MgTm6WO12 crystallizes in the trigonal R3 space group. Mg(1) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form MgO6 octahedra that share  a faceface with one W(1)O6 octahedra. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. In the second Tm site, Tm(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. W(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form WO6 octahedra that share  a faceface with one Mg(1)O6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Tm(2), two equivalent Tm(1), and one W(1) atom to form distorted OTm3W trigonal pyramids that share corners with six equivalent O(4)Tm4 tetrahedra and corners with four equivalent O(1)Tm3W trigonal pyramids. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Tm(2), and one W(1) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Tm(1), and two equivalent Tm(2) atoms. In the fourth O site, O(4) is bonded to two equivalent Tm(1) and two equivalent Tm(2) atoms to form OTm4 tetrahedra that share corners with four equivalent O(4)Tm4 tetrahedra and corners with six equivalent O(1)Tm3W trigonal pyramids.
MgTm6WO12 crystallizes in the trigonal R3 space group. Mg(1) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form MgO6 octahedra that share  a faceface with one W(1)O6 octahedra. All Mg(1)-O(2) bond lengths are 2.11 Å. All Mg(1)-O(3) bond lengths are 2.13 Å. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. There is one shorter (2.28 Å) and one longer (2.30 Å) Tm(1)-O(1) bond length. There is one shorter (2.35 Å) and one longer (2.36 Å) Tm(1)-O(3) bond length. There is one shorter (2.22 Å) and one longer (2.23 Å) Tm(1)-O(4) bond length. In the second Tm site, Tm(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. The Tm(2)-O(1) bond length is 2.51 Å. There is one shorter (2.17 Å) and one longer (2.36 Å) Tm(2)-O(2) bond length. There is one shorter (2.22 Å) and one longer (2.45 Å) Tm(2)-O(3) bond length. There is one shorter (2.19 Å) and one longer (2.31 Å) Tm(2)-O(4) bond length. W(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form WO6 octahedra that share  a faceface with one Mg(1)O6 octahedra. All W(1)-O(1) bond lengths are 2.08 Å. All W(1)-O(2) bond lengths are 2.12 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Tm(2), two equivalent Tm(1), and one W(1) atom to form distorted OTm3W trigonal pyramids that share corners with six equivalent O(4)Tm4 tetrahedra and corners with four equivalent O(1)Tm3W trigonal pyramids. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Tm(2), and one W(1) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Tm(1), and two equivalent Tm(2) atoms. In the fourth O site, O(4) is bonded to two equivalent Tm(1) and two equivalent Tm(2) atoms to form OTm4 tetrahedra that share corners with four equivalent O(4)Tm4 tetrahedra and corners with six equivalent O(1)Tm3W trigonal pyramids.