Cr2P2O9 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(3), one O(4), one O(6), one O(7), and two equivalent O(5) atoms to form CrO6 octahedra that share corners with two equivalent Cr(2)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. In the second Cr site, Cr(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CrO6 octahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and edges with two equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles are 50°. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(6), and two equivalent O(5) atoms to form PO4 tetrahedra that share corners with two equivalent Cr(2)O6 octahedra and corners with three equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-53°. In the second P site, P(2) is bonded to one O(4), one O(7), and two equivalent O(1) atoms to form PO4 tetrahedra that share corners with two equivalent Cr(2)O6 octahedra and  an edgeedge with one Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles are 48°. There are seven inequivalent O sites. In the first O site, O(4) is bonded in an L-shaped geometry to one Cr(1) and one P(2) atom. In the second O site, O(5) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(1) atom. In the third O site, O(6) is bonded in a linear geometry to one Cr(1) and one P(1) atom. In the fourth O site, O(7) is bonded in an L-shaped geometry to one Cr(1) and one P(2) atom. In the fifth O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Cr(2) and one P(2) atom. In the sixth O site, O(2) is bonded in a trigonal planar geometry to two equivalent Cr(2) and one P(1) atom. In the seventh O site, O(3) is bonded in a distorted trigonal planar geometry to one Cr(1) and two equivalent Cr(2) atoms.
Cr2P2O9 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(3), one O(4), one O(6), one O(7), and two equivalent O(5) atoms to form CrO6 octahedra that share corners with two equivalent Cr(2)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. The Cr(1)-O(3) bond length is 1.85 Å. The Cr(1)-O(4) bond length is 1.98 Å. The Cr(1)-O(6) bond length is 1.89 Å. The Cr(1)-O(7) bond length is 2.04 Å. Both Cr(1)-O(5) bond lengths are 1.94 Å. In the second Cr site, Cr(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CrO6 octahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and edges with two equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles are 50°. Both Cr(2)-O(1) bond lengths are 1.95 Å. Both Cr(2)-O(2) bond lengths are 2.03 Å. Both Cr(2)-O(3) bond lengths are 2.06 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(6), and two equivalent O(5) atoms to form PO4 tetrahedra that share corners with two equivalent Cr(2)O6 octahedra and corners with three equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-53°. The P(1)-O(2) bond length is 1.59 Å. The P(1)-O(6) bond length is 1.54 Å. Both P(1)-O(5) bond lengths are 1.52 Å. In the second P site, P(2) is bonded to one O(4), one O(7), and two equivalent O(1) atoms to form PO4 tetrahedra that share corners with two equivalent Cr(2)O6 octahedra and  an edgeedge with one Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles are 48°. The P(2)-O(4) bond length is 1.56 Å. The P(2)-O(7) bond length is 1.56 Å. Both P(2)-O(1) bond lengths are 1.54 Å. There are seven inequivalent O sites. In the first O site, O(4) is bonded in an L-shaped geometry to one Cr(1) and one P(2) atom. In the second O site, O(5) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(1) atom. In the third O site, O(6) is bonded in a linear geometry to one Cr(1) and one P(1) atom. In the fourth O site, O(7) is bonded in an L-shaped geometry to one Cr(1) and one P(2) atom. In the fifth O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Cr(2) and one P(2) atom. In the sixth O site, O(2) is bonded in a trigonal planar geometry to two equivalent Cr(2) and one P(1) atom. In the seventh O site, O(3) is bonded in a distorted trigonal planar geometry to one Cr(1) and two equivalent Cr(2) atoms.