NaFeP2O7 crystallizes in the monoclinic P2_1 space group. Na(1) is bonded to one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form distorted NaO6 pentagonal pyramids that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, edges with two equivalent Fe(1)O6 octahedra,  an edgeedge with one P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 51°. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form FeO6 octahedra that share  a cornercorner with one Na(1)O6 pentagonal pyramid, corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and edges with two equivalent Na(1)O6 pentagonal pyramids. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra, corners with two equivalent Na(1)O6 pentagonal pyramids,  a cornercorner with one P(2)O4 tetrahedra, and  an edgeedge with one Na(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 38-49°. In the second P site, P(2) is bonded to one O(1), one O(2), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra,  a cornercorner with one Na(1)O6 pentagonal pyramid,  a cornercorner with one P(1)O4 tetrahedra, and  an edgeedge with one Na(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 23-49°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Na(1), one Fe(1), and one P(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Fe(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Na(1), one Fe(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Na(1), one Fe(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Fe(1), and one P(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Na(1), one P(1), and one P(2) atom.
NaFeP2O7 crystallizes in the monoclinic P2_1 space group. Na(1) is bonded to one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form distorted NaO6 pentagonal pyramids that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, edges with two equivalent Fe(1)O6 octahedra,  an edgeedge with one P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 51°. The Na(1)-O(2) bond length is 2.56 Å. The Na(1)-O(3) bond length is 2.30 Å. The Na(1)-O(4) bond length is 2.55 Å. The Na(1)-O(5) bond length is 2.32 Å. The Na(1)-O(6) bond length is 2.43 Å. The Na(1)-O(7) bond length is 2.57 Å. Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form FeO6 octahedra that share  a cornercorner with one Na(1)O6 pentagonal pyramid, corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and edges with two equivalent Na(1)O6 pentagonal pyramids. The Fe(1)-O(1) bond length is 2.02 Å. The Fe(1)-O(2) bond length is 2.02 Å. The Fe(1)-O(3) bond length is 2.01 Å. The Fe(1)-O(4) bond length is 2.07 Å. The Fe(1)-O(5) bond length is 2.07 Å. The Fe(1)-O(6) bond length is 2.01 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra, corners with two equivalent Na(1)O6 pentagonal pyramids,  a cornercorner with one P(2)O4 tetrahedra, and  an edgeedge with one Na(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 38-49°. The P(1)-O(3) bond length is 1.53 Å. The P(1)-O(4) bond length is 1.53 Å. The P(1)-O(5) bond length is 1.53 Å. The P(1)-O(7) bond length is 1.64 Å. In the second P site, P(2) is bonded to one O(1), one O(2), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra,  a cornercorner with one Na(1)O6 pentagonal pyramid,  a cornercorner with one P(1)O4 tetrahedra, and  an edgeedge with one Na(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 23-49°. The P(2)-O(1) bond length is 1.52 Å. The P(2)-O(2) bond length is 1.53 Å. The P(2)-O(6) bond length is 1.54 Å. The P(2)-O(7) bond length is 1.63 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Na(1), one Fe(1), and one P(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Fe(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Na(1), one Fe(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Na(1), one Fe(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Fe(1), and one P(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Na(1), one P(1), and one P(2) atom.