Mg23Pr6C crystallizes in the cubic Fm-3m space group. There are four inequivalent Mg sites. In the first Mg site, Mg(2) is bonded in a 13-coordinate geometry to one Mg(4), three equivalent Mg(1), three equivalent Mg(2), three equivalent Mg(3), and three equivalent Pr(1) atoms. In the second Mg site, Mg(3) is bonded to four equivalent Mg(1), four equivalent Mg(2), and four equivalent Pr(1) atoms to form MgPr4Mg8 cuboctahedra that share corners with four equivalent Mg(3)Pr4Mg8 cuboctahedra, corners with eight equivalent Mg(1)Pr3Mg9 cuboctahedra, edges with two equivalent C(1)Pr6 octahedra, faces with eight equivalent Mg(1)Pr3Mg9 cuboctahedra, and faces with eight equivalent Mg(3)Pr4Mg8 cuboctahedra. In the third Mg site, Mg(4) is bonded in a body-centered cubic geometry to eight equivalent Mg(2) atoms. In the fourth Mg site, Mg(1) is bonded to three equivalent Mg(1), three equivalent Mg(2), three equivalent Mg(3), and three equivalent Pr(1) atoms to form MgPr3Mg9 cuboctahedra that share corners with six equivalent Mg(1)Pr3Mg9 cuboctahedra, corners with six equivalent Mg(3)Pr4Mg8 cuboctahedra, faces with six equivalent Mg(1)Pr3Mg9 cuboctahedra, faces with six equivalent Mg(3)Pr4Mg8 cuboctahedra, and  a faceface with one C(1)Pr6 octahedra. Pr(1) is bonded in a single-bond geometry to four equivalent Mg(1), four equivalent Mg(2), four equivalent Mg(3), and one C(1) atom. C(1) is bonded to six equivalent Pr(1) atoms to form CPr6 octahedra that share edges with twelve equivalent Mg(3)Pr4Mg8 cuboctahedra and faces with eight equivalent Mg(1)Pr3Mg9 cuboctahedra.
Mg23Pr6C crystallizes in the cubic Fm-3m space group. There are four inequivalent Mg sites. In the first Mg site, Mg(2) is bonded in a 13-coordinate geometry to one Mg(4), three equivalent Mg(1), three equivalent Mg(2), three equivalent Mg(3), and three equivalent Pr(1) atoms. The Mg(2)-Mg(4) bond length is 3.02 Å. All Mg(2)-Mg(1) bond lengths are 3.17 Å. All Mg(2)-Mg(2) bond lengths are 3.48 Å. All Mg(2)-Mg(3) bond lengths are 3.15 Å. All Mg(2)-Pr(1) bond lengths are 3.72 Å. In the second Mg site, Mg(3) is bonded to four equivalent Mg(1), four equivalent Mg(2), and four equivalent Pr(1) atoms to form MgPr4Mg8 cuboctahedra that share corners with four equivalent Mg(3)Pr4Mg8 cuboctahedra, corners with eight equivalent Mg(1)Pr3Mg9 cuboctahedra, edges with two equivalent C(1)Pr6 octahedra, faces with eight equivalent Mg(1)Pr3Mg9 cuboctahedra, and faces with eight equivalent Mg(3)Pr4Mg8 cuboctahedra. All Mg(3)-Mg(1) bond lengths are 2.94 Å. All Mg(3)-Pr(1) bond lengths are 3.72 Å. In the third Mg site, Mg(4) is bonded in a body-centered cubic geometry to eight equivalent Mg(2) atoms. In the fourth Mg site, Mg(1) is bonded to three equivalent Mg(1), three equivalent Mg(2), three equivalent Mg(3), and three equivalent Pr(1) atoms to form MgPr3Mg9 cuboctahedra that share corners with six equivalent Mg(1)Pr3Mg9 cuboctahedra, corners with six equivalent Mg(3)Pr4Mg8 cuboctahedra, faces with six equivalent Mg(1)Pr3Mg9 cuboctahedra, faces with six equivalent Mg(3)Pr4Mg8 cuboctahedra, and  a faceface with one C(1)Pr6 octahedra. All Mg(1)-Mg(1) bond lengths are 3.22 Å. All Mg(1)-Pr(1) bond lengths are 3.49 Å. Pr(1) is bonded in a single-bond geometry to four equivalent Mg(1), four equivalent Mg(2), four equivalent Mg(3), and one C(1) atom. The Pr(1)-C(1) bond length is 2.67 Å. C(1) is bonded to six equivalent Pr(1) atoms to form CPr6 octahedra that share edges with twelve equivalent Mg(3)Pr4Mg8 cuboctahedra and faces with eight equivalent Mg(1)Pr3Mg9 cuboctahedra.