Sr4MgMn2(GaO5)2 crystallizes in the monoclinic C2 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(7), and two equivalent O(5) atoms. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(7), and three equivalent O(6) atoms. Mg(1) is bonded in a 4-coordinate geometry to two equivalent O(5) and two equivalent O(7) atoms. Mn(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(6) atom to form MnO5 square pyramids that share corners with four equivalent Mn(1)O5 square pyramids and  a cornercorner with one Ga(1)O4 trigonal pyramid. Ga(1) is bonded to one O(5), one O(6), and two equivalent O(7) atoms to form distorted GaO4 trigonal pyramids that share  a cornercorner with one Mn(1)O5 square pyramid and  an edgeedge with one Ga(1)O4 trigonal pyramid. There are seven inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Mn(1) atoms to form distorted OSr4Mn2 octahedra that share corners with two equivalent O(4)Sr4Mn2 octahedra, corners with four equivalent O(7)Sr2MgGa2 trigonal bipyramids, edges with two equivalent O(4)Sr4Mn2 octahedra, faces with two equivalent O(2)Sr4Mn2 octahedra, and faces with two equivalent O(3)Sr4Mn2 octahedra. The corner-sharing octahedral tilt angles are 9°. In the second O site, O(2) is bonded to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Mn(1) atoms to form distorted OSr4Mn2 octahedra that share corners with two equivalent O(3)Sr4Mn2 octahedra, corners with four equivalent O(7)Sr2MgGa2 trigonal bipyramids, edges with two equivalent O(3)Sr4Mn2 octahedra, faces with two equivalent O(1)Sr4Mn2 octahedra, and faces with two equivalent O(4)Sr4Mn2 octahedra. The corner-sharing octahedral tilt angles are 12°. In the third O site, O(3) is bonded to two equivalent Sr(1), two equivalent Sr(2), 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(7)Sr2MgGa2 trigonal bipyramids, edges with two equivalent O(2)Sr4Mn2 octahedra, faces with two equivalent O(1)Sr4Mn2 octahedra, and faces with two equivalent O(4)Sr4Mn2 octahedra. The corner-sharing octahedral tilt angles are 12°. In the fourth O site, O(4) is bonded to two equivalent Sr(1), two equivalent Sr(2), 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(7)Sr2MgGa2 trigonal bipyramids, edges with two equivalent O(1)Sr4Mn2 octahedra, faces with two equivalent O(2)Sr4Mn2 octahedra, and faces with two equivalent O(3)Sr4Mn2 octahedra. The corner-sharing octahedral tilt angles are 9°. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to two equivalent Sr(1), one Mg(1), and one Ga(1) atom. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to three equivalent Sr(2), one Mn(1), and one Ga(1) atom. In the seventh O site, O(7) is bonded to one Sr(1), one Sr(2), one Mg(1), and two equivalent Ga(1) atoms to form distorted OSr2MgGa2 trigonal bipyramids that share corners with two equivalent O(1)Sr4Mn2 octahedra, corners with two equivalent O(2)Sr4Mn2 octahedra, corners with two equivalent O(3)Sr4Mn2 octahedra, corners with two equivalent O(4)Sr4Mn2 octahedra,  a cornercorner with one O(7)Sr2MgGa2 trigonal bipyramid, and  an edgeedge with one O(7)Sr2MgGa2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 31-71°.
Sr4MgMn2(GaO5)2 crystallizes in the monoclinic C2 space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(7), and two equivalent O(5) atoms. The Sr(1)-O(1) bond length is 2.66 Å. The Sr(1)-O(2) bond length is 2.55 Å. The Sr(1)-O(3) bond length is 2.60 Å. The Sr(1)-O(4) bond length is 2.54 Å. The Sr(1)-O(7) bond length is 2.79 Å. There is one shorter (2.78 Å) and one longer (3.01 Å) Sr(1)-O(5) bond length. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(7), and three equivalent O(6) atoms. The Sr(2)-O(1) bond length is 2.63 Å. The Sr(2)-O(2) bond length is 2.72 Å. The Sr(2)-O(3) bond length is 2.71 Å. The Sr(2)-O(4) bond length is 2.70 Å. The Sr(2)-O(7) bond length is 2.57 Å. There are a spread of Sr(2)-O(6) bond distances ranging from 2.64-3.00 Å. Mg(1) is bonded in a 4-coordinate geometry to two equivalent O(5) and two equivalent O(7) atoms. Both Mg(1)-O(5) bond lengths are 2.03 Å. Both Mg(1)-O(7) bond lengths are 2.01 Å. Mn(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(6) atom to form MnO5 square pyramids that share corners with four equivalent Mn(1)O5 square pyramids and  a cornercorner with one Ga(1)O4 trigonal pyramid. The Mn(1)-O(1) bond length is 2.06 Å. The Mn(1)-O(2) bond length is 2.06 Å. The Mn(1)-O(3) bond length is 2.03 Å. The Mn(1)-O(4) bond length is 2.05 Å. The Mn(1)-O(6) bond length is 2.29 Å. Ga(1) is bonded to one O(5), one O(6), and two equivalent O(7) atoms to form distorted GaO4 trigonal pyramids that share  a cornercorner with one Mn(1)O5 square pyramid and  an edgeedge with one Ga(1)O4 trigonal pyramid. The Ga(1)-O(5) bond length is 1.87 Å. The Ga(1)-O(6) bond length is 1.85 Å. There is one shorter (1.91 Å) and one longer (2.19 Å) Ga(1)-O(7) bond length. There are seven inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Mn(1) atoms to form distorted OSr4Mn2 octahedra that share corners with two equivalent O(4)Sr4Mn2 octahedra, corners with four equivalent O(7)Sr2MgGa2 trigonal bipyramids, edges with two equivalent O(4)Sr4Mn2 octahedra, faces with two equivalent O(2)Sr4Mn2 octahedra, and faces with two equivalent O(3)Sr4Mn2 octahedra. The corner-sharing octahedral tilt angles are 9°. In the second O site, O(2) is bonded to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Mn(1) atoms to form distorted OSr4Mn2 octahedra that share corners with two equivalent O(3)Sr4Mn2 octahedra, corners with four equivalent O(7)Sr2MgGa2 trigonal bipyramids, edges with two equivalent O(3)Sr4Mn2 octahedra, faces with two equivalent O(1)Sr4Mn2 octahedra, and faces with two equivalent O(4)Sr4Mn2 octahedra. The corner-sharing octahedral tilt angles are 12°. In the third O site, O(3) is bonded to two equivalent Sr(1), two equivalent Sr(2), 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(7)Sr2MgGa2 trigonal bipyramids, edges with two equivalent O(2)Sr4Mn2 octahedra, faces with two equivalent O(1)Sr4Mn2 octahedra, and faces with two equivalent O(4)Sr4Mn2 octahedra. The corner-sharing octahedral tilt angles are 12°. In the fourth O site, O(4) is bonded to two equivalent Sr(1), two equivalent Sr(2), 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(7)Sr2MgGa2 trigonal bipyramids, edges with two equivalent O(1)Sr4Mn2 octahedra, faces with two equivalent O(2)Sr4Mn2 octahedra, and faces with two equivalent O(3)Sr4Mn2 octahedra. The corner-sharing octahedral tilt angles are 9°. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to two equivalent Sr(1), one Mg(1), and one Ga(1) atom. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to three equivalent Sr(2), one Mn(1), and one Ga(1) atom. In the seventh O site, O(7) is bonded to one Sr(1), one Sr(2), one Mg(1), and two equivalent Ga(1) atoms to form distorted OSr2MgGa2 trigonal bipyramids that share corners with two equivalent O(1)Sr4Mn2 octahedra, corners with two equivalent O(2)Sr4Mn2 octahedra, corners with two equivalent O(3)Sr4Mn2 octahedra, corners with two equivalent O(4)Sr4Mn2 octahedra,  a cornercorner with one O(7)Sr2MgGa2 trigonal bipyramid, and  an edgeedge with one O(7)Sr2MgGa2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 31-71°.