Sr3Co2O9 crystallizes in the monoclinic C2/m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 9-coordinate geometry to one O(3), two equivalent O(1), two equivalent O(4), and four equivalent O(2) atoms. In the second Sr site, Sr(2) is bonded to four equivalent O(1), four equivalent O(4), and four equivalent O(5) atoms to form a mixture of corner and face-sharing SrO12 cuboctahedra. Co(1) is bonded in a 5-coordinate geometry to one O(2), one O(5), two equivalent O(1), and two equivalent O(4) atoms. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Co(1) atoms. In the second O site, O(2) is bonded to four equivalent Sr(1), one Co(1), and one O(3) atom to form distorted OSr4CoO octahedra that share  a cornercorner with one O(5)Sr4Co2 octahedra, corners with four equivalent O(2)Sr4CoO octahedra, and edges with four equivalent O(2)Sr4CoO octahedra. The corner-sharing octahedral tilt angles range from 1-24°. In the third O site, O(3) is bonded in a linear geometry to one Sr(1) and one O(2) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Co(1) atoms. In the fifth O site, O(5) is bonded to four equivalent Sr(2) and two equivalent Co(1) atoms to form distorted OSr4Co2 octahedra that share corners with two equivalent O(2)Sr4CoO octahedra, corners with four equivalent O(5)Sr4Co2 octahedra, and edges with four equivalent O(5)Sr4Co2 octahedra. The corner-sharing octahedral tilt angles range from 0-1°.
Sr3Co2O9 crystallizes in the monoclinic C2/m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 9-coordinate geometry to one O(3), two equivalent O(1), two equivalent O(4), and four equivalent O(2) atoms. The Sr(1)-O(3) bond length is 2.61 Å. There is one shorter (2.55 Å) and one longer (2.56 Å) Sr(1)-O(1) bond length. Both Sr(1)-O(4) bond lengths are 2.62 Å. There are two shorter (2.77 Å) and two longer (2.80 Å) Sr(1)-O(2) bond lengths. In the second Sr site, Sr(2) is bonded to four equivalent O(1), four equivalent O(4), and four equivalent O(5) atoms to form a mixture of corner and face-sharing SrO12 cuboctahedra. There are two shorter (2.89 Å) and two longer (2.91 Å) Sr(2)-O(1) bond lengths. All Sr(2)-O(4) bond lengths are 2.93 Å. All Sr(2)-O(5) bond lengths are 2.72 Å. Co(1) is bonded in a 5-coordinate geometry to one O(2), one O(5), two equivalent O(1), and two equivalent O(4) atoms. The Co(1)-O(2) bond length is 2.59 Å. The Co(1)-O(5) bond length is 1.91 Å. Both Co(1)-O(1) bond lengths are 1.98 Å. There is one shorter (1.90 Å) and one longer (1.92 Å) Co(1)-O(4) bond length. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Co(1) atoms. In the second O site, O(2) is bonded to four equivalent Sr(1), one Co(1), and one O(3) atom to form distorted OSr4CoO octahedra that share  a cornercorner with one O(5)Sr4Co2 octahedra, corners with four equivalent O(2)Sr4CoO octahedra, and edges with four equivalent O(2)Sr4CoO octahedra. The corner-sharing octahedral tilt angles range from 1-24°. The O(2)-O(3) bond length is 1.36 Å. In the third O site, O(3) is bonded in a linear geometry to one Sr(1) and one O(2) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Co(1) atoms. In the fifth O site, O(5) is bonded to four equivalent Sr(2) and two equivalent Co(1) atoms to form distorted OSr4Co2 octahedra that share corners with two equivalent O(2)Sr4CoO octahedra, corners with four equivalent O(5)Sr4Co2 octahedra, and edges with four equivalent O(5)Sr4Co2 octahedra. The corner-sharing octahedral tilt angles range from 0-1°.