MgAg2(O2Br)2 crystallizes in the monoclinic Pm space group. Mg(1) is bonded in a 7-coordinate geometry to one O(2), one O(4), two equivalent O(1), two equivalent O(3), and one Br(2) atom. There are two inequivalent Ag sites. In the first Ag site, Ag(1) is bonded to one O(3), one Br(1), and four equivalent Br(2) atoms to form a mixture of distorted edge and corner-sharing AgBr5O octahedra. The corner-sharing octahedral tilt angles are 11°. In the second Ag site, Ag(2) is bonded to one O(2), one Br(2), and four equivalent Br(1) atoms to form a mixture of edge and corner-sharing AgBr5O octahedra. The corner-sharing octahedral tilt angles are 3°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Mg(1) and one O(3) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Ag(2), and one O(4) atom. In the third O site, O(3) is bonded to two equivalent Mg(1), one Ag(1), and one O(1) atom to form distorted OMg2AgO tetrahedra that share corners with two equivalent Br(2)MgAg5 octahedra,  a cornercorner with one Br(1)Ag5 square pyramid, corners with two equivalent O(3)Mg2AgO tetrahedra, and edges with two equivalent Br(2)MgAg5 octahedra. The corner-sharing octahedral tilt angles are 92°. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Mg(1) and one O(2) atom. There are two inequivalent Br sites. In the first Br site, Br(1) is bonded to one Ag(1) and four equivalent Ag(2) atoms to form BrAg5 square pyramids that share corners with four equivalent Br(1)Ag5 square pyramids,  a cornercorner with one O(3)Mg2AgO tetrahedra, edges with four equivalent Br(2)MgAg5 octahedra, and edges with four equivalent Br(1)Ag5 square pyramids. In the second Br site, Br(2) is bonded to one Mg(1), one Ag(2), and four equivalent Ag(1) atoms to form BrMgAg5 octahedra that share corners with four equivalent Br(2)MgAg5 octahedra, corners with two equivalent O(3)Mg2AgO tetrahedra, edges with four equivalent Br(2)MgAg5 octahedra, edges with four equivalent Br(1)Ag5 square pyramids, and edges with two equivalent O(3)Mg2AgO tetrahedra. The corner-sharing octahedral tilt angles are 11°.
MgAg2(O2Br)2 crystallizes in the monoclinic Pm space group. Mg(1) is bonded in a 7-coordinate geometry to one O(2), one O(4), two equivalent O(1), two equivalent O(3), and one Br(2) atom. The Mg(1)-O(2) bond length is 2.20 Å. The Mg(1)-O(4) bond length is 2.23 Å. Both Mg(1)-O(1) bond lengths are 2.01 Å. Both Mg(1)-O(3) bond lengths are 2.08 Å. The Mg(1)-Br(2) bond length is 3.02 Å. There are two inequivalent Ag sites. In the first Ag site, Ag(1) is bonded to one O(3), one Br(1), and four equivalent Br(2) atoms to form a mixture of distorted edge and corner-sharing AgBr5O octahedra. The corner-sharing octahedral tilt angles are 11°. The Ag(1)-O(3) bond length is 2.44 Å. The Ag(1)-Br(1) bond length is 2.76 Å. All Ag(1)-Br(2) bond lengths are 2.90 Å. In the second Ag site, Ag(2) is bonded to one O(2), one Br(2), and four equivalent Br(1) atoms to form a mixture of edge and corner-sharing AgBr5O octahedra. The corner-sharing octahedral tilt angles are 3°. The Ag(2)-O(2) bond length is 2.57 Å. The Ag(2)-Br(2) bond length is 2.97 Å. There are two shorter (2.88 Å) and two longer (2.89 Å) Ag(2)-Br(1) bond lengths. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Mg(1) and one O(3) atom. The O(1)-O(3) bond length is 1.49 Å. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Ag(2), and one O(4) atom. The O(2)-O(4) bond length is 1.30 Å. In the third O site, O(3) is bonded to two equivalent Mg(1), one Ag(1), and one O(1) atom to form distorted OMg2AgO tetrahedra that share corners with two equivalent Br(2)MgAg5 octahedra,  a cornercorner with one Br(1)Ag5 square pyramid, corners with two equivalent O(3)Mg2AgO tetrahedra, and edges with two equivalent Br(2)MgAg5 octahedra. The corner-sharing octahedral tilt angles are 92°. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Mg(1) and one O(2) atom. There are two inequivalent Br sites. In the first Br site, Br(1) is bonded to one Ag(1) and four equivalent Ag(2) atoms to form BrAg5 square pyramids that share corners with four equivalent Br(1)Ag5 square pyramids,  a cornercorner with one O(3)Mg2AgO tetrahedra, edges with four equivalent Br(2)MgAg5 octahedra, and edges with four equivalent Br(1)Ag5 square pyramids. In the second Br site, Br(2) is bonded to one Mg(1), one Ag(2), and four equivalent Ag(1) atoms to form BrMgAg5 octahedra that share corners with four equivalent Br(2)MgAg5 octahedra, corners with two equivalent O(3)Mg2AgO tetrahedra, edges with four equivalent Br(2)MgAg5 octahedra, edges with four equivalent Br(1)Ag5 square pyramids, and edges with two equivalent O(3)Mg2AgO tetrahedra. The corner-sharing octahedral tilt angles are 11°.