Mg3Mn crystallizes in the orthorhombic Pmm2 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), and four equivalent Mn(1) atoms to form MgMg8Mn4 cuboctahedra that share corners with eight equivalent Mn(1)Mg10Mn2 cuboctahedra, corners with ten equivalent Mg(1)Mg8Mn4 cuboctahedra, edges with two equivalent Mg(1)Mg8Mn4 cuboctahedra, edges with four equivalent Mg(2)Mg8Mn4 cuboctahedra, edges with four equivalent Mn(1)Mg10Mn2 cuboctahedra, edges with eight equivalent Mg(3)Mg10Mn2 cuboctahedra, faces with four equivalent Mg(3)Mg10Mn2 cuboctahedra, faces with four equivalent Mg(1)Mg8Mn4 cuboctahedra, faces with four equivalent Mn(1)Mg10Mn2 cuboctahedra, and faces with eight equivalent Mg(2)Mg8Mn4 cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), and four equivalent Mn(1) atoms to form distorted MgMg8Mn4 cuboctahedra that share corners with eight equivalent Mg(3)Mg10Mn2 cuboctahedra, corners with ten equivalent Mg(2)Mg8Mn4 cuboctahedra, edges with two equivalent Mg(2)Mg8Mn4 cuboctahedra, edges with four equivalent Mg(3)Mg10Mn2 cuboctahedra, edges with four equivalent Mg(1)Mg8Mn4 cuboctahedra, edges with eight equivalent Mn(1)Mg10Mn2 cuboctahedra, faces with four equivalent Mg(3)Mg10Mn2 cuboctahedra, faces with four equivalent Mg(2)Mg8Mn4 cuboctahedra, faces with four equivalent Mn(1)Mg10Mn2 cuboctahedra, and faces with eight equivalent Mg(1)Mg8Mn4 cuboctahedra. In the third Mg site, Mg(3) is bonded to two equivalent Mg(3), four equivalent Mg(1), four equivalent Mg(2), and two equivalent Mn(1) atoms to form distorted MgMg10Mn2 cuboctahedra that share corners with eight equivalent Mg(2)Mg8Mn4 cuboctahedra, corners with ten equivalent Mg(3)Mg10Mn2 cuboctahedra, edges with two equivalent Mg(3)Mg10Mn2 cuboctahedra, edges with four equivalent Mg(2)Mg8Mn4 cuboctahedra, edges with four equivalent Mn(1)Mg10Mn2 cuboctahedra, edges with eight equivalent Mg(1)Mg8Mn4 cuboctahedra, faces with four equivalent Mg(3)Mg10Mn2 cuboctahedra, faces with four equivalent Mg(1)Mg8Mn4 cuboctahedra, faces with four equivalent Mg(2)Mg8Mn4 cuboctahedra, and faces with eight equivalent Mn(1)Mg10Mn2 cuboctahedra. Mn(1) is bonded to two equivalent Mg(3), four equivalent Mg(1), four equivalent Mg(2), and two equivalent Mn(1) atoms to form distorted MnMg10Mn2 cuboctahedra that share corners with eight equivalent Mg(1)Mg8Mn4 cuboctahedra, corners with ten equivalent Mn(1)Mg10Mn2 cuboctahedra, edges with two equivalent Mn(1)Mg10Mn2 cuboctahedra, edges with four equivalent Mg(3)Mg10Mn2 cuboctahedra, edges with four equivalent Mg(1)Mg8Mn4 cuboctahedra, edges with eight equivalent Mg(2)Mg8Mn4 cuboctahedra, faces with four equivalent Mg(1)Mg8Mn4 cuboctahedra, faces with four equivalent Mg(2)Mg8Mn4 cuboctahedra, faces with four equivalent Mn(1)Mg10Mn2 cuboctahedra, and faces with eight equivalent Mg(3)Mg10Mn2 cuboctahedra.
Mg3Mn crystallizes in the orthorhombic Pmm2 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), and four equivalent Mn(1) atoms to form MgMg8Mn4 cuboctahedra that share corners with eight equivalent Mn(1)Mg10Mn2 cuboctahedra, corners with ten equivalent Mg(1)Mg8Mn4 cuboctahedra, edges with two equivalent Mg(1)Mg8Mn4 cuboctahedra, edges with four equivalent Mg(2)Mg8Mn4 cuboctahedra, edges with four equivalent Mn(1)Mg10Mn2 cuboctahedra, edges with eight equivalent Mg(3)Mg10Mn2 cuboctahedra, faces with four equivalent Mg(3)Mg10Mn2 cuboctahedra, faces with four equivalent Mg(1)Mg8Mn4 cuboctahedra, faces with four equivalent Mn(1)Mg10Mn2 cuboctahedra, and faces with eight equivalent Mg(2)Mg8Mn4 cuboctahedra. Both Mg(1)-Mg(1) bond lengths are 3.10 Å. Both Mg(1)-Mg(2) bond lengths are 3.05 Å. All Mg(1)-Mg(3) bond lengths are 3.04 Å. There are two shorter (3.06 Å) and two longer (3.08 Å) Mg(1)-Mn(1) bond lengths. In the second Mg site, Mg(2) is bonded to two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), and four equivalent Mn(1) atoms to form distorted MgMg8Mn4 cuboctahedra that share corners with eight equivalent Mg(3)Mg10Mn2 cuboctahedra, corners with ten equivalent Mg(2)Mg8Mn4 cuboctahedra, edges with two equivalent Mg(2)Mg8Mn4 cuboctahedra, edges with four equivalent Mg(3)Mg10Mn2 cuboctahedra, edges with four equivalent Mg(1)Mg8Mn4 cuboctahedra, edges with eight equivalent Mn(1)Mg10Mn2 cuboctahedra, faces with four equivalent Mg(3)Mg10Mn2 cuboctahedra, faces with four equivalent Mg(2)Mg8Mn4 cuboctahedra, faces with four equivalent Mn(1)Mg10Mn2 cuboctahedra, and faces with eight equivalent Mg(1)Mg8Mn4 cuboctahedra. Both Mg(2)-Mg(2) bond lengths are 3.10 Å. There are two shorter (2.99 Å) and two longer (3.15 Å) Mg(2)-Mg(3) bond lengths. All Mg(2)-Mn(1) bond lengths are 3.01 Å. In the third Mg site, Mg(3) is bonded to two equivalent Mg(3), four equivalent Mg(1), four equivalent Mg(2), and two equivalent Mn(1) atoms to form distorted MgMg10Mn2 cuboctahedra that share corners with eight equivalent Mg(2)Mg8Mn4 cuboctahedra, corners with ten equivalent Mg(3)Mg10Mn2 cuboctahedra, edges with two equivalent Mg(3)Mg10Mn2 cuboctahedra, edges with four equivalent Mg(2)Mg8Mn4 cuboctahedra, edges with four equivalent Mn(1)Mg10Mn2 cuboctahedra, edges with eight equivalent Mg(1)Mg8Mn4 cuboctahedra, faces with four equivalent Mg(3)Mg10Mn2 cuboctahedra, faces with four equivalent Mg(1)Mg8Mn4 cuboctahedra, faces with four equivalent Mg(2)Mg8Mn4 cuboctahedra, and faces with eight equivalent Mn(1)Mg10Mn2 cuboctahedra. Both Mg(3)-Mg(3) bond lengths are 3.10 Å. Both Mg(3)-Mn(1) bond lengths are 3.00 Å. Mn(1) is bonded to two equivalent Mg(3), four equivalent Mg(1), four equivalent Mg(2), and two equivalent Mn(1) atoms to form distorted MnMg10Mn2 cuboctahedra that share corners with eight equivalent Mg(1)Mg8Mn4 cuboctahedra, corners with ten equivalent Mn(1)Mg10Mn2 cuboctahedra, edges with two equivalent Mn(1)Mg10Mn2 cuboctahedra, edges with four equivalent Mg(3)Mg10Mn2 cuboctahedra, edges with four equivalent Mg(1)Mg8Mn4 cuboctahedra, edges with eight equivalent Mg(2)Mg8Mn4 cuboctahedra, faces with four equivalent Mg(1)Mg8Mn4 cuboctahedra, faces with four equivalent Mg(2)Mg8Mn4 cuboctahedra, faces with four equivalent Mn(1)Mg10Mn2 cuboctahedra, and faces with eight equivalent Mg(3)Mg10Mn2 cuboctahedra. Both Mn(1)-Mn(1) bond lengths are 3.10 Å.