Sr3Mn4O12 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form SrO12 cuboctahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, corners with six equivalent Mn(1)O6 octahedra, faces with six equivalent Sr(2)O12 cuboctahedra, and faces with six equivalent Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles are 11°. In the second Sr site, Sr(2) is bonded to three equivalent O(1), three equivalent O(3), and six equivalent O(2) atoms to form SrO12 cuboctahedra that share corners with twelve equivalent Sr(2)O12 cuboctahedra, faces with three equivalent Sr(1)O12 cuboctahedra, faces with four equivalent Mn(1)O6 octahedra, and faces with four equivalent Mn(2)O6 octahedra. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form MnO6 octahedra that share corners with three equivalent Sr(1)O12 cuboctahedra, corners with three equivalent Mn(1)O6 octahedra, faces with four equivalent Sr(2)O12 cuboctahedra, and  a faceface with one Mn(2)O6 octahedra. The corner-sharing octahedra are not tilted. In the second Mn site, Mn(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MnO6 octahedra that share corners with three equivalent Mn(2)O6 octahedra, faces with three equivalent Sr(1)O12 cuboctahedra, faces with four equivalent Sr(2)O12 cuboctahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedra are not tilted. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Mn(2) atoms. In the second O site, O(2) is bonded in a distorted L-shaped geometry to one Sr(1), two equivalent Sr(2), one Mn(1), and one Mn(2) atom. In the third O site, O(3) is bonded in a distorted linear geometry to two equivalent Sr(2) and two equivalent Mn(1) atoms.
Sr3Mn4O12 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form SrO12 cuboctahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, corners with six equivalent Mn(1)O6 octahedra, faces with six equivalent Sr(2)O12 cuboctahedra, and faces with six equivalent Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles are 11°. All Sr(1)-O(1) bond lengths are 2.76 Å. All Sr(1)-O(2) bond lengths are 2.90 Å. In the second Sr site, Sr(2) is bonded to three equivalent O(1), three equivalent O(3), and six equivalent O(2) atoms to form SrO12 cuboctahedra that share corners with twelve equivalent Sr(2)O12 cuboctahedra, faces with three equivalent Sr(1)O12 cuboctahedra, faces with four equivalent Mn(1)O6 octahedra, and faces with four equivalent Mn(2)O6 octahedra. All Sr(2)-O(1) bond lengths are 2.88 Å. All Sr(2)-O(3) bond lengths are 2.77 Å. All Sr(2)-O(2) bond lengths are 2.76 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form MnO6 octahedra that share corners with three equivalent Sr(1)O12 cuboctahedra, corners with three equivalent Mn(1)O6 octahedra, faces with four equivalent Sr(2)O12 cuboctahedra, and  a faceface with one Mn(2)O6 octahedra. The corner-sharing octahedra are not tilted. All Mn(1)-O(2) bond lengths are 1.93 Å. All Mn(1)-O(3) bond lengths are 1.91 Å. In the second Mn site, Mn(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MnO6 octahedra that share corners with three equivalent Mn(2)O6 octahedra, faces with three equivalent Sr(1)O12 cuboctahedra, faces with four equivalent Sr(2)O12 cuboctahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedra are not tilted. All Mn(2)-O(1) bond lengths are 1.90 Å. All Mn(2)-O(2) bond lengths are 1.91 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Mn(2) atoms. In the second O site, O(2) is bonded in a distorted L-shaped geometry to one Sr(1), two equivalent Sr(2), one Mn(1), and one Mn(2) atom. In the third O site, O(3) is bonded in a distorted linear geometry to two equivalent Sr(2) and two equivalent Mn(1) atoms.