Mg2Ga crystallizes in the monoclinic Cm space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(2), two equivalent Mg(3), three equivalent Mg(4), one Ga(2), and two equivalent Ga(1) atoms to form distorted MgMg7Ga3 cuboctahedra that share corners with two equivalent Mg(4)Mg8Ga4 cuboctahedra, corners with four equivalent Mg(1)Mg7Ga3 cuboctahedra, corners with eight equivalent Mg(2)Mg7Ga5 cuboctahedra,  an edgeedge with one Mg(2)Mg7Ga5 cuboctahedra, faces with two equivalent Mg(1)Mg7Ga3 cuboctahedra, faces with three equivalent Mg(2)Mg7Ga5 cuboctahedra, and faces with five equivalent Mg(4)Mg8Ga4 cuboctahedra. In the second Mg site, Mg(2) is bonded to one Mg(4), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Ga(2), and three equivalent Ga(1) atoms to form distorted MgMg7Ga5 cuboctahedra that share corners with six equivalent Mg(2)Mg7Ga5 cuboctahedra, corners with eight equivalent Mg(1)Mg7Ga3 cuboctahedra,  an edgeedge with one Mg(1)Mg7Ga3 cuboctahedra, edges with four equivalent Mg(4)Mg8Ga4 cuboctahedra, faces with two equivalent Mg(2)Mg7Ga5 cuboctahedra, faces with three equivalent Mg(1)Mg7Ga3 cuboctahedra, and faces with four equivalent Mg(4)Mg8Ga4 cuboctahedra. In the third Mg site, Mg(3) is bonded in a 12-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), one Ga(1), and three equivalent Ga(2) atoms. In the fourth Mg site, Mg(4) is bonded to one Mg(2), two equivalent Mg(3), two equivalent Mg(4), three equivalent Mg(1), two equivalent Ga(1), and two equivalent Ga(2) atoms to form distorted MgMg8Ga4 cuboctahedra that share corners with two equivalent Mg(1)Mg7Ga3 cuboctahedra, corners with six equivalent Mg(4)Mg8Ga4 cuboctahedra, edges with four equivalent Mg(2)Mg7Ga5 cuboctahedra, faces with two equivalent Mg(4)Mg8Ga4 cuboctahedra, faces with four equivalent Mg(2)Mg7Ga5 cuboctahedra, and faces with five equivalent Mg(1)Mg7Ga3 cuboctahedra. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded in a 8-coordinate geometry to one Mg(3), two equivalent Mg(1), two equivalent Mg(4), and three equivalent Mg(2) atoms. In the second Ga site, Ga(2) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Mg(2), two equivalent Mg(4), and three equivalent Mg(3) atoms.
Mg2Ga crystallizes in the monoclinic Cm space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(2), two equivalent Mg(3), three equivalent Mg(4), one Ga(2), and two equivalent Ga(1) atoms to form distorted MgMg7Ga3 cuboctahedra that share corners with two equivalent Mg(4)Mg8Ga4 cuboctahedra, corners with four equivalent Mg(1)Mg7Ga3 cuboctahedra, corners with eight equivalent Mg(2)Mg7Ga5 cuboctahedra,  an edgeedge with one Mg(2)Mg7Ga5 cuboctahedra, faces with two equivalent Mg(1)Mg7Ga3 cuboctahedra, faces with three equivalent Mg(2)Mg7Ga5 cuboctahedra, and faces with five equivalent Mg(4)Mg8Ga4 cuboctahedra. Both Mg(1)-Mg(2) bond lengths are 3.17 Å. Both Mg(1)-Mg(3) bond lengths are 3.16 Å. There is one shorter (3.07 Å) and two longer (3.12 Å) Mg(1)-Mg(4) bond lengths. The Mg(1)-Ga(2) bond length is 3.03 Å. Both Mg(1)-Ga(1) bond lengths are 2.98 Å. In the second Mg site, Mg(2) is bonded to one Mg(4), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Ga(2), and three equivalent Ga(1) atoms to form distorted MgMg7Ga5 cuboctahedra that share corners with six equivalent Mg(2)Mg7Ga5 cuboctahedra, corners with eight equivalent Mg(1)Mg7Ga3 cuboctahedra,  an edgeedge with one Mg(1)Mg7Ga3 cuboctahedra, edges with four equivalent Mg(4)Mg8Ga4 cuboctahedra, faces with two equivalent Mg(2)Mg7Ga5 cuboctahedra, faces with three equivalent Mg(1)Mg7Ga3 cuboctahedra, and faces with four equivalent Mg(4)Mg8Ga4 cuboctahedra. The Mg(2)-Mg(4) bond length is 3.07 Å. Both Mg(2)-Mg(2) bond lengths are 3.10 Å. Both Mg(2)-Mg(3) bond lengths are 3.13 Å. Both Mg(2)-Ga(2) bond lengths are 2.95 Å. There are two shorter (3.07 Å) and one longer (3.13 Å) Mg(2)-Ga(1) bond length. In the third Mg site, Mg(3) is bonded in a 12-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), one Ga(1), and three equivalent Ga(2) atoms. Both Mg(3)-Mg(3) bond lengths are 3.10 Å. Both Mg(3)-Mg(4) bond lengths are 3.12 Å. The Mg(3)-Ga(1) bond length is 2.87 Å. There are two shorter (3.03 Å) and one longer (3.14 Å) Mg(3)-Ga(2) bond length. In the fourth Mg site, Mg(4) is bonded to one Mg(2), two equivalent Mg(3), two equivalent Mg(4), three equivalent Mg(1), two equivalent Ga(1), and two equivalent Ga(2) atoms to form distorted MgMg8Ga4 cuboctahedra that share corners with two equivalent Mg(1)Mg7Ga3 cuboctahedra, corners with six equivalent Mg(4)Mg8Ga4 cuboctahedra, edges with four equivalent Mg(2)Mg7Ga5 cuboctahedra, faces with two equivalent Mg(4)Mg8Ga4 cuboctahedra, faces with four equivalent Mg(2)Mg7Ga5 cuboctahedra, and faces with five equivalent Mg(1)Mg7Ga3 cuboctahedra. Both Mg(4)-Mg(4) bond lengths are 3.10 Å. Both Mg(4)-Ga(1) bond lengths are 3.14 Å. Both Mg(4)-Ga(2) bond lengths are 3.05 Å. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded in a 8-coordinate geometry to one Mg(3), two equivalent Mg(1), two equivalent Mg(4), and three equivalent Mg(2) atoms. In the second Ga site, Ga(2) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Mg(2), two equivalent Mg(4), and three equivalent Mg(3) atoms.