Sr2MnGaO5 crystallizes in the monoclinic C2/m space group. Sr(1) is bonded in a 9-coordinate geometry to one O(3), two equivalent O(1), two equivalent O(2), and four equivalent O(4) atoms. Mn(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form MnO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra and corners with two equivalent Ga(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 2-6°. Ga(1) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form distorted GaO4 tetrahedra that share corners with two equivalent Mn(1)O6 octahedra and  an edgeedge with one Ga(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 27°. There are four inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Sr(1) and two equivalent Mn(1) atoms to form distorted OSr4Mn2 octahedra that share corners with two equivalent O(1)Sr4Mn2 octahedra, corners with four equivalent O(3)Sr2Ga2 trigonal pyramids, edges with two equivalent O(1)Sr4Mn2 octahedra, and faces with four equivalent O(2)Sr4Mn2 octahedra. The corner-sharing octahedra are not tilted. In the second O site, O(2) is bonded to four equivalent Sr(1) and two equivalent Mn(1) atoms to form distorted OSr4Mn2 octahedra that share corners with two equivalent O(2)Sr4Mn2 octahedra, corners with four equivalent O(3)Sr2Ga2 trigonal pyramids, edges with two equivalent O(2)Sr4Mn2 octahedra, and faces with four equivalent O(1)Sr4Mn2 octahedra. The corner-sharing octahedra are not tilted. In the third O site, O(3) is bonded to two equivalent Sr(1) and two equivalent Ga(1) atoms to form OSr2Ga2 trigonal pyramids that share corners with four equivalent O(1)Sr4Mn2 octahedra, corners with four equivalent O(2)Sr4Mn2 octahedra, and  an edgeedge with one O(3)Sr2Ga2 trigonal pyramid. The corner-sharing octahedral tilt angles range from 26-68°. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to four equivalent Sr(1), one Mn(1), and one Ga(1) atom.
Sr2MnGaO5 crystallizes in the monoclinic C2/m space group. Sr(1) is bonded in a 9-coordinate geometry to one O(3), two equivalent O(1), two equivalent O(2), and four equivalent O(4) atoms. The Sr(1)-O(3) bond length is 2.40 Å. There is one shorter (2.68 Å) and one longer (2.71 Å) Sr(1)-O(1) bond length. There is one shorter (2.66 Å) and one longer (2.69 Å) Sr(1)-O(2) bond length. There are a spread of Sr(1)-O(4) bond distances ranging from 2.58-3.07 Å. Mn(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form MnO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra and corners with two equivalent Ga(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 2-6°. Both Mn(1)-O(1) bond lengths are 1.94 Å. Both Mn(1)-O(2) bond lengths are 1.96 Å. Both Mn(1)-O(4) bond lengths are 2.43 Å. Ga(1) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form distorted GaO4 tetrahedra that share corners with two equivalent Mn(1)O6 octahedra and  an edgeedge with one Ga(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 27°. There is one shorter (1.94 Å) and one longer (1.95 Å) Ga(1)-O(3) bond length. Both Ga(1)-O(4) bond lengths are 1.86 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Sr(1) and two equivalent Mn(1) atoms to form distorted OSr4Mn2 octahedra that share corners with two equivalent O(1)Sr4Mn2 octahedra, corners with four equivalent O(3)Sr2Ga2 trigonal pyramids, edges with two equivalent O(1)Sr4Mn2 octahedra, and faces with four equivalent O(2)Sr4Mn2 octahedra. The corner-sharing octahedra are not tilted. In the second O site, O(2) is bonded to four equivalent Sr(1) and two equivalent Mn(1) atoms to form distorted OSr4Mn2 octahedra that share corners with two equivalent O(2)Sr4Mn2 octahedra, corners with four equivalent O(3)Sr2Ga2 trigonal pyramids, edges with two equivalent O(2)Sr4Mn2 octahedra, and faces with four equivalent O(1)Sr4Mn2 octahedra. The corner-sharing octahedra are not tilted. In the third O site, O(3) is bonded to two equivalent Sr(1) and two equivalent Ga(1) atoms to form OSr2Ga2 trigonal pyramids that share corners with four equivalent O(1)Sr4Mn2 octahedra, corners with four equivalent O(2)Sr4Mn2 octahedra, and  an edgeedge with one O(3)Sr2Ga2 trigonal pyramid. The corner-sharing octahedral tilt angles range from 26-68°. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to four equivalent Sr(1), one Mn(1), and one Ga(1) atom.