MnFe2(PO9)2 crystallizes in the monoclinic P2_1/c space group. Mn(1) is bonded to two equivalent O(3), two equivalent O(7), and two equivalent O(8) atoms to form distorted MnO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra. Fe(1) is bonded to one O(1), one O(2), one O(4), one O(6), and two equivalent O(5) atoms to form FeO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra and corners with three equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 36°. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one Mn(1)O6 octahedra and corners with three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-49°. There are nine inequivalent O sites. In the first O site, O(7) is bonded in a bent 120 degrees geometry to one Mn(1) and one O(9) atom. In the second O site, O(8) is bonded in a single-bond geometry to one Mn(1) atom. In the third O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(1) atom. In the fourth O site, O(9) is bonded in a single-bond geometry to one O(7) atom. In the fifth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the sixth O site, O(3) is bonded in a bent 120 degrees geometry to one Mn(1) and one P(1) atom. In the seventh O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the eighth O site, O(5) is bonded in a bent 150 degrees geometry to two equivalent Fe(1) atoms. In the ninth O site, O(6) is bonded in a single-bond geometry to one Fe(1) atom.
MnFe2(PO9)2 crystallizes in the monoclinic P2_1/c space group. Mn(1) is bonded to two equivalent O(3), two equivalent O(7), and two equivalent O(8) atoms to form distorted MnO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra. Both Mn(1)-O(3) bond lengths are 1.91 Å. Both Mn(1)-O(7) bond lengths are 2.53 Å. Both Mn(1)-O(8) bond lengths are 1.77 Å. Fe(1) is bonded to one O(1), one O(2), one O(4), one O(6), and two equivalent O(5) atoms to form FeO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra and corners with three equivalent P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 36°. The Fe(1)-O(1) bond length is 1.93 Å. The Fe(1)-O(2) bond length is 1.98 Å. The Fe(1)-O(4) bond length is 2.13 Å. The Fe(1)-O(6) bond length is 1.90 Å. There is one shorter (1.84 Å) and one longer (1.94 Å) Fe(1)-O(5) bond length. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one Mn(1)O6 octahedra and corners with three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 44-49°. The P(1)-O(1) bond length is 1.55 Å. The P(1)-O(2) bond length is 1.53 Å. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(4) bond length is 1.57 Å. There are nine inequivalent O sites. In the first O site, O(7) is bonded in a bent 120 degrees geometry to one Mn(1) and one O(9) atom. The O(7)-O(9) bond length is 1.23 Å. In the second O site, O(8) is bonded in a single-bond geometry to one Mn(1) atom. In the third O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(1) atom. In the fourth O site, O(9) is bonded in a single-bond geometry to one O(7) atom. In the fifth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the sixth O site, O(3) is bonded in a bent 120 degrees geometry to one Mn(1) and one P(1) atom. In the seventh O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Fe(1) and one P(1) atom. In the eighth O site, O(5) is bonded in a bent 150 degrees geometry to two equivalent Fe(1) atoms. In the ninth O site, O(6) is bonded in a single-bond geometry to one Fe(1) atom.