FeMn2(PO4)3 crystallizes in the trigonal R-3c space group. Mn(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted MnO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and  a faceface with one Fe(1)O6 octahedra. Fe(1) is bonded to six equivalent O(2) atoms to form distorted FeO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and faces with two equivalent Mn(1)O6 octahedra. P(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra and corners with four equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 31-54°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Mn(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mn(1), one Fe(1), and one P(1) atom.
FeMn2(PO4)3 crystallizes in the trigonal R-3c space group. Mn(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted MnO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and  a faceface with one Fe(1)O6 octahedra. All Mn(1)-O(1) bond lengths are 1.97 Å. All Mn(1)-O(2) bond lengths are 2.12 Å. Fe(1) is bonded to six equivalent O(2) atoms to form distorted FeO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and faces with two equivalent Mn(1)O6 octahedra. All Fe(1)-O(2) bond lengths are 2.10 Å. P(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra and corners with four equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 31-54°. Both P(1)-O(1) bond lengths are 1.52 Å. Both P(1)-O(2) bond lengths are 1.58 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Mn(1) and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mn(1), one Fe(1), and one P(1) atom.