MgFeAs2O7 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted MgO6 pentagonal pyramids that share corners with six equivalent As(1)O4 tetrahedra and edges with three equivalent Fe(1)O6 pentagonal pyramids. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted FeO6 pentagonal pyramids that share corners with six equivalent As(1)O4 tetrahedra and edges with three equivalent Mg(1)O6 pentagonal pyramids. As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share corners with three equivalent Mg(1)O6 pentagonal pyramids, corners with three equivalent Fe(1)O6 pentagonal pyramids, and  a cornercorner with one As(1)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one As(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one As(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one As(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to two equivalent As(1) atoms.
MgFeAs2O7 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted MgO6 pentagonal pyramids that share corners with six equivalent As(1)O4 tetrahedra and edges with three equivalent Fe(1)O6 pentagonal pyramids. Both Mg(1)-O(1) bond lengths are 2.12 Å. Both Mg(1)-O(2) bond lengths are 2.12 Å. Both Mg(1)-O(3) bond lengths are 2.24 Å. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted FeO6 pentagonal pyramids that share corners with six equivalent As(1)O4 tetrahedra and edges with three equivalent Mg(1)O6 pentagonal pyramids. Both Fe(1)-O(1) bond lengths are 2.17 Å. Both Fe(1)-O(2) bond lengths are 2.18 Å. Both Fe(1)-O(3) bond lengths are 2.13 Å. As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share corners with three equivalent Mg(1)O6 pentagonal pyramids, corners with three equivalent Fe(1)O6 pentagonal pyramids, and  a cornercorner with one As(1)O4 tetrahedra. The As(1)-O(1) bond length is 1.72 Å. The As(1)-O(2) bond length is 1.72 Å. The As(1)-O(3) bond length is 1.70 Å. The As(1)-O(4) bond length is 1.75 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one As(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one As(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one As(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to two equivalent As(1) atoms.