Na2U2O7 crystallizes in the monoclinic Pm space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 7-coordinate geometry to one O(2), one O(4), one O(6), two equivalent O(1), and two equivalent O(3) atoms. In the second Na site, Na(2) is bonded in a body-centered cubic geometry to one O(1), one O(3), one O(5), one O(7), two equivalent O(2), and two equivalent O(4) atoms. There are two inequivalent U sites. In the first U site, U(1) is bonded in a 7-coordinate geometry to one O(2), one O(4), one O(6), two equivalent O(5), and two equivalent O(7) atoms. In the second U site, U(2) is bonded to one O(1), one O(3), one O(5), one O(7), and two equivalent O(6) atoms to form distorted corner-sharing UO6 octahedra. The corner-sharing octahedral tilt angles are 43°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(2), two equivalent Na(1), and one U(2) atom. In the second O site, O(2) is bonded to one Na(1), two equivalent Na(2), and one U(1) atom to form distorted ONa3U tetrahedra that share corners with two equivalent O(2)Na3U tetrahedra, corners with four equivalent O(4)Na3U tetrahedra, corners with two equivalent O(6)NaU3 trigonal pyramids, corners with four equivalent O(7)NaU3 trigonal pyramids,  an edgeedge with one O(4)Na3U tetrahedra, edges with two equivalent O(3)Na3U tetrahedra, and edges with two equivalent O(5)NaU3 trigonal pyramids. In the third O site, O(3) is bonded to one Na(2), two equivalent Na(1), and one U(2) atom to form distorted ONa3U tetrahedra that share corners with two equivalent O(3)Na3U tetrahedra, corners with four equivalent O(4)Na3U tetrahedra, corners with two equivalent O(5)NaU3 trigonal pyramids, edges with two equivalent O(2)Na3U tetrahedra,  an edgeedge with one O(7)NaU3 trigonal pyramid, and edges with two equivalent O(6)NaU3 trigonal pyramids. In the fourth O site, O(4) is bonded to one Na(1), two equivalent Na(2), and one U(1) atom to form distorted ONa3U tetrahedra that share corners with two equivalent O(4)Na3U tetrahedra, corners with four equivalent O(2)Na3U tetrahedra, corners with four equivalent O(3)Na3U tetrahedra, corners with four equivalent O(5)NaU3 trigonal pyramids,  an edgeedge with one O(2)Na3U tetrahedra,  an edgeedge with one O(6)NaU3 trigonal pyramid, and edges with two equivalent O(7)NaU3 trigonal pyramids. In the fifth O site, O(5) is bonded to one Na(2), one U(2), and two equivalent U(1) atoms to form distorted ONaU3 trigonal pyramids that share corners with two equivalent O(3)Na3U tetrahedra, corners with four equivalent O(4)Na3U tetrahedra, corners with two equivalent O(5)NaU3 trigonal pyramids, corners with four equivalent O(7)NaU3 trigonal pyramids, edges with two equivalent O(2)Na3U tetrahedra,  an edgeedge with one O(7)NaU3 trigonal pyramid, and edges with two equivalent O(6)NaU3 trigonal pyramids. In the sixth O site, O(6) is bonded to one Na(1), one U(1), and two equivalent U(2) atoms to form distorted ONaU3 trigonal pyramids that share corners with two equivalent O(2)Na3U tetrahedra, corners with two equivalent O(6)NaU3 trigonal pyramids, corners with four equivalent O(7)NaU3 trigonal pyramids,  an edgeedge with one O(4)Na3U tetrahedra, edges with two equivalent O(3)Na3U tetrahedra, and edges with two equivalent O(5)NaU3 trigonal pyramids. In the seventh O site, O(7) is bonded to one Na(2), one U(2), and two equivalent U(1) atoms to form distorted ONaU3 trigonal pyramids that share corners with four equivalent O(2)Na3U tetrahedra, corners with two equivalent O(7)NaU3 trigonal pyramids, corners with four equivalent O(5)NaU3 trigonal pyramids, corners with four equivalent O(6)NaU3 trigonal pyramids,  an edgeedge with one O(3)Na3U tetrahedra, edges with two equivalent O(4)Na3U tetrahedra, and  an edgeedge with one O(5)NaU3 trigonal pyramid.
Na2U2O7 crystallizes in the monoclinic Pm space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 7-coordinate geometry to one O(2), one O(4), one O(6), two equivalent O(1), and two equivalent O(3) atoms. The Na(1)-O(2) bond length is 2.54 Å. The Na(1)-O(4) bond length is 2.49 Å. The Na(1)-O(6) bond length is 2.75 Å. Both Na(1)-O(1) bond lengths are 2.61 Å. Both Na(1)-O(3) bond lengths are 2.46 Å. In the second Na site, Na(2) is bonded in a body-centered cubic geometry to one O(1), one O(3), one O(5), one O(7), two equivalent O(2), and two equivalent O(4) atoms. The Na(2)-O(1) bond length is 2.71 Å. The Na(2)-O(3) bond length is 2.61 Å. The Na(2)-O(5) bond length is 2.79 Å. The Na(2)-O(7) bond length is 2.82 Å. Both Na(2)-O(2) bond lengths are 2.62 Å. Both Na(2)-O(4) bond lengths are 2.63 Å. There are two inequivalent U sites. In the first U site, U(1) is bonded in a 7-coordinate geometry to one O(2), one O(4), one O(6), two equivalent O(5), and two equivalent O(7) atoms. The U(1)-O(2) bond length is 1.87 Å. The U(1)-O(4) bond length is 1.87 Å. The U(1)-O(6) bond length is 2.50 Å. Both U(1)-O(5) bond lengths are 2.25 Å. Both U(1)-O(7) bond lengths are 2.48 Å. In the second U site, U(2) is bonded to one O(1), one O(3), one O(5), one O(7), and two equivalent O(6) atoms to form distorted corner-sharing UO6 octahedra. The corner-sharing octahedral tilt angles are 43°. The U(2)-O(1) bond length is 1.90 Å. The U(2)-O(3) bond length is 1.90 Å. The U(2)-O(5) bond length is 2.26 Å. The U(2)-O(7) bond length is 2.20 Å. Both U(2)-O(6) bond lengths are 2.14 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(2), two equivalent Na(1), and one U(2) atom. In the second O site, O(2) is bonded to one Na(1), two equivalent Na(2), and one U(1) atom to form distorted ONa3U tetrahedra that share corners with two equivalent O(2)Na3U tetrahedra, corners with four equivalent O(4)Na3U tetrahedra, corners with two equivalent O(6)NaU3 trigonal pyramids, corners with four equivalent O(7)NaU3 trigonal pyramids,  an edgeedge with one O(4)Na3U tetrahedra, edges with two equivalent O(3)Na3U tetrahedra, and edges with two equivalent O(5)NaU3 trigonal pyramids. In the third O site, O(3) is bonded to one Na(2), two equivalent Na(1), and one U(2) atom to form distorted ONa3U tetrahedra that share corners with two equivalent O(3)Na3U tetrahedra, corners with four equivalent O(4)Na3U tetrahedra, corners with two equivalent O(5)NaU3 trigonal pyramids, edges with two equivalent O(2)Na3U tetrahedra,  an edgeedge with one O(7)NaU3 trigonal pyramid, and edges with two equivalent O(6)NaU3 trigonal pyramids. In the fourth O site, O(4) is bonded to one Na(1), two equivalent Na(2), and one U(1) atom to form distorted ONa3U tetrahedra that share corners with two equivalent O(4)Na3U tetrahedra, corners with four equivalent O(2)Na3U tetrahedra, corners with four equivalent O(3)Na3U tetrahedra, corners with four equivalent O(5)NaU3 trigonal pyramids,  an edgeedge with one O(2)Na3U tetrahedra,  an edgeedge with one O(6)NaU3 trigonal pyramid, and edges with two equivalent O(7)NaU3 trigonal pyramids. In the fifth O site, O(5) is bonded to one Na(2), one U(2), and two equivalent U(1) atoms to form distorted ONaU3 trigonal pyramids that share corners with two equivalent O(3)Na3U tetrahedra, corners with four equivalent O(4)Na3U tetrahedra, corners with two equivalent O(5)NaU3 trigonal pyramids, corners with four equivalent O(7)NaU3 trigonal pyramids, edges with two equivalent O(2)Na3U tetrahedra,  an edgeedge with one O(7)NaU3 trigonal pyramid, and edges with two equivalent O(6)NaU3 trigonal pyramids. In the sixth O site, O(6) is bonded to one Na(1), one U(1), and two equivalent U(2) atoms to form distorted ONaU3 trigonal pyramids that share corners with two equivalent O(2)Na3U tetrahedra, corners with two equivalent O(6)NaU3 trigonal pyramids, corners with four equivalent O(7)NaU3 trigonal pyramids,  an edgeedge with one O(4)Na3U tetrahedra, edges with two equivalent O(3)Na3U tetrahedra, and edges with two equivalent O(5)NaU3 trigonal pyramids. In the seventh O site, O(7) is bonded to one Na(2), one U(2), and two equivalent U(1) atoms to form distorted ONaU3 trigonal pyramids that share corners with four equivalent O(2)Na3U tetrahedra, corners with two equivalent O(7)NaU3 trigonal pyramids, corners with four equivalent O(5)NaU3 trigonal pyramids, corners with four equivalent O(6)NaU3 trigonal pyramids,  an edgeedge with one O(3)Na3U tetrahedra, edges with two equivalent O(4)Na3U tetrahedra, and  an edgeedge with one O(5)NaU3 trigonal pyramid.