Mg14CeSi crystallizes in the hexagonal P-6m2 space group. There are seven inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(4); four Mg(1,1); four Mg(3,3,3); and two equivalent Ce(1) atoms to form MgCe2Mg10 cuboctahedra that share corners with four equivalent Si(1)Mg12 cuboctahedra; corners with six equivalent Mg(1)Ce2Mg10 cuboctahedra; corners with eight equivalent Mg(2)Mg10Si2 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with four Mg(1,1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3,3)CeMg10Si cuboctahedra; faces with two equivalent Mg(2)Mg10Si2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with four Mg(1,1)Ce2Mg10 cuboctahedra; and faces with ten Mg(3,3,3)CeMg10Si cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Mg(4); four equivalent Mg(2); four Mg(3,3,3); and two equivalent Si(1) atoms to form distorted MgMg10Si2 cuboctahedra that share corners with four equivalent Ce(1)Mg12 cuboctahedra; corners with six equivalent Mg(2)Mg10Si2 cuboctahedra; corners with eight Mg(1,1)Ce2Mg10 cuboctahedra; edges with two equivalent Si(1)Mg12 cuboctahedra; edges with four equivalent Mg(2)Mg10Si2 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3,3)CeMg10Si cuboctahedra; faces with two equivalent Mg(1)Ce2Mg10 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Si(1)Mg12 cuboctahedra; faces with four equivalent Mg(2)Mg10Si2 cuboctahedra; and faces with ten Mg(3,3,3)CeMg10Si cuboctahedra. In the third Mg site, Mg(1) is bonded to two equivalent Mg(4), four equivalent Mg(1), four equivalent Mg(3), and two equivalent Ce(1) atoms to form MgCe2Mg10 cuboctahedra that share corners with four equivalent Si(1)Mg12 cuboctahedra; corners with six equivalent Mg(1)Ce2Mg10 cuboctahedra; corners with eight equivalent Mg(2)Mg10Si2 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight equivalent Mg(3)CeMg10Si cuboctahedra; faces with two equivalent Mg(2)Mg10Si2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with four equivalent Mg(1)Ce2Mg10 cuboctahedra; and faces with ten Mg(3,3,3)CeMg10Si cuboctahedra. In the fourth Mg site, Mg(3) is bonded to two Mg(1,1); two equivalent Mg(2); two equivalent Mg(4); four Mg(3,3); one Ce(1); and one Si(1) atom to form distorted MgCeMg10Si cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)CeMg10Si cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with two equivalent Si(1)Mg12 cuboctahedra; edges with four Mg(1,1)Ce2Mg10 cuboctahedra; edges with four Mg(3,3)CeMg10Si cuboctahedra; edges with four equivalent Mg(2)Mg10Si2 cuboctahedra;  a faceface with one Ce(1)Mg12 cuboctahedra;  a faceface with one Si(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five Mg(1,1)Ce2Mg10 cuboctahedra; faces with five equivalent Mg(2)Mg10Si2 cuboctahedra; and faces with six Mg(3,3)CeMg10Si cuboctahedra. In the fifth Mg site, Mg(3) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), four equivalent Mg(3), one Ce(1), and one Si(1) atom to form distorted MgCeMg10Si cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)CeMg10Si cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with two equivalent Si(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(3)CeMg10Si cuboctahedra; edges with four equivalent Mg(2)Mg10Si2 cuboctahedra;  a faceface with one Ce(1)Mg12 cuboctahedra;  a faceface with one Si(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five Mg(1,1)Ce2Mg10 cuboctahedra; faces with five equivalent Mg(2)Mg10Si2 cuboctahedra; and faces with six Mg(3,3)CeMg10Si cuboctahedra. In the sixth Mg site, Mg(3) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), four equivalent Mg(3), one Ce(1), and one Si(1) atom to form distorted MgCeMg10Si cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)CeMg10Si cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with two equivalent Si(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(3)CeMg10Si cuboctahedra; edges with four equivalent Mg(2)Mg10Si2 cuboctahedra;  a faceface with one Ce(1)Mg12 cuboctahedra;  a faceface with one Si(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five Mg(1,1)Ce2Mg10 cuboctahedra; faces with five equivalent Mg(2)Mg10Si2 cuboctahedra; and faces with six Mg(3,3)CeMg10Si cuboctahedra. In the seventh Mg site, Mg(4) is bonded to three Mg(1,1); three equivalent Mg(2); and six Mg(3,3) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(4)Mg12 cuboctahedra; corners with twelve Mg(3,3)CeMg10Si cuboctahedra; edges with six Mg(1,1)Ce2Mg10 cuboctahedra; edges with six Mg(3,3)CeMg10Si cuboctahedra; edges with six equivalent Mg(2)Mg10Si2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with three Mg(1,1)Ce2Mg10 cuboctahedra; faces with three equivalent Mg(2)Mg10Si2 cuboctahedra; faces with three equivalent Ce(1)Mg12 cuboctahedra; faces with three equivalent Si(1)Mg12 cuboctahedra; and faces with six Mg(3,3)CeMg10Si cuboctahedra. Ce(1) is bonded to six Mg(1,1) and six Mg(3,3,3) atoms to form CeMg12 cuboctahedra that share corners with six equivalent Ce(1)Mg12 cuboctahedra; corners with twelve equivalent Mg(2)Mg10Si2 cuboctahedra; edges with six Mg(1,1)Ce2Mg10 cuboctahedra; edges with twelve Mg(3,3,3)CeMg10Si cuboctahedra; faces with two equivalent Si(1)Mg12 cuboctahedra; faces with six Mg(1,1)Ce2Mg10 cuboctahedra; faces with six Mg(3,3,3)CeMg10Si cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra. Si(1) is bonded to six equivalent Mg(2) and six Mg(3,3,3) atoms to form SiMg12 cuboctahedra that share corners with six equivalent Si(1)Mg12 cuboctahedra; corners with twelve Mg(1,1)Ce2Mg10 cuboctahedra; edges with six equivalent Mg(2)Mg10Si2 cuboctahedra; edges with twelve Mg(3,3,3)CeMg10Si cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with six Mg(3,3,3)CeMg10Si cuboctahedra; faces with six equivalent Mg(2)Mg10Si2 cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra.
Mg14CeSi crystallizes in the hexagonal P-6m2 space group. There are seven inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(4); four Mg(1,1); four Mg(3,3,3); and two equivalent Ce(1) atoms to form MgCe2Mg10 cuboctahedra that share corners with four equivalent Si(1)Mg12 cuboctahedra; corners with six equivalent Mg(1)Ce2Mg10 cuboctahedra; corners with eight equivalent Mg(2)Mg10Si2 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with four Mg(1,1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3,3)CeMg10Si cuboctahedra; faces with two equivalent Mg(2)Mg10Si2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with four Mg(1,1)Ce2Mg10 cuboctahedra; and faces with ten Mg(3,3,3)CeMg10Si cuboctahedra. Both Mg(1)-Mg(4) bond lengths are 3.16 Å. There are two shorter (3.11 Å) and two longer (3.26 Å) Mg(1)-Mg(1,1) bond lengths. All Mg(1)-Mg(3,3,3) bond lengths are 3.23 Å. Both Mg(1)-Ce(1) bond lengths are 3.18 Å. In the second Mg site, Mg(2) is bonded to two equivalent Mg(4); four equivalent Mg(2); four Mg(3,3,3); and two equivalent Si(1) atoms to form distorted MgMg10Si2 cuboctahedra that share corners with four equivalent Ce(1)Mg12 cuboctahedra; corners with six equivalent Mg(2)Mg10Si2 cuboctahedra; corners with eight Mg(1,1)Ce2Mg10 cuboctahedra; edges with two equivalent Si(1)Mg12 cuboctahedra; edges with four equivalent Mg(2)Mg10Si2 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3,3)CeMg10Si cuboctahedra; faces with two equivalent Mg(1)Ce2Mg10 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Si(1)Mg12 cuboctahedra; faces with four equivalent Mg(2)Mg10Si2 cuboctahedra; and faces with ten Mg(3,3,3)CeMg10Si cuboctahedra. Both Mg(2)-Mg(4) bond lengths are 3.23 Å. There are two shorter (3.16 Å) and two longer (3.21 Å) Mg(2)-Mg(2) bond lengths. All Mg(2)-Mg(3,3,3) bond lengths are 3.14 Å. Both Mg(2)-Si(1) bond lengths are 3.18 Å. In the third Mg site, Mg(1) is bonded to two equivalent Mg(4), four equivalent Mg(1), four equivalent Mg(3), and two equivalent Ce(1) atoms to form MgCe2Mg10 cuboctahedra that share corners with four equivalent Si(1)Mg12 cuboctahedra; corners with six equivalent Mg(1)Ce2Mg10 cuboctahedra; corners with eight equivalent Mg(2)Mg10Si2 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight equivalent Mg(3)CeMg10Si cuboctahedra; faces with two equivalent Mg(2)Mg10Si2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with four equivalent Mg(1)Ce2Mg10 cuboctahedra; and faces with ten Mg(3,3,3)CeMg10Si cuboctahedra. Both Mg(1)-Mg(4) bond lengths are 3.16 Å. All Mg(1)-Mg(3) bond lengths are 3.23 Å. Both Mg(1)-Ce(1) bond lengths are 3.18 Å. In the fourth Mg site, Mg(3) is bonded to two Mg(1,1); two equivalent Mg(2); two equivalent Mg(4); four Mg(3,3); one Ce(1); and one Si(1) atom to form distorted MgCeMg10Si cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)CeMg10Si cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with two equivalent Si(1)Mg12 cuboctahedra; edges with four Mg(1,1)Ce2Mg10 cuboctahedra; edges with four Mg(3,3)CeMg10Si cuboctahedra; edges with four equivalent Mg(2)Mg10Si2 cuboctahedra;  a faceface with one Ce(1)Mg12 cuboctahedra;  a faceface with one Si(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five Mg(1,1)Ce2Mg10 cuboctahedra; faces with five equivalent Mg(2)Mg10Si2 cuboctahedra; and faces with six Mg(3,3)CeMg10Si cuboctahedra. Both Mg(3)-Mg(4) bond lengths are 3.19 Å. There are two shorter (3.15 Å) and two longer (3.22 Å) Mg(3)-Mg(3,3) bond lengths. The Mg(3)-Ce(1) bond length is 3.23 Å. The Mg(3)-Si(1) bond length is 3.12 Å. In the fifth Mg site, Mg(3) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), four equivalent Mg(3), one Ce(1), and one Si(1) atom to form distorted MgCeMg10Si cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)CeMg10Si cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with two equivalent Si(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(3)CeMg10Si cuboctahedra; edges with four equivalent Mg(2)Mg10Si2 cuboctahedra;  a faceface with one Ce(1)Mg12 cuboctahedra;  a faceface with one Si(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five Mg(1,1)Ce2Mg10 cuboctahedra; faces with five equivalent Mg(2)Mg10Si2 cuboctahedra; and faces with six Mg(3,3)CeMg10Si cuboctahedra. Both Mg(3)-Mg(4) bond lengths are 3.19 Å. The Mg(3)-Ce(1) bond length is 3.23 Å. The Mg(3)-Si(1) bond length is 3.12 Å. In the sixth Mg site, Mg(3) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), four equivalent Mg(3), one Ce(1), and one Si(1) atom to form distorted MgCeMg10Si cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)CeMg10Si cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with two equivalent Si(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(3)CeMg10Si cuboctahedra; edges with four equivalent Mg(2)Mg10Si2 cuboctahedra;  a faceface with one Ce(1)Mg12 cuboctahedra;  a faceface with one Si(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five Mg(1,1)Ce2Mg10 cuboctahedra; faces with five equivalent Mg(2)Mg10Si2 cuboctahedra; and faces with six Mg(3,3)CeMg10Si cuboctahedra. Both Mg(3)-Mg(4) bond lengths are 3.19 Å. There are two shorter (3.15 Å) and two longer (3.22 Å) Mg(3)-Mg(3) bond lengths. The Mg(3)-Ce(1) bond length is 3.23 Å. The Mg(3)-Si(1) bond length is 3.12 Å. In the seventh Mg site, Mg(4) is bonded to three Mg(1,1); three equivalent Mg(2); and six Mg(3,3) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(4)Mg12 cuboctahedra; corners with twelve Mg(3,3)CeMg10Si cuboctahedra; edges with six Mg(1,1)Ce2Mg10 cuboctahedra; edges with six Mg(3,3)CeMg10Si cuboctahedra; edges with six equivalent Mg(2)Mg10Si2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with three Mg(1,1)Ce2Mg10 cuboctahedra; faces with three equivalent Mg(2)Mg10Si2 cuboctahedra; faces with three equivalent Ce(1)Mg12 cuboctahedra; faces with three equivalent Si(1)Mg12 cuboctahedra; and faces with six Mg(3,3)CeMg10Si cuboctahedra. Ce(1) is bonded to six Mg(1,1) and six Mg(3,3,3) atoms to form CeMg12 cuboctahedra that share corners with six equivalent Ce(1)Mg12 cuboctahedra; corners with twelve equivalent Mg(2)Mg10Si2 cuboctahedra; edges with six Mg(1,1)Ce2Mg10 cuboctahedra; edges with twelve Mg(3,3,3)CeMg10Si cuboctahedra; faces with two equivalent Si(1)Mg12 cuboctahedra; faces with six Mg(1,1)Ce2Mg10 cuboctahedra; faces with six Mg(3,3,3)CeMg10Si cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra. Si(1) is bonded to six equivalent Mg(2) and six Mg(3,3,3) atoms to form SiMg12 cuboctahedra that share corners with six equivalent Si(1)Mg12 cuboctahedra; corners with twelve Mg(1,1)Ce2Mg10 cuboctahedra; edges with six equivalent Mg(2)Mg10Si2 cuboctahedra; edges with twelve Mg(3,3,3)CeMg10Si cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with six Mg(3,3,3)CeMg10Si cuboctahedra; faces with six equivalent Mg(2)Mg10Si2 cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra.