MgCa crystallizes in the orthorhombic Amm2 space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent Ca(2), three equivalent Ca(1), three equivalent Mg(1), and four equivalent Mg(2) atoms to form distorted CaCa5Mg7 cuboctahedra that share corners with nine equivalent Ca(1)Ca5Mg7 cuboctahedra; corners with nine equivalent Mg(1)Ca8Mg4 cuboctahedra; edges with four equivalent Ca(2)Ca4Mg8 cuboctahedra; edges with six equivalent Ca(1)Ca5Mg7 cuboctahedra; faces with three equivalent Mg(1)Ca8Mg4 cuboctahedra; faces with four equivalent Ca(2)Ca4Mg8 cuboctahedra; and faces with five Ca(1,1)Ca5Mg7 cuboctahedra. In the second Ca site, Ca(1) is bonded to two equivalent Ca(2), three equivalent Ca(1), three equivalent Mg(1), and four equivalent Mg(2) atoms to form distorted CaCa5Mg7 cuboctahedra that share corners with nine equivalent Ca(1)Ca5Mg7 cuboctahedra; corners with nine equivalent Mg(1)Ca8Mg4 cuboctahedra; edges with four equivalent Ca(2)Ca4Mg8 cuboctahedra; edges with six equivalent Ca(1)Ca5Mg7 cuboctahedra; faces with three equivalent Mg(1)Ca8Mg4 cuboctahedra; faces with four equivalent Ca(2)Ca4Mg8 cuboctahedra; and faces with five Ca(1,1)Ca5Mg7 cuboctahedra. In the third Ca site, Ca(2) is bonded to four Ca(1,1); two equivalent Mg(1); and six equivalent Mg(2) atoms to form distorted CaCa4Mg8 cuboctahedra that share edges with four equivalent Mg(1)Ca8Mg4 cuboctahedra; edges with six equivalent Ca(2)Ca4Mg8 cuboctahedra; edges with eight Ca(1,1)Ca5Mg7 cuboctahedra; faces with two equivalent Ca(2)Ca4Mg8 cuboctahedra; faces with four equivalent Mg(1)Ca8Mg4 cuboctahedra; and faces with eight Ca(1,1)Ca5Mg7 cuboctahedra. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Ca(2); six Ca(1,1); and four equivalent Mg(2) atoms to form distorted MgCa8Mg4 cuboctahedra that share corners with eighteen Ca(1,1)Ca5Mg7 cuboctahedra; edges with four equivalent Ca(2)Ca4Mg8 cuboctahedra; edges with six equivalent Mg(1)Ca8Mg4 cuboctahedra; faces with two equivalent Mg(1)Ca8Mg4 cuboctahedra; faces with four equivalent Ca(2)Ca4Mg8 cuboctahedra; and faces with six Ca(1,1)Ca5Mg7 cuboctahedra. In the second Mg site, Mg(2) is bonded in a 7-coordinate geometry to three equivalent Ca(2); four Ca(1,1); and two equivalent Mg(1) atoms.
MgCa crystallizes in the orthorhombic Amm2 space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent Ca(2), three equivalent Ca(1), three equivalent Mg(1), and four equivalent Mg(2) atoms to form distorted CaCa5Mg7 cuboctahedra that share corners with nine equivalent Ca(1)Ca5Mg7 cuboctahedra; corners with nine equivalent Mg(1)Ca8Mg4 cuboctahedra; edges with four equivalent Ca(2)Ca4Mg8 cuboctahedra; edges with six equivalent Ca(1)Ca5Mg7 cuboctahedra; faces with three equivalent Mg(1)Ca8Mg4 cuboctahedra; faces with four equivalent Ca(2)Ca4Mg8 cuboctahedra; and faces with five Ca(1,1)Ca5Mg7 cuboctahedra. Both Ca(1)-Ca(2) bond lengths are 3.62 Å. There are two shorter (3.47 Å) and one longer (3.75 Å) Ca(1)-Ca(1) bond length. There are two shorter (3.51 Å) and one longer (3.67 Å) Ca(1)-Mg(1) bond length. There are two shorter (3.49 Å) and two longer (3.51 Å) Ca(1)-Mg(2) bond lengths. In the second Ca site, Ca(1) is bonded to two equivalent Ca(2), three equivalent Ca(1), three equivalent Mg(1), and four equivalent Mg(2) atoms to form distorted CaCa5Mg7 cuboctahedra that share corners with nine equivalent Ca(1)Ca5Mg7 cuboctahedra; corners with nine equivalent Mg(1)Ca8Mg4 cuboctahedra; edges with four equivalent Ca(2)Ca4Mg8 cuboctahedra; edges with six equivalent Ca(1)Ca5Mg7 cuboctahedra; faces with three equivalent Mg(1)Ca8Mg4 cuboctahedra; faces with four equivalent Ca(2)Ca4Mg8 cuboctahedra; and faces with five Ca(1,1)Ca5Mg7 cuboctahedra. Both Ca(1)-Ca(2) bond lengths are 3.62 Å. There are two shorter (3.51 Å) and one longer (3.67 Å) Ca(1)-Mg(1) bond length. There are two shorter (3.49 Å) and two longer (3.51 Å) Ca(1)-Mg(2) bond lengths. In the third Ca site, Ca(2) is bonded to four Ca(1,1); two equivalent Mg(1); and six equivalent Mg(2) atoms to form distorted CaCa4Mg8 cuboctahedra that share edges with four equivalent Mg(1)Ca8Mg4 cuboctahedra; edges with six equivalent Ca(2)Ca4Mg8 cuboctahedra; edges with eight Ca(1,1)Ca5Mg7 cuboctahedra; faces with two equivalent Ca(2)Ca4Mg8 cuboctahedra; faces with four equivalent Mg(1)Ca8Mg4 cuboctahedra; and faces with eight Ca(1,1)Ca5Mg7 cuboctahedra. Both Ca(2)-Mg(1) bond lengths are 3.45 Å. There are a spread of Ca(2)-Mg(2) bond distances ranging from 3.38-3.66 Å. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Ca(2); six Ca(1,1); and four equivalent Mg(2) atoms to form distorted MgCa8Mg4 cuboctahedra that share corners with eighteen Ca(1,1)Ca5Mg7 cuboctahedra; edges with four equivalent Ca(2)Ca4Mg8 cuboctahedra; edges with six equivalent Mg(1)Ca8Mg4 cuboctahedra; faces with two equivalent Mg(1)Ca8Mg4 cuboctahedra; faces with four equivalent Ca(2)Ca4Mg8 cuboctahedra; and faces with six Ca(1,1)Ca5Mg7 cuboctahedra. All Mg(1)-Mg(2) bond lengths are 3.48 Å. In the second Mg site, Mg(2) is bonded in a 7-coordinate geometry to three equivalent Ca(2); four Ca(1,1); and two equivalent Mg(1) atoms.