Sr3W2O9 crystallizes in the monoclinic P2_1/m space group. There are three inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one O(1), one O(3), one O(4), and two equivalent O(2) atoms to form distorted SrO5 trigonal bipyramids that share  a cornercorner with one W(2)O4 tetrahedra, corners with three equivalent W(1)O4 tetrahedra,  a cornercorner with one Sr(3)O5 trigonal bipyramid, and edges with two equivalent Sr(2)O6 octahedra. In the second Sr site, Sr(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form SrO6 octahedra that share corners with two equivalent Sr(2)O6 octahedra, corners with two equivalent W(1)O4 tetrahedra, corners with two equivalent W(2)O4 tetrahedra, edges with two equivalent Sr(1)O5 trigonal bipyramids, and edges with two equivalent Sr(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 62°. In the third Sr site, Sr(3) is bonded to one O(1), one O(5), one O(7), and two equivalent O(6) atoms to form distorted SrO5 trigonal bipyramids that share  a cornercorner with one W(1)O4 tetrahedra, corners with three equivalent W(2)O4 tetrahedra,  a cornercorner with one Sr(1)O5 trigonal bipyramid, and edges with two equivalent Sr(2)O6 octahedra. There are two inequivalent W sites. In the first W site, W(1) is bonded to one O(3), one O(5), and two equivalent O(2) atoms to form WO4 tetrahedra that share corners with two equivalent Sr(2)O6 octahedra,  a cornercorner with one Sr(3)O5 trigonal bipyramid, and corners with three equivalent Sr(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 48°. In the second W site, W(2) is bonded to one O(4), one O(7), and two equivalent O(6) atoms to form WO4 tetrahedra that share corners with two equivalent Sr(2)O6 octahedra,  a cornercorner with one Sr(1)O5 trigonal bipyramid, and corners with three equivalent Sr(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 43°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Sr(1), one Sr(3), and two equivalent Sr(2) atoms to form corner-sharing OSr4 tetrahedra. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Sr(1), one Sr(2), and one W(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Sr(1) and one W(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to one Sr(1) and one W(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Sr(3) and one W(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Sr(2), one Sr(3), and one W(2) atom. In the seventh O site, O(7) is bonded in a linear geometry to one Sr(3) and one W(2) atom.
Sr3W2O9 crystallizes in the monoclinic P2_1/m space group. There are three inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one O(1), one O(3), one O(4), and two equivalent O(2) atoms to form distorted SrO5 trigonal bipyramids that share  a cornercorner with one W(2)O4 tetrahedra, corners with three equivalent W(1)O4 tetrahedra,  a cornercorner with one Sr(3)O5 trigonal bipyramid, and edges with two equivalent Sr(2)O6 octahedra. The Sr(1)-O(1) bond length is 2.35 Å. The Sr(1)-O(3) bond length is 2.47 Å. The Sr(1)-O(4) bond length is 2.41 Å. Both Sr(1)-O(2) bond lengths are 2.62 Å. In the second Sr site, Sr(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form SrO6 octahedra that share corners with two equivalent Sr(2)O6 octahedra, corners with two equivalent W(1)O4 tetrahedra, corners with two equivalent W(2)O4 tetrahedra, edges with two equivalent Sr(1)O5 trigonal bipyramids, and edges with two equivalent Sr(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 62°. Both Sr(2)-O(1) bond lengths are 2.37 Å. Both Sr(2)-O(2) bond lengths are 2.65 Å. Both Sr(2)-O(6) bond lengths are 2.63 Å. In the third Sr site, Sr(3) is bonded to one O(1), one O(5), one O(7), and two equivalent O(6) atoms to form distorted SrO5 trigonal bipyramids that share  a cornercorner with one W(1)O4 tetrahedra, corners with three equivalent W(2)O4 tetrahedra,  a cornercorner with one Sr(1)O5 trigonal bipyramid, and edges with two equivalent Sr(2)O6 octahedra. The Sr(3)-O(1) bond length is 2.35 Å. The Sr(3)-O(5) bond length is 2.42 Å. The Sr(3)-O(7) bond length is 2.46 Å. Both Sr(3)-O(6) bond lengths are 2.63 Å. There are two inequivalent W sites. In the first W site, W(1) is bonded to one O(3), one O(5), and two equivalent O(2) atoms to form WO4 tetrahedra that share corners with two equivalent Sr(2)O6 octahedra,  a cornercorner with one Sr(3)O5 trigonal bipyramid, and corners with three equivalent Sr(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 48°. The W(1)-O(3) bond length is 1.81 Å. The W(1)-O(5) bond length is 1.80 Å. Both W(1)-O(2) bond lengths are 1.83 Å. In the second W site, W(2) is bonded to one O(4), one O(7), and two equivalent O(6) atoms to form WO4 tetrahedra that share corners with two equivalent Sr(2)O6 octahedra,  a cornercorner with one Sr(1)O5 trigonal bipyramid, and corners with three equivalent Sr(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 43°. The W(2)-O(4) bond length is 1.80 Å. The W(2)-O(7) bond length is 1.80 Å. Both W(2)-O(6) bond lengths are 1.83 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Sr(1), one Sr(3), and two equivalent Sr(2) atoms to form corner-sharing OSr4 tetrahedra. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Sr(1), one Sr(2), and one W(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Sr(1) and one W(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to one Sr(1) and one W(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Sr(3) and one W(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Sr(2), one Sr(3), and one W(2) atom. In the seventh O site, O(7) is bonded in a linear geometry to one Sr(3) and one W(2) atom.