Na2CuP2O7 crystallizes in the monoclinic C2/c space group. Na(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form distorted NaO4 tetrahedra that share corners with four equivalent P(1)O4 tetrahedra and  an edgeedge with one Na(1)O4 tetrahedra. Cu(1) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(3) atoms. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra and corners with four equivalent Na(1)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Na(1) and one P(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Na(1), one Cu(1), and one P(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Na(1), one Cu(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to two equivalent P(1) atoms.
Na2CuP2O7 crystallizes in the monoclinic C2/c space group. Na(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form distorted NaO4 tetrahedra that share corners with four equivalent P(1)O4 tetrahedra and  an edgeedge with one Na(1)O4 tetrahedra. The Na(1)-O(2) bond length is 2.24 Å. The Na(1)-O(3) bond length is 2.23 Å. There is one shorter (2.26 Å) and one longer (2.27 Å) Na(1)-O(1) bond length. Cu(1) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(3) atoms. Both Cu(1)-O(2) bond lengths are 2.00 Å. Both Cu(1)-O(3) bond lengths are 1.95 Å. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra and corners with four equivalent Na(1)O4 tetrahedra. The P(1)-O(1) bond length is 1.51 Å. The P(1)-O(2) bond length is 1.54 Å. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(4) bond length is 1.64 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Na(1) and one P(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Na(1), one Cu(1), and one P(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Na(1), one Cu(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to two equivalent P(1) atoms.