Sr6Mg(W2O9)2 crystallizes in the trigonal R-3 space group. Sr(1) is bonded to four equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms to form distorted SrO12 cuboctahedra that share corners with six equivalent Sr(1)O12 cuboctahedra,  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent W(1)O6 octahedra, corners with two equivalent W(2)O6 octahedra, faces with eight equivalent Sr(1)O12 cuboctahedra,  a faceface with one Mg(1)O6 octahedra, faces with two equivalent W(1)O6 octahedra, and faces with two equivalent W(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-31°. Mg(1) is bonded to six equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, faces with six equivalent Sr(1)O12 cuboctahedra, and faces with two equivalent W(1)O6 octahedra. There are two inequivalent W sites. In the first W site, W(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form WO6 octahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, faces with six equivalent Sr(1)O12 cuboctahedra,  a faceface with one Mg(1)O6 octahedra, and  a faceface with one W(2)O6 octahedra. In the second W site, W(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form distorted WO6 octahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, faces with six equivalent Sr(1)O12 cuboctahedra, and  a faceface with one W(1)O6 octahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to four equivalent Sr(1), one Mg(1), and one W(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to four equivalent Sr(1), one W(1), and one W(2) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to four equivalent Sr(1) and one W(2) atom.
Sr6Mg(W2O9)2 crystallizes in the trigonal R-3 space group. Sr(1) is bonded to four equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms to form distorted SrO12 cuboctahedra that share corners with six equivalent Sr(1)O12 cuboctahedra,  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent W(1)O6 octahedra, corners with two equivalent W(2)O6 octahedra, faces with eight equivalent Sr(1)O12 cuboctahedra,  a faceface with one Mg(1)O6 octahedra, faces with two equivalent W(1)O6 octahedra, and faces with two equivalent W(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-31°. There are a spread of Sr(1)-O(1) bond distances ranging from 2.77-3.15 Å. There are a spread of Sr(1)-O(2) bond distances ranging from 2.81-3.19 Å. There are a spread of Sr(1)-O(3) bond distances ranging from 2.83-2.97 Å. Mg(1) is bonded to six equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, faces with six equivalent Sr(1)O12 cuboctahedra, and faces with two equivalent W(1)O6 octahedra. All Mg(1)-O(1) bond lengths are 2.13 Å. There are two inequivalent W sites. In the first W site, W(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form WO6 octahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, faces with six equivalent Sr(1)O12 cuboctahedra,  a faceface with one Mg(1)O6 octahedra, and  a faceface with one W(2)O6 octahedra. All W(1)-O(1) bond lengths are 1.97 Å. All W(1)-O(2) bond lengths are 2.05 Å. In the second W site, W(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form distorted WO6 octahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, faces with six equivalent Sr(1)O12 cuboctahedra, and  a faceface with one W(1)O6 octahedra. All W(2)-O(2) bond lengths are 2.14 Å. All W(2)-O(3) bond lengths are 1.84 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to four equivalent Sr(1), one Mg(1), and one W(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to four equivalent Sr(1), one W(1), and one W(2) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to four equivalent Sr(1) and one W(2) atom.