Mg2Ca crystallizes in the monoclinic Cm space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent Ca(1), two equivalent Ca(2), one Mg(3), two equivalent Mg(1), two equivalent Mg(4), and three equivalent Mg(2) atoms to form a mixture of distorted face and corner-sharing CaCa4Mg8 cuboctahedra. In the second Ca site, Ca(2) is bonded in a 12-coordinate geometry to two equivalent Ca(1), two equivalent Ca(2), one Mg(1), two equivalent Mg(2), two equivalent Mg(4), and three equivalent Mg(3) atoms. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 3-coordinate geometry to one Ca(2), two equivalent Ca(1), two equivalent Mg(2), two equivalent Mg(3), and two equivalent Mg(4) atoms. In the second Mg site, Mg(2) is bonded in a 10-coordinate geometry to two equivalent Ca(2), three equivalent Ca(1), one Mg(4), two equivalent Mg(1), and two equivalent Mg(2) atoms. In the third Mg site, Mg(3) is bonded in a 10-coordinate geometry to one Ca(1), three equivalent Ca(2), two equivalent Mg(1), two equivalent Mg(3), and two equivalent Mg(4) atoms. In the fourth Mg site, Mg(4) is bonded in a 11-coordinate geometry to two equivalent Ca(1), two equivalent Ca(2), one Mg(2), two equivalent Mg(1), two equivalent Mg(3), and two equivalent Mg(4) atoms.
Mg2Ca crystallizes in the monoclinic Cm space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent Ca(1), two equivalent Ca(2), one Mg(3), two equivalent Mg(1), two equivalent Mg(4), and three equivalent Mg(2) atoms to form a mixture of distorted face and corner-sharing CaCa4Mg8 cuboctahedra. Both Ca(1)-Ca(1) bond lengths are 3.45 Å. Both Ca(1)-Ca(2) bond lengths are 3.71 Å. The Ca(1)-Mg(3) bond length is 3.49 Å. Both Ca(1)-Mg(1) bond lengths are 3.37 Å. Both Ca(1)-Mg(4) bond lengths are 3.37 Å. There are two shorter (3.43 Å) and one longer (3.63 Å) Ca(1)-Mg(2) bond length. In the second Ca site, Ca(2) is bonded in a 12-coordinate geometry to two equivalent Ca(1), two equivalent Ca(2), one Mg(1), two equivalent Mg(2), two equivalent Mg(4), and three equivalent Mg(3) atoms. Both Ca(2)-Ca(2) bond lengths are 3.45 Å. The Ca(2)-Mg(1) bond length is 3.25 Å. Both Ca(2)-Mg(2) bond lengths are 3.43 Å. Both Ca(2)-Mg(4) bond lengths are 3.43 Å. There is one shorter (3.46 Å) and two longer (3.58 Å) Ca(2)-Mg(3) bond lengths. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 3-coordinate geometry to one Ca(2), two equivalent Ca(1), two equivalent Mg(2), two equivalent Mg(3), and two equivalent Mg(4) atoms. Both Mg(1)-Mg(2) bond lengths are 3.38 Å. Both Mg(1)-Mg(3) bond lengths are 3.51 Å. Both Mg(1)-Mg(4) bond lengths are 3.43 Å. In the second Mg site, Mg(2) is bonded in a 10-coordinate geometry to two equivalent Ca(2), three equivalent Ca(1), one Mg(4), two equivalent Mg(1), and two equivalent Mg(2) atoms. The Mg(2)-Mg(4) bond length is 3.22 Å. Both Mg(2)-Mg(2) bond lengths are 3.45 Å. In the third Mg site, Mg(3) is bonded in a 10-coordinate geometry to one Ca(1), three equivalent Ca(2), two equivalent Mg(1), two equivalent Mg(3), and two equivalent Mg(4) atoms. Both Mg(3)-Mg(3) bond lengths are 3.45 Å. Both Mg(3)-Mg(4) bond lengths are 3.28 Å. In the fourth Mg site, Mg(4) is bonded in a 11-coordinate geometry to two equivalent Ca(1), two equivalent Ca(2), one Mg(2), two equivalent Mg(1), two equivalent Mg(3), and two equivalent Mg(4) atoms. Both Mg(4)-Mg(4) bond lengths are 3.45 Å.