Ca2Mg crystallizes in the hexagonal P-6m2 space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to six equivalent Ca(1) and six equivalent Ca(2) atoms to form CaCa12 cuboctahedra that share corners with six equivalent Ca(1)Ca12 cuboctahedra, corners with twelve equivalent Ca(2)Ca3Mg3 cuboctahedra, edges with six equivalent Ca(1)Ca12 cuboctahedra, edges with twelve equivalent Ca(2)Ca3Mg3 cuboctahedra, and faces with six equivalent Ca(1)Ca12 cuboctahedra. In the second Ca site, Ca(2) is bonded to three equivalent Ca(1) and three equivalent Mg(1) atoms to form distorted CaCa3Mg3 cuboctahedra that share corners with six equivalent Ca(1)Ca12 cuboctahedra, corners with six equivalent Ca(2)Ca3Mg3 cuboctahedra, corners with six equivalent Ca(3)Mg6 cuboctahedra, edges with six equivalent Ca(1)Ca12 cuboctahedra, edges with six equivalent Ca(2)Ca3Mg3 cuboctahedra,  a faceface with one Ca(2)Ca3Mg3 cuboctahedra, and  a faceface with one Ca(3)Mg6 cuboctahedra. In the third Ca site, Ca(3) is bonded to six equivalent Mg(1) atoms to form distorted CaMg6 cuboctahedra that share corners with twelve equivalent Ca(2)Ca3Mg3 cuboctahedra, edges with six equivalent Ca(3)Mg6 cuboctahedra, and faces with two equivalent Ca(2)Ca3Mg3 cuboctahedra. Mg(1) is bonded in a 6-coordinate geometry to three equivalent Ca(2) and three equivalent Ca(3) atoms.
Ca2Mg crystallizes in the hexagonal P-6m2 space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to six equivalent Ca(1) and six equivalent Ca(2) atoms to form CaCa12 cuboctahedra that share corners with six equivalent Ca(1)Ca12 cuboctahedra, corners with twelve equivalent Ca(2)Ca3Mg3 cuboctahedra, edges with six equivalent Ca(1)Ca12 cuboctahedra, edges with twelve equivalent Ca(2)Ca3Mg3 cuboctahedra, and faces with six equivalent Ca(1)Ca12 cuboctahedra. All Ca(1)-Ca(1) bond lengths are 3.79 Å. All Ca(1)-Ca(2) bond lengths are 3.88 Å. In the second Ca site, Ca(2) is bonded to three equivalent Ca(1) and three equivalent Mg(1) atoms to form distorted CaCa3Mg3 cuboctahedra that share corners with six equivalent Ca(1)Ca12 cuboctahedra, corners with six equivalent Ca(2)Ca3Mg3 cuboctahedra, corners with six equivalent Ca(3)Mg6 cuboctahedra, edges with six equivalent Ca(1)Ca12 cuboctahedra, edges with six equivalent Ca(2)Ca3Mg3 cuboctahedra,  a faceface with one Ca(2)Ca3Mg3 cuboctahedra, and  a faceface with one Ca(3)Mg6 cuboctahedra. All Ca(2)-Mg(1) bond lengths are 3.50 Å. In the third Ca site, Ca(3) is bonded to six equivalent Mg(1) atoms to form distorted CaMg6 cuboctahedra that share corners with twelve equivalent Ca(2)Ca3Mg3 cuboctahedra, edges with six equivalent Ca(3)Mg6 cuboctahedra, and faces with two equivalent Ca(2)Ca3Mg3 cuboctahedra. All Ca(3)-Mg(1) bond lengths are 3.56 Å. Mg(1) is bonded in a 6-coordinate geometry to three equivalent Ca(2) and three equivalent Ca(3) atoms.