CaFe3(P2O7)2 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), one O(5), one O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra, and  an edgeedge with one Fe(2)O6 octahedra. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra, corners with four equivalent P(2)O4 tetrahedra, and edges with two equivalent Fe(1)O6 octahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with three equivalent Fe(1)O6 octahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-62°. In the second P site, P(2) is bonded to one O(1), one O(4), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Fe(2)O6 octahedra, corners with three equivalent Fe(1)O6 octahedra, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 40-59°. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Fe(1), and one P(1) atom. In the second O site, O(6) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(2) atom. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent Fe(1) and one P(2) atom. In the fourth O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1), one Fe(2), and one P(2) atom. In the fifth O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), one Fe(1), one Fe(2), and one P(1) atom. In the sixth O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Fe(1), and one P(1) atom. In the seventh O site, O(4) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom.
CaFe3(P2O7)2 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. Both Ca(1)-O(1) bond lengths are 2.49 Å. Both Ca(1)-O(2) bond lengths are 2.56 Å. Both Ca(1)-O(3) bond lengths are 2.59 Å. Both Ca(1)-O(5) bond lengths are 2.74 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), one O(5), one O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  an edgeedge with one Fe(1)O6 octahedra, and  an edgeedge with one Fe(2)O6 octahedra. The Fe(1)-O(2) bond length is 2.26 Å. The Fe(1)-O(3) bond length is 2.23 Å. The Fe(1)-O(5) bond length is 2.10 Å. The Fe(1)-O(6) bond length is 2.17 Å. There is one shorter (2.13 Å) and one longer (2.14 Å) Fe(1)-O(7) bond length. In the second Fe site, Fe(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra, corners with four equivalent P(2)O4 tetrahedra, and edges with two equivalent Fe(1)O6 octahedra. Both Fe(2)-O(1) bond lengths are 2.19 Å. Both Fe(2)-O(2) bond lengths are 2.21 Å. Both Fe(2)-O(6) bond lengths are 2.10 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with three equivalent Fe(1)O6 octahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-62°. The P(1)-O(2) bond length is 1.57 Å. The P(1)-O(3) bond length is 1.52 Å. The P(1)-O(4) bond length is 1.62 Å. The P(1)-O(5) bond length is 1.52 Å. In the second P site, P(2) is bonded to one O(1), one O(4), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Fe(2)O6 octahedra, corners with three equivalent Fe(1)O6 octahedra, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 40-59°. The P(2)-O(1) bond length is 1.53 Å. The P(2)-O(4) bond length is 1.61 Å. The P(2)-O(6) bond length is 1.54 Å. The P(2)-O(7) bond length is 1.53 Å. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), one Fe(1), and one P(1) atom. In the second O site, O(6) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one P(2) atom. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent Fe(1) and one P(2) atom. In the fourth O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1), one Fe(2), and one P(2) atom. In the fifth O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), one Fe(1), one Fe(2), and one P(1) atom. In the sixth O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Fe(1), and one P(1) atom. In the seventh O site, O(4) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom.