SrMg6Hf crystallizes in the orthorhombic Amm2 space group. Sr(1) is bonded to two equivalent Mg(2), four equivalent Mg(1), four equivalent Mg(3), and two equivalent Hf(1) atoms to form SrHf2Mg10 cuboctahedra that share corners with four equivalent Mg(2)Sr2Mg10 cuboctahedra, corners with six equivalent Sr(1)Hf2Mg10 cuboctahedra, edges with two equivalent Mg(2)Sr2Mg10 cuboctahedra, edges with four equivalent Hf(1)Sr2Mg10 cuboctahedra, edges with eight equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, faces with two equivalent Sr(1)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with two equivalent Hf(1)Sr2Mg10 cuboctahedra, faces with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, and faces with six equivalent Mg(4)Hf2Mg10 cuboctahedra. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 12-coordinate geometry to two equivalent Sr(1), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), and two equivalent Hf(1) atoms. In the second Mg site, Mg(2) is bonded to two equivalent Sr(1), two equivalent Mg(4), four equivalent Mg(1), and four equivalent Mg(3) atoms to form distorted MgSr2Mg10 cuboctahedra that share corners with four equivalent Sr(1)Hf2Mg10 cuboctahedra, corners with six equivalent Mg(2)Sr2Mg10 cuboctahedra, edges with two equivalent Sr(1)Hf2Mg10 cuboctahedra, edges with four equivalent Mg(4)Hf2Mg10 cuboctahedra, edges with eight equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, faces with two equivalent Sr(1)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(4)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, and faces with six equivalent Hf(1)Sr2Mg10 cuboctahedra. In the third Mg site, Mg(3) is bonded to two equivalent Sr(1), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), and two equivalent Hf(1) atoms to form distorted MgSr2Hf2Mg8 cuboctahedra that share corners with four equivalent Mg(4)Hf2Mg10 cuboctahedra, corners with four equivalent Hf(1)Sr2Mg10 cuboctahedra, corners with ten equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, edges with two equivalent Mg(4)Hf2Mg10 cuboctahedra, edges with two equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, edges with two equivalent Hf(1)Sr2Mg10 cuboctahedra, edges with four equivalent Sr(1)Hf2Mg10 cuboctahedra, edges with four equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with two equivalent Sr(1)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(4)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with two equivalent Hf(1)Sr2Mg10 cuboctahedra, and faces with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra. In the fourth Mg site, Mg(4) is bonded to two equivalent Mg(2), four equivalent Mg(1), four equivalent Mg(3), and two equivalent Hf(1) atoms to form MgHf2Mg10 cuboctahedra that share corners with four equivalent Hf(1)Sr2Mg10 cuboctahedra, corners with six equivalent Mg(4)Hf2Mg10 cuboctahedra, corners with eight equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, edges with two equivalent Hf(1)Sr2Mg10 cuboctahedra, edges with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, edges with four equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with two equivalent Mg(4)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with two equivalent Hf(1)Sr2Mg10 cuboctahedra, faces with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, and faces with six equivalent Sr(1)Hf2Mg10 cuboctahedra. Hf(1) is bonded to two equivalent Sr(1), two equivalent Mg(4), four equivalent Mg(1), and four equivalent Mg(3) atoms to form HfSr2Mg10 cuboctahedra that share corners with four equivalent Mg(4)Hf2Mg10 cuboctahedra, corners with six equivalent Hf(1)Sr2Mg10 cuboctahedra, corners with eight equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, edges with two equivalent Mg(4)Hf2Mg10 cuboctahedra, edges with four equivalent Sr(1)Hf2Mg10 cuboctahedra, edges with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, faces with two equivalent Sr(1)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(4)Hf2Mg10 cuboctahedra, faces with two equivalent Hf(1)Sr2Mg10 cuboctahedra, faces with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, and faces with six equivalent Mg(2)Sr2Mg10 cuboctahedra.
SrMg6Hf crystallizes in the orthorhombic Amm2 space group. Sr(1) is bonded to two equivalent Mg(2), four equivalent Mg(1), four equivalent Mg(3), and two equivalent Hf(1) atoms to form SrHf2Mg10 cuboctahedra that share corners with four equivalent Mg(2)Sr2Mg10 cuboctahedra, corners with six equivalent Sr(1)Hf2Mg10 cuboctahedra, edges with two equivalent Mg(2)Sr2Mg10 cuboctahedra, edges with four equivalent Hf(1)Sr2Mg10 cuboctahedra, edges with eight equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, faces with two equivalent Sr(1)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with two equivalent Hf(1)Sr2Mg10 cuboctahedra, faces with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, and faces with six equivalent Mg(4)Hf2Mg10 cuboctahedra. Both Sr(1)-Mg(2) bond lengths are 3.33 Å. There are two shorter (3.28 Å) and two longer (3.38 Å) Sr(1)-Mg(1) bond lengths. All Sr(1)-Mg(3) bond lengths are 3.32 Å. Both Sr(1)-Hf(1) bond lengths are 3.37 Å. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 12-coordinate geometry to two equivalent Sr(1), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), and two equivalent Hf(1) atoms. There is one shorter (3.16 Å) and one longer (3.49 Å) Mg(1)-Mg(1) bond length. There is one shorter (3.31 Å) and one longer (3.35 Å) Mg(1)-Mg(2) bond length. Both Mg(1)-Mg(3) bond lengths are 3.29 Å. Both Mg(1)-Mg(4) bond lengths are 3.32 Å. Both Mg(1)-Hf(1) bond lengths are 3.21 Å. In the second Mg site, Mg(2) is bonded to two equivalent Sr(1), two equivalent Mg(4), four equivalent Mg(1), and four equivalent Mg(3) atoms to form distorted MgSr2Mg10 cuboctahedra that share corners with four equivalent Sr(1)Hf2Mg10 cuboctahedra, corners with six equivalent Mg(2)Sr2Mg10 cuboctahedra, edges with two equivalent Sr(1)Hf2Mg10 cuboctahedra, edges with four equivalent Mg(4)Hf2Mg10 cuboctahedra, edges with eight equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, faces with two equivalent Sr(1)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(4)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, and faces with six equivalent Hf(1)Sr2Mg10 cuboctahedra. Both Mg(2)-Mg(4) bond lengths are 3.30 Å. All Mg(2)-Mg(3) bond lengths are 3.27 Å. In the third Mg site, Mg(3) is bonded to two equivalent Sr(1), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), and two equivalent Hf(1) atoms to form distorted MgSr2Hf2Mg8 cuboctahedra that share corners with four equivalent Mg(4)Hf2Mg10 cuboctahedra, corners with four equivalent Hf(1)Sr2Mg10 cuboctahedra, corners with ten equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, edges with two equivalent Mg(4)Hf2Mg10 cuboctahedra, edges with two equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, edges with two equivalent Hf(1)Sr2Mg10 cuboctahedra, edges with four equivalent Sr(1)Hf2Mg10 cuboctahedra, edges with four equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with two equivalent Sr(1)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(4)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with two equivalent Hf(1)Sr2Mg10 cuboctahedra, and faces with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra. There is one shorter (3.24 Å) and one longer (3.41 Å) Mg(3)-Mg(3) bond length. There is one shorter (3.31 Å) and one longer (3.35 Å) Mg(3)-Mg(4) bond length. There is one shorter (3.17 Å) and one longer (3.48 Å) Mg(3)-Hf(1) bond length. In the fourth Mg site, Mg(4) is bonded to two equivalent Mg(2), four equivalent Mg(1), four equivalent Mg(3), and two equivalent Hf(1) atoms to form MgHf2Mg10 cuboctahedra that share corners with four equivalent Hf(1)Sr2Mg10 cuboctahedra, corners with six equivalent Mg(4)Hf2Mg10 cuboctahedra, corners with eight equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, edges with two equivalent Hf(1)Sr2Mg10 cuboctahedra, edges with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, edges with four equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with two equivalent Mg(4)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(2)Sr2Mg10 cuboctahedra, faces with two equivalent Hf(1)Sr2Mg10 cuboctahedra, faces with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, and faces with six equivalent Sr(1)Hf2Mg10 cuboctahedra. Both Mg(4)-Hf(1) bond lengths are 3.33 Å. Hf(1) is bonded to two equivalent Sr(1), two equivalent Mg(4), four equivalent Mg(1), and four equivalent Mg(3) atoms to form HfSr2Mg10 cuboctahedra that share corners with four equivalent Mg(4)Hf2Mg10 cuboctahedra, corners with six equivalent Hf(1)Sr2Mg10 cuboctahedra, corners with eight equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, edges with two equivalent Mg(4)Hf2Mg10 cuboctahedra, edges with four equivalent Sr(1)Hf2Mg10 cuboctahedra, edges with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, faces with two equivalent Sr(1)Hf2Mg10 cuboctahedra, faces with two equivalent Mg(4)Hf2Mg10 cuboctahedra, faces with two equivalent Hf(1)Sr2Mg10 cuboctahedra, faces with four equivalent Mg(3)Sr2Hf2Mg8 cuboctahedra, and faces with six equivalent Mg(2)Sr2Mg10 cuboctahedra.