Na3Cu2O4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(2) and three equivalent O(1) atoms to form distorted NaO4 tetrahedra that share  a cornercorner with one Na(2)O6 octahedra, corners with two equivalent Na(1)O4 tetrahedra, edges with two equivalent Na(2)O6 octahedra, and edges with two equivalent Na(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 29°. In the second Na site, Na(2) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form distorted NaO6 octahedra that share corners with two equivalent Na(1)O4 tetrahedra, edges with two equivalent Na(2)O6 octahedra, and edges with four equivalent Na(1)O4 tetrahedra. Cu(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to one Na(2), three equivalent Na(1), and two equivalent Cu(1) atoms. In the second O site, O(2) is bonded to one Na(1), two equivalent Na(2), and two equivalent Cu(1) atoms to form a mixture of edge and corner-sharing ONa3Cu2 square pyramids.
Na3Cu2O4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(2) and three equivalent O(1) atoms to form distorted NaO4 tetrahedra that share  a cornercorner with one Na(2)O6 octahedra, corners with two equivalent Na(1)O4 tetrahedra, edges with two equivalent Na(2)O6 octahedra, and edges with two equivalent Na(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 29°. The Na(1)-O(2) bond length is 2.26 Å. There are two shorter (2.29 Å) and one longer (2.35 Å) Na(1)-O(1) bond length. In the second Na site, Na(2) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form distorted NaO6 octahedra that share corners with two equivalent Na(1)O4 tetrahedra, edges with two equivalent Na(2)O6 octahedra, and edges with four equivalent Na(1)O4 tetrahedra. Both Na(2)-O(1) bond lengths are 2.84 Å. All Na(2)-O(2) bond lengths are 2.34 Å. Cu(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Cu(1)-O(1) bond lengths are 1.93 Å. Both Cu(1)-O(2) bond lengths are 1.92 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to one Na(2), three equivalent Na(1), and two equivalent Cu(1) atoms. In the second O site, O(2) is bonded to one Na(1), two equivalent Na(2), and two equivalent Cu(1) atoms to form a mixture of edge and corner-sharing ONa3Cu2 square pyramids.