FeAs2O7 crystallizes in the monoclinic C2 space group. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share corners with six equivalent As(1)O4 tetrahedra. 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 Fe(1)O6 octahedra and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 23-54°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Fe(1) and one As(1) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to one Fe(1) and one As(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Fe(1) and one As(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to two equivalent As(1) atoms.
FeAs2O7 crystallizes in the monoclinic C2 space group. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share corners with six equivalent As(1)O4 tetrahedra. Both Fe(1)-O(1) bond lengths are 2.01 Å. Both Fe(1)-O(2) bond lengths are 1.99 Å. Both Fe(1)-O(3) bond lengths are 1.98 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 Fe(1)O6 octahedra and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 23-54°. The As(1)-O(1) bond length is 1.71 Å. The As(1)-O(2) bond length is 1.72 Å. The As(1)-O(3) bond length is 1.69 Å. The As(1)-O(4) bond length is 1.78 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Fe(1) and one As(1) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to one Fe(1) and one As(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Fe(1) and one As(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to two equivalent As(1) atoms.