MgFeAs2O7 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(6) atom to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one As(1)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra,  an edgeedge with one As(1)O4 tetrahedra, and edges with two equivalent Fe(1)O5 trigonal bipyramids. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(5) atom to form distorted FeO5 trigonal bipyramids that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form AsO4 tetrahedra that share  a cornercorner with one As(2)O4 tetrahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, corners with three equivalent Fe(1)O5 trigonal bipyramids, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. In the second As site, As(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form AsO4 tetrahedra that share  a cornercorner with one As(1)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and corners with two equivalent Fe(1)O5 trigonal bipyramids. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Fe(1), and one As(1) atom. In the second O site, O(2) is bonded in a T-shaped geometry to one Mg(1), one Fe(1), and one As(1) atom. In the third O site, O(3) is bonded in a T-shaped geometry to one Mg(1), one Fe(1), and one As(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Fe(1) and one As(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Fe(1), and one As(2) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Mg(1) and one As(2) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to one As(1) and one As(2) atom.
MgFeAs2O7 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(6) atom to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one As(1)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra,  an edgeedge with one As(1)O4 tetrahedra, and edges with two equivalent Fe(1)O5 trigonal bipyramids. The Mg(1)-O(1) bond length is 2.06 Å. The Mg(1)-O(2) bond length is 2.16 Å. The Mg(1)-O(3) bond length is 2.09 Å. The Mg(1)-O(5) bond length is 1.99 Å. The Mg(1)-O(6) bond length is 1.97 Å. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(5) atom to form distorted FeO5 trigonal bipyramids that share corners with two equivalent As(2)O4 tetrahedra, corners with three equivalent As(1)O4 tetrahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The Fe(1)-O(1) bond length is 2.11 Å. The Fe(1)-O(2) bond length is 2.19 Å. The Fe(1)-O(3) bond length is 2.08 Å. The Fe(1)-O(4) bond length is 1.99 Å. The Fe(1)-O(5) bond length is 2.20 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form AsO4 tetrahedra that share  a cornercorner with one As(2)O4 tetrahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, corners with three equivalent Fe(1)O5 trigonal bipyramids, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The As(1)-O(1) bond length is 1.72 Å. The As(1)-O(2) bond length is 1.70 Å. The As(1)-O(3) bond length is 1.72 Å. The As(1)-O(7) bond length is 1.78 Å. In the second As site, As(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form AsO4 tetrahedra that share  a cornercorner with one As(1)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and corners with two equivalent Fe(1)O5 trigonal bipyramids. The As(2)-O(4) bond length is 1.69 Å. The As(2)-O(5) bond length is 1.72 Å. The As(2)-O(6) bond length is 1.68 Å. The As(2)-O(7) bond length is 1.83 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Fe(1), and one As(1) atom. In the second O site, O(2) is bonded in a T-shaped geometry to one Mg(1), one Fe(1), and one As(1) atom. In the third O site, O(3) is bonded in a T-shaped geometry to one Mg(1), one Fe(1), and one As(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Fe(1) and one As(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Fe(1), and one As(2) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Mg(1) and one As(2) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to one As(1) and one As(2) atom.