Mg14CeSi crystallizes in the orthorhombic Amm2 space group. There are seven inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(2), two equivalent Mg(6), four equivalent Mg(4), and four equivalent Mg(5) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(1)Mg12 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with four equivalent Mg(6)CeMg11 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, edges with eight equivalent Mg(5)CeMg10Si cuboctahedra, faces with two equivalent Mg(6)CeMg11 cuboctahedra, faces with two equivalent Mg(2)Mg12 cuboctahedra, faces with two equivalent Ce(1)Mg10Si2 cuboctahedra, faces with four equivalent Mg(5)CeMg10Si cuboctahedra, and faces with four equivalent Mg(4)Mg12 cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Mg(1), two equivalent Mg(7), four equivalent Mg(4), and four equivalent Mg(5) atoms to form MgMg12 cuboctahedra that share corners with four equivalent Ce(1)Mg10Si2 cuboctahedra, corners with six equivalent Mg(2)Mg12 cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, edges with eight equivalent Mg(5)CeMg10Si cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with four equivalent Mg(5)CeMg10Si cuboctahedra, faces with four equivalent Mg(4)Mg12 cuboctahedra, and faces with six equivalent Mg(6)CeMg11 cuboctahedra. In the third Mg site, Mg(3) is bonded in a 11-coordinate geometry to two equivalent Mg(3), two equivalent Mg(5), two equivalent Mg(6), two equivalent Mg(7), two equivalent Ce(1), and one Si(1) atom. In the fourth Mg site, Mg(4) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(5), two equivalent Mg(6), and two equivalent Mg(7) atoms to form MgMg12 cuboctahedra that share corners with four equivalent Ce(1)Mg10Si2 cuboctahedra, corners with six equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with two equivalent Mg(4)Mg12 cuboctahedra, edges with four equivalent Mg(5)CeMg10Si cuboctahedra, edges with four equivalent Mg(6)CeMg11 cuboctahedra, faces with two equivalent Mg(6)CeMg11 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Mg(2)Mg12 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, and faces with eight equivalent Mg(5)CeMg10Si cuboctahedra. In the fifth Mg site, Mg(5) is bonded to one Mg(1), one Mg(2), one Mg(3), one Mg(4), two equivalent Mg(5), two equivalent Mg(6), two equivalent Mg(7), one Ce(1), and one Si(1) atom to form distorted MgCeMg10Si cuboctahedra that share corners with four equivalent Mg(6)CeMg11 cuboctahedra, corners with ten equivalent Mg(5)CeMg10Si cuboctahedra, edges with two equivalent Mg(5)CeMg10Si cuboctahedra, edges with two equivalent Mg(6)CeMg11 cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with two equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent Ce(1)Mg10Si2 cuboctahedra,  a faceface with one Mg(1)Mg12 cuboctahedra,  a faceface with one Mg(2)Mg12 cuboctahedra,  a faceface with one Ce(1)Mg10Si2 cuboctahedra, faces with two equivalent Mg(6)CeMg11 cuboctahedra, faces with four equivalent Mg(5)CeMg10Si cuboctahedra, and faces with four equivalent Mg(4)Mg12 cuboctahedra. In the sixth Mg site, Mg(6) is bonded to one Mg(1), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(7), four equivalent Mg(5), and one Ce(1) atom to form distorted MgCeMg11 cuboctahedra that share corners with six equivalent Mg(6)CeMg11 cuboctahedra, corners with eight equivalent Mg(5)CeMg10Si cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with two equivalent Ce(1)Mg10Si2 cuboctahedra, edges with four equivalent Mg(5)CeMg10Si cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra,  a faceface with one Mg(1)Mg12 cuboctahedra,  a faceface with one Ce(1)Mg10Si2 cuboctahedra, faces with two equivalent Mg(6)CeMg11 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with three equivalent Mg(2)Mg12 cuboctahedra, and faces with four equivalent Mg(5)CeMg10Si cuboctahedra. In the seventh Mg site, Mg(7) is bonded in a distorted single-bond geometry to one Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(6), four equivalent Mg(5), and one Si(1) atom. Ce(1) is bonded to two equivalent Mg(6), four equivalent Mg(3), four equivalent Mg(5), and two equivalent Si(1) atoms to form CeMg10Si2 cuboctahedra that share corners with four equivalent Mg(2)Mg12 cuboctahedra, corners with six equivalent Ce(1)Mg10Si2 cuboctahedra, corners with eight equivalent Mg(4)Mg12 cuboctahedra, edges with four equivalent Mg(6)CeMg11 cuboctahedra, edges with eight equivalent Mg(5)CeMg10Si cuboctahedra, faces with two equivalent Mg(6)CeMg11 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, and faces with four equivalent Mg(5)CeMg10Si cuboctahedra. Si(1) is bonded in a 10-coordinate geometry to two equivalent Mg(3), two equivalent Mg(7), four equivalent Mg(5), and two equivalent Ce(1) atoms.
Mg14CeSi crystallizes in the orthorhombic Amm2 space group. There are seven inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(2), two equivalent Mg(6), four equivalent Mg(4), and four equivalent Mg(5) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(1)Mg12 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with four equivalent Mg(6)CeMg11 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, edges with eight equivalent Mg(5)CeMg10Si cuboctahedra, faces with two equivalent Mg(6)CeMg11 cuboctahedra, faces with two equivalent Mg(2)Mg12 cuboctahedra, faces with two equivalent Ce(1)Mg10Si2 cuboctahedra, faces with four equivalent Mg(5)CeMg10Si cuboctahedra, and faces with four equivalent Mg(4)Mg12 cuboctahedra. Both Mg(1)-Mg(2) bond lengths are 3.14 Å. Both Mg(1)-Mg(6) bond lengths are 3.13 Å. There are two shorter (3.24 Å) and two longer (3.27 Å) Mg(1)-Mg(4) bond lengths. All Mg(1)-Mg(5) bond lengths are 3.16 Å. In the second Mg site, Mg(2) is bonded to two equivalent Mg(1), two equivalent Mg(7), four equivalent Mg(4), and four equivalent Mg(5) atoms to form MgMg12 cuboctahedra that share corners with four equivalent Ce(1)Mg10Si2 cuboctahedra, corners with six equivalent Mg(2)Mg12 cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, edges with eight equivalent Mg(5)CeMg10Si cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with four equivalent Mg(5)CeMg10Si cuboctahedra, faces with four equivalent Mg(4)Mg12 cuboctahedra, and faces with six equivalent Mg(6)CeMg11 cuboctahedra. Both Mg(2)-Mg(7) bond lengths are 3.27 Å. There are two shorter (3.22 Å) and two longer (3.29 Å) Mg(2)-Mg(4) bond lengths. All Mg(2)-Mg(5) bond lengths are 3.14 Å. In the third Mg site, Mg(3) is bonded in a 11-coordinate geometry to two equivalent Mg(3), two equivalent Mg(5), two equivalent Mg(6), two equivalent Mg(7), two equivalent Ce(1), and one Si(1) atom. There is one shorter (3.03 Å) and one longer (3.25 Å) Mg(3)-Mg(3) bond length. Both Mg(3)-Mg(5) bond lengths are 3.16 Å. Both Mg(3)-Mg(6) bond lengths are 3.25 Å. Both Mg(3)-Mg(7) bond lengths are 3.13 Å. There is one shorter (3.25 Å) and one longer (3.26 Å) Mg(3)-Ce(1) bond length. The Mg(3)-Si(1) bond length is 3.03 Å. In the fourth Mg site, Mg(4) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(5), two equivalent Mg(6), and two equivalent Mg(7) atoms to form MgMg12 cuboctahedra that share corners with four equivalent Ce(1)Mg10Si2 cuboctahedra, corners with six equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with two equivalent Mg(4)Mg12 cuboctahedra, edges with four equivalent Mg(5)CeMg10Si cuboctahedra, edges with four equivalent Mg(6)CeMg11 cuboctahedra, faces with two equivalent Mg(6)CeMg11 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Mg(2)Mg12 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, and faces with eight equivalent Mg(5)CeMg10Si cuboctahedra. There is one shorter (3.09 Å) and one longer (3.19 Å) Mg(4)-Mg(4) bond length. Both Mg(4)-Mg(5) bond lengths are 3.15 Å. Both Mg(4)-Mg(6) bond lengths are 3.10 Å. Both Mg(4)-Mg(7) bond lengths are 3.32 Å. In the fifth Mg site, Mg(5) is bonded to one Mg(1), one Mg(2), one Mg(3), one Mg(4), two equivalent Mg(5), two equivalent Mg(6), two equivalent Mg(7), one Ce(1), and one Si(1) atom to form distorted MgCeMg10Si cuboctahedra that share corners with four equivalent Mg(6)CeMg11 cuboctahedra, corners with ten equivalent Mg(5)CeMg10Si cuboctahedra, edges with two equivalent Mg(5)CeMg10Si cuboctahedra, edges with two equivalent Mg(6)CeMg11 cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with two equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent Ce(1)Mg10Si2 cuboctahedra,  a faceface with one Mg(1)Mg12 cuboctahedra,  a faceface with one Mg(2)Mg12 cuboctahedra,  a faceface with one Ce(1)Mg10Si2 cuboctahedra, faces with two equivalent Mg(6)CeMg11 cuboctahedra, faces with four equivalent Mg(5)CeMg10Si cuboctahedra, and faces with four equivalent Mg(4)Mg12 cuboctahedra. There is one shorter (3.09 Å) and one longer (3.19 Å) Mg(5)-Mg(5) bond length. There is one shorter (3.21 Å) and one longer (3.30 Å) Mg(5)-Mg(6) bond length. There is one shorter (3.20 Å) and one longer (3.32 Å) Mg(5)-Mg(7) bond length. The Mg(5)-Ce(1) bond length is 3.24 Å. The Mg(5)-Si(1) bond length is 3.16 Å. In the sixth Mg site, Mg(6) is bonded to one Mg(1), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(7), four equivalent Mg(5), and one Ce(1) atom to form distorted MgCeMg11 cuboctahedra that share corners with six equivalent Mg(6)CeMg11 cuboctahedra, corners with eight equivalent Mg(5)CeMg10Si cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with two equivalent Ce(1)Mg10Si2 cuboctahedra, edges with four equivalent Mg(5)CeMg10Si cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra,  a faceface with one Mg(1)Mg12 cuboctahedra,  a faceface with one Ce(1)Mg10Si2 cuboctahedra, faces with two equivalent Mg(6)CeMg11 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with three equivalent Mg(2)Mg12 cuboctahedra, and faces with four equivalent Mg(5)CeMg10Si cuboctahedra. Both Mg(6)-Mg(7) bond lengths are 3.15 Å. The Mg(6)-Ce(1) bond length is 3.24 Å. In the seventh Mg site, Mg(7) is bonded in a distorted single-bond geometry to one Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(6), four equivalent Mg(5), and one Si(1) atom. The Mg(7)-Si(1) bond length is 3.10 Å. Ce(1) is bonded to two equivalent Mg(6), four equivalent Mg(3), four equivalent Mg(5), and two equivalent Si(1) atoms to form CeMg10Si2 cuboctahedra that share corners with four equivalent Mg(2)Mg12 cuboctahedra, corners with six equivalent Ce(1)Mg10Si2 cuboctahedra, corners with eight equivalent Mg(4)Mg12 cuboctahedra, edges with four equivalent Mg(6)CeMg11 cuboctahedra, edges with eight equivalent Mg(5)CeMg10Si cuboctahedra, faces with two equivalent Mg(6)CeMg11 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, and faces with four equivalent Mg(5)CeMg10Si cuboctahedra. Both Ce(1)-Si(1) bond lengths are 3.15 Å. Si(1) is bonded in a 10-coordinate geometry to two equivalent Mg(3), two equivalent Mg(7), four equivalent Mg(5), and two equivalent Ce(1) atoms.