BaFe2(P2O7)2 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 12-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra and corners with four equivalent P(2)O4 tetrahedra. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra and corners with four equivalent P(1)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 27-47°. In the second P site, P(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 35-49°. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the second O site, O(5) is bonded in a bent 120 degrees geometry to one Ba(1), one P(1), and one P(2) atom. In the third O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Fe(2), and one P(2) atom. In the fourth O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Fe(2), and one P(1) atom. In the fifth O site, O(1) is bonded in a 2-coordinate geometry to one Ba(1), one Fe(2), and one P(1) atom. In the sixth O site, O(2) is bonded in a 3-coordinate geometry to one Ba(1), one Fe(1), and one P(2) atom. In the seventh O site, O(3) is bonded in a 2-coordinate geometry to one Ba(1), one Fe(1), and one P(1) atom.
BaFe2(P2O7)2 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 12-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. Both Ba(1)-O(1) bond lengths are 2.89 Å. Both Ba(1)-O(2) bond lengths are 2.82 Å. Both Ba(1)-O(3) bond lengths are 3.15 Å. Both Ba(1)-O(5) bond lengths are 3.41 Å. Both Ba(1)-O(6) bond lengths are 2.98 Å. Both Ba(1)-O(7) bond lengths are 2.96 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra and corners with four equivalent P(2)O4 tetrahedra. Both Fe(1)-O(2) bond lengths are 2.08 Å. Both Fe(1)-O(3) bond lengths are 2.06 Å. Both Fe(1)-O(4) bond lengths are 1.98 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra and corners with four equivalent P(1)O4 tetrahedra. Both Fe(2)-O(1) bond lengths are 2.05 Å. Both Fe(2)-O(6) bond lengths are 2.01 Å. Both Fe(2)-O(7) bond lengths are 2.02 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 27-47°. The P(1)-O(1) bond length is 1.53 Å. The P(1)-O(3) bond length is 1.53 Å. The P(1)-O(5) bond length is 1.63 Å. The P(1)-O(7) bond length is 1.52 Å. In the second P site, P(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 35-49°. The P(2)-O(2) bond length is 1.55 Å. The P(2)-O(4) bond length is 1.52 Å. The P(2)-O(5) bond length is 1.62 Å. The P(2)-O(6) bond length is 1.53 Å. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the second O site, O(5) is bonded in a bent 120 degrees geometry to one Ba(1), one P(1), and one P(2) atom. In the third O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Fe(2), and one P(2) atom. In the fourth O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Fe(2), and one P(1) atom. In the fifth O site, O(1) is bonded in a 2-coordinate geometry to one Ba(1), one Fe(2), and one P(1) atom. In the sixth O site, O(2) is bonded in a 3-coordinate geometry to one Ba(1), one Fe(1), and one P(2) atom. In the seventh O site, O(3) is bonded in a 2-coordinate geometry to one Ba(1), one Fe(1), and one P(1) atom.