mg(1), two equivalent Mg(5), two equivalent Mg(6), four equivalent Mg(3), and one Y(2) atom. In the fourth Mg site, Mg(3) is bonded in a 13-coordinate geometry to one Mg(5), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(6), and two equivalent Y(2) atoms. In the fifth Mg site, Mg(4) is bonded in a 12-coordinate geometry to one Mg(2), one Mg(5), two equivalent Mg(6), four equivalent Mg(3), one Y(1), and three equivalent Y(2) atoms. In the sixth Mg site, Mg(5) is bonded in a 11-coordinate geometry to one Mg(1), one Mg(4), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(5), one Y(1), and two equivalent Y(2) atoms. In the seventh Mg site, Mg(6) is bonded in a 12-coordinate geometry to one Mg(2), one Mg(4), one Mg(7), two equivalent Mg(1), two equivalent Mg(3), two equivalent Mg(6), one Y(1), and two equivalent Y(2) atoms. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 16-coordinate geometry to one Mg(7), three equivalent Mg(4), three equivalent Mg(5), six equivalent Mg(6), and three equivalent Y(2) atoms. In the second Y site, Y(2) is bonded in a 16-coordinate geometry to one Mg(1), one Mg(2), two equivalent Mg(5), three equivalent Mg(4), four equivalent Mg(3), four equivalent Mg(6), and one Y(1) atom.
Mg25Y4 is alpha-derived structured and crystallizes in the trigonal R3m space group. There are seven inequivalent Mg sites. In the first Mg site, Mg(7) is bonded in a 10-coordinate geometry to three equivalent Mg(2), six equivalent Mg(6), and one Y(1) atom. All Mg(7)-Mg(2) bond lengths are 3.20 Å. All Mg(7)-Mg(6) bond lengths are 3.43 Å. The Mg(7)-Y(1) bond length is 3.58 Å. In the second Mg site, Mg(1) is bonded to one Mg(5), two equivalent Mg(2), four equivalent Mg(3), four equivalent Mg(6), and one Y(2) atom to form a mixture of distorted corner and edge-sharing MgYMg11 cuboctahedra. The Mg(1)-Mg(5) bond length is 2.97 Å. Both Mg(1)-Mg(2) bond lengths are 3.35 Å. There are two shorter (3.28 Å) and two longer (3.36 Å) Mg(1)-Mg(3) bond lengths. There are two shorter (3.19 Å) and two longer (3.39 Å) Mg(1)-Mg(6) bond lengths. The Mg(1)-Y(2) bond length is 3.20 Å. In the third Mg site, Mg(2) is bonded in a 13-coordinate geometry to one Mg(4), one Mg(7), two equivalent Mg(1), two equivalent Mg(5), two equivalent Mg(6), four equivalent Mg(3), and one Y(2) atom. The Mg(2)-Mg(4) bond length is 3.00 Å. Both Mg(2)-Mg(5) bond lengths are 3.17 Å. Both Mg(2)-Mg(6) bond lengths are 3.39 Å. There are two shorter (3.32 Å) and two longer (3.36 Å) Mg(2)-Mg(3) bond lengths. The Mg(2)-Y(2) bond length is 3.68 Å. In the fourth Mg site, Mg(3) is bonded in a 13-coordinate geometry to one Mg(5), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(6), and two equivalent Y(2) atoms. The Mg(3)-Mg(5) bond length is 3.39 Å. Both Mg(3)-Mg(3) bond lengths are 3.35 Å. There is one shorter (3.19 Å) and one longer (3.39 Å) Mg(3)-Mg(4) bond length. There is one shorter (2.97 Å) and one longer (3.20 Å) Mg(3)-Mg(6) bond length. There is one shorter (3.22 Å) and one longer (3.68 Å) Mg(3)-Y(2) bond length. In the fifth Mg site, Mg(4) is bonded in a 12-coordinate geometry to one Mg(2), one Mg(5), two equivalent Mg(6), four equivalent Mg(3), one Y(1), and three equivalent Y(2) atoms. The Mg(4)-Mg(5) bond length is 2.86 Å. Both Mg(4)-Mg(6) bond lengths are 3.02 Å. The Mg(4)-Y(1) bond length is 3.47 Å. There are two shorter (3.46 Å) and one longer (3.57 Å) Mg(4)-Y(2) bond length. In the sixth Mg site, Mg(5) is bonded in a 11-coordinate geometry to one Mg(1), one Mg(4), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(5), one Y(1), and two equivalent Y(2) atoms. Both Mg(5)-Mg(5) bond lengths are 3.04 Å. The Mg(5)-Y(1) bond length is 3.47 Å. Both Mg(5)-Y(2) bond lengths are 3.46 Å. In the seventh Mg site, Mg(6) is bonded in a 12-coordinate geometry to one Mg(2), one Mg(4), one Mg(7), two equivalent Mg(1), two equivalent Mg(3), two equivalent Mg(6), one Y(1), and two equivalent Y(2) atoms. There is one shorter (2.87 Å) and one longer (3.02 Å) Mg(6)-Mg(6) bond length. The Mg(6)-Y(1) bond length is 3.45 Å. There is one shorter (3.45 Å) and one longer (3.57 Å) Mg(6)-Y(2) bond length. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 16-coordinate geometry to one Mg(7), three equivalent Mg(4), three equivalent Mg(5), six equivalent Mg(6), and three equivalent Y(2) atoms. All Y(1)-Y(2) bond lengths are 3.64 Å. In the second Y site, Y(2) is bonded in a 16-coordinate geometry to one Mg(1), one Mg(2), two equivalent Mg(5), three equivalent Mg(4), four equivalent Mg(3), four equivalent Mg(6), and one Y(1) atom.