MgTm5 crystallizes in the orthorhombic Amm2 space group. Mg(1) is bonded to two equivalent Tm(3), two equivalent Tm(4), two equivalent Tm(5), and four equivalent Tm(2) atoms to form distorted MgTm10 cuboctahedra that share corners with four equivalent Mg(1)Tm10 cuboctahedra, corners with four equivalent Tm(2)Tm8Mg4 cuboctahedra, corners with eight equivalent Tm(4)Tm10Mg2 cuboctahedra, corners with eight equivalent Tm(5)Tm10Mg2 cuboctahedra,  an edgeedge with one Tm(4)Tm10Mg2 cuboctahedra,  an edgeedge with one Tm(5)Tm10Mg2 cuboctahedra, edges with eight equivalent Tm(1)Tm12 cuboctahedra, faces with two equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(5)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(1)Tm12 cuboctahedra, faces with four equivalent Mg(1)Tm10 cuboctahedra, faces with four equivalent Tm(2)Tm8Mg4 cuboctahedra, and faces with six equivalent Tm(3)Tm10Mg2 cuboctahedra. There are five inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to two equivalent Tm(1), two equivalent Tm(2), two equivalent Tm(3), two equivalent Tm(5), and four equivalent Tm(4) atoms to form TmTm12 cuboctahedra that share corners with six equivalent Tm(3)Tm10Mg2 cuboctahedra, corners with six equivalent Tm(1)Tm12 cuboctahedra, corners with six equivalent Tm(2)Tm8Mg4 cuboctahedra, edges with three equivalent Tm(3)Tm10Mg2 cuboctahedra, edges with three equivalent Tm(2)Tm8Mg4 cuboctahedra, edges with four equivalent Tm(4)Tm10Mg2 cuboctahedra, edges with eight equivalent Mg(1)Tm10 cuboctahedra, faces with two equivalent Mg(1)Tm10 cuboctahedra, faces with two equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(2)Tm8Mg4 cuboctahedra, faces with four equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with four equivalent Tm(1)Tm12 cuboctahedra, and faces with six equivalent Tm(5)Tm10Mg2 cuboctahedra. In the second Tm site, Tm(2) is bonded to four equivalent Mg(1), two equivalent Tm(1), two equivalent Tm(2), two equivalent Tm(3), and two equivalent Tm(4) atoms to form TmTm8Mg4 cuboctahedra that share corners with four equivalent Mg(1)Tm10 cuboctahedra, corners with six equivalent Tm(3)Tm10Mg2 cuboctahedra, corners with six equivalent Tm(1)Tm12 cuboctahedra, corners with six equivalent Tm(2)Tm8Mg4 cuboctahedra, edges with three equivalent Tm(3)Tm10Mg2 cuboctahedra, edges with three equivalent Tm(1)Tm12 cuboctahedra, edges with eight equivalent Tm(5)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(5)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(1)Tm12 cuboctahedra, faces with four equivalent Mg(1)Tm10 cuboctahedra, faces with four equivalent Tm(2)Tm8Mg4 cuboctahedra, and faces with six equivalent Tm(4)Tm10Mg2 cuboctahedra. In the third Tm site, Tm(3) is bonded to two equivalent Mg(1), two equivalent Tm(1), two equivalent Tm(2), two equivalent Tm(3), and four equivalent Tm(5) atoms to form TmTm10Mg2 cuboctahedra that share corners with six equivalent Tm(3)Tm10Mg2 cuboctahedra, corners with six equivalent Tm(1)Tm12 cuboctahedra, corners with six equivalent Tm(2)Tm8Mg4 cuboctahedra, edges with three equivalent Tm(1)Tm12 cuboctahedra, edges with three equivalent Tm(2)Tm8Mg4 cuboctahedra, edges with four equivalent Tm(5)Tm10Mg2 cuboctahedra, edges with eight equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(1)Tm12 cuboctahedra, faces with two equivalent Tm(2)Tm8Mg4 cuboctahedra, faces with four equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with four equivalent Tm(5)Tm10Mg2 cuboctahedra, and faces with six equivalent Mg(1)Tm10 cuboctahedra. In the fourth Tm site, Tm(4) is bonded to two equivalent Mg(1), two equivalent Tm(2), two equivalent Tm(4), two equivalent Tm(5), and four equivalent Tm(1) atoms to form TmTm10Mg2 cuboctahedra that share corners with six equivalent Tm(4)Tm10Mg2 cuboctahedra, corners with six equivalent Tm(5)Tm10Mg2 cuboctahedra, corners with eight equivalent Mg(1)Tm10 cuboctahedra,  an edgeedge with one Mg(1)Tm10 cuboctahedra, edges with three equivalent Tm(5)Tm10Mg2 cuboctahedra, edges with four equivalent Tm(1)Tm12 cuboctahedra, edges with eight equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with two equivalent Mg(1)Tm10 cuboctahedra, faces with two equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(5)Tm10Mg2 cuboctahedra, faces with four equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with four equivalent Tm(1)Tm12 cuboctahedra, and faces with six equivalent Tm(2)Tm8Mg4 cuboctahedra. In the fifth Tm site, Tm(5) is bonded to two equivalent Mg(1), two equivalent Tm(1), two equivalent Tm(4), two equivalent Tm(5), and four equivalent Tm(3) atoms to form TmTm10Mg2 cuboctahedra that share corners with six equivalent Tm(4)Tm10Mg2 cuboctahedra, corners with six equivalent Tm(5)Tm10Mg2 cuboctahedra, corners with eight equivalent Mg(1)Tm10 cuboctahedra,  an edgeedge with one Mg(1)Tm10 cuboctahedra, edges with three equivalent Tm(4)Tm10Mg2 cuboctahedra, edges with four equivalent Tm(3)Tm10Mg2 cuboctahedra, edges with eight equivalent Tm(2)Tm8Mg4 cuboctahedra, faces with two equivalent Mg(1)Tm10 cuboctahedra, faces with two equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(2)Tm8Mg4 cuboctahedra, faces with four equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with four equivalent Tm(5)Tm10Mg2 cuboctahedra, and faces with six equivalent Tm(1)Tm12 cuboctahedra.
MgTm5 crystallizes in the orthorhombic Amm2 space group. Mg(1) is bonded to two equivalent Tm(3), two equivalent Tm(4), two equivalent Tm(5), and four equivalent Tm(2) atoms to form distorted MgTm10 cuboctahedra that share corners with four equivalent Mg(1)Tm10 cuboctahedra, corners with four equivalent Tm(2)Tm8Mg4 cuboctahedra, corners with eight equivalent Tm(4)Tm10Mg2 cuboctahedra, corners with eight equivalent Tm(5)Tm10Mg2 cuboctahedra,  an edgeedge with one Tm(4)Tm10Mg2 cuboctahedra,  an edgeedge with one Tm(5)Tm10Mg2 cuboctahedra, edges with eight equivalent Tm(1)Tm12 cuboctahedra, faces with two equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(5)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(1)Tm12 cuboctahedra, faces with four equivalent Mg(1)Tm10 cuboctahedra, faces with four equivalent Tm(2)Tm8Mg4 cuboctahedra, and faces with six equivalent Tm(3)Tm10Mg2 cuboctahedra. Both Mg(1)-Tm(3) bond lengths are 3.39 Å. Both Mg(1)-Tm(4) bond lengths are 3.54 Å. Both Mg(1)-Tm(5) bond lengths are 3.43 Å. All Mg(1)-Tm(2) bond lengths are 3.41 Å. There are five inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to two equivalent Tm(1), two equivalent Tm(2), two equivalent Tm(3), two equivalent Tm(5), and four equivalent Tm(4) atoms to form TmTm12 cuboctahedra that share corners with six equivalent Tm(3)Tm10Mg2 cuboctahedra, corners with six equivalent Tm(1)Tm12 cuboctahedra, corners with six equivalent Tm(2)Tm8Mg4 cuboctahedra, edges with three equivalent Tm(3)Tm10Mg2 cuboctahedra, edges with three equivalent Tm(2)Tm8Mg4 cuboctahedra, edges with four equivalent Tm(4)Tm10Mg2 cuboctahedra, edges with eight equivalent Mg(1)Tm10 cuboctahedra, faces with two equivalent Mg(1)Tm10 cuboctahedra, faces with two equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(2)Tm8Mg4 cuboctahedra, faces with four equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with four equivalent Tm(1)Tm12 cuboctahedra, and faces with six equivalent Tm(5)Tm10Mg2 cuboctahedra. Both Tm(1)-Tm(1) bond lengths are 3.53 Å. Both Tm(1)-Tm(2) bond lengths are 3.55 Å. Both Tm(1)-Tm(3) bond lengths are 3.49 Å. Both Tm(1)-Tm(5) bond lengths are 3.44 Å. All Tm(1)-Tm(4) bond lengths are 3.41 Å. In the second Tm site, Tm(2) is bonded to four equivalent Mg(1), two equivalent Tm(1), two equivalent Tm(2), two equivalent Tm(3), and two equivalent Tm(4) atoms to form TmTm8Mg4 cuboctahedra that share corners with four equivalent Mg(1)Tm10 cuboctahedra, corners with six equivalent Tm(3)Tm10Mg2 cuboctahedra, corners with six equivalent Tm(1)Tm12 cuboctahedra, corners with six equivalent Tm(2)Tm8Mg4 cuboctahedra, edges with three equivalent Tm(3)Tm10Mg2 cuboctahedra, edges with three equivalent Tm(1)Tm12 cuboctahedra, edges with eight equivalent Tm(5)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(5)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(1)Tm12 cuboctahedra, faces with four equivalent Mg(1)Tm10 cuboctahedra, faces with four equivalent Tm(2)Tm8Mg4 cuboctahedra, and faces with six equivalent Tm(4)Tm10Mg2 cuboctahedra. Both Tm(2)-Tm(2) bond lengths are 3.53 Å. Both Tm(2)-Tm(3) bond lengths are 3.42 Å. Both Tm(2)-Tm(4) bond lengths are 3.48 Å. In the third Tm site, Tm(3) is bonded to two equivalent Mg(1), two equivalent Tm(1), two equivalent Tm(2), two equivalent Tm(3), and four equivalent Tm(5) atoms to form TmTm10Mg2 cuboctahedra that share corners with six equivalent Tm(3)Tm10Mg2 cuboctahedra, corners with six equivalent Tm(1)Tm12 cuboctahedra, corners with six equivalent Tm(2)Tm8Mg4 cuboctahedra, edges with three equivalent Tm(1)Tm12 cuboctahedra, edges with three equivalent Tm(2)Tm8Mg4 cuboctahedra, edges with four equivalent Tm(5)Tm10Mg2 cuboctahedra, edges with eight equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(1)Tm12 cuboctahedra, faces with two equivalent Tm(2)Tm8Mg4 cuboctahedra, faces with four equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with four equivalent Tm(5)Tm10Mg2 cuboctahedra, and faces with six equivalent Mg(1)Tm10 cuboctahedra. Both Tm(3)-Tm(3) bond lengths are 3.53 Å. All Tm(3)-Tm(5) bond lengths are 3.41 Å. In the fourth Tm site, Tm(4) is bonded to two equivalent Mg(1), two equivalent Tm(2), two equivalent Tm(4), two equivalent Tm(5), and four equivalent Tm(1) atoms to form TmTm10Mg2 cuboctahedra that share corners with six equivalent Tm(4)Tm10Mg2 cuboctahedra, corners with six equivalent Tm(5)Tm10Mg2 cuboctahedra, corners with eight equivalent Mg(1)Tm10 cuboctahedra,  an edgeedge with one Mg(1)Tm10 cuboctahedra, edges with three equivalent Tm(5)Tm10Mg2 cuboctahedra, edges with four equivalent Tm(1)Tm12 cuboctahedra, edges with eight equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with two equivalent Mg(1)Tm10 cuboctahedra, faces with two equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(5)Tm10Mg2 cuboctahedra, faces with four equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with four equivalent Tm(1)Tm12 cuboctahedra, and faces with six equivalent Tm(2)Tm8Mg4 cuboctahedra. Both Tm(4)-Tm(4) bond lengths are 3.53 Å. Both Tm(4)-Tm(5) bond lengths are 3.49 Å. In the fifth Tm site, Tm(5) is bonded to two equivalent Mg(1), two equivalent Tm(1), two equivalent Tm(4), two equivalent Tm(5), and four equivalent Tm(3) atoms to form TmTm10Mg2 cuboctahedra that share corners with six equivalent Tm(4)Tm10Mg2 cuboctahedra, corners with six equivalent Tm(5)Tm10Mg2 cuboctahedra, corners with eight equivalent Mg(1)Tm10 cuboctahedra,  an edgeedge with one Mg(1)Tm10 cuboctahedra, edges with three equivalent Tm(4)Tm10Mg2 cuboctahedra, edges with four equivalent Tm(3)Tm10Mg2 cuboctahedra, edges with eight equivalent Tm(2)Tm8Mg4 cuboctahedra, faces with two equivalent Mg(1)Tm10 cuboctahedra, faces with two equivalent Tm(4)Tm10Mg2 cuboctahedra, faces with two equivalent Tm(2)Tm8Mg4 cuboctahedra, faces with four equivalent Tm(3)Tm10Mg2 cuboctahedra, faces with four equivalent Tm(5)Tm10Mg2 cuboctahedra, and faces with six equivalent Tm(1)Tm12 cuboctahedra. Both Tm(5)-Tm(5) bond lengths are 3.53 Å.