Na4C2O5 crystallizes in the monoclinic Cm space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a square pyramidal geometry to one O(3), two equivalent O(1), and two equivalent O(2) atoms. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(2) atoms. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(3) and four equivalent O(1) atoms. In the fourth Na site, Na(4) is bonded in a 6-coordinate geometry to one C(1), one O(3), two equivalent O(1), and two equivalent O(2) atoms. There are two inequivalent C sites. In the first C site, C(1) is bonded in a bent 120 degrees geometry to one Na(4) and two equivalent O(1) atoms. In the second C site, C(2) is bonded in a trigonal planar geometry to one O(3) and two equivalent O(2) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 1-coordinate geometry to one Na(1), one Na(4), two equivalent Na(3), and one C(1) atom. In the second O site, O(2) is bonded in a 1-coordinate geometry to one Na(1), one Na(4), two equivalent Na(2), and one C(2) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to one Na(1), one Na(3), one Na(4), two equivalent Na(2), and one C(2) atom.
Na4C2O5 crystallizes in the monoclinic Cm space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a square pyramidal geometry to one O(3), two equivalent O(1), and two equivalent O(2) atoms. The Na(1)-O(3) bond length is 2.27 Å. Both Na(1)-O(1) bond lengths are 2.39 Å. Both Na(1)-O(2) bond lengths are 2.40 Å. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(2) atoms. Both Na(2)-O(3) bond lengths are 2.77 Å. There are two shorter (2.51 Å) and two longer (2.58 Å) Na(2)-O(2) bond lengths. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(3) and four equivalent O(1) atoms. The Na(3)-O(3) bond length is 2.64 Å. There are two shorter (2.49 Å) and two longer (2.62 Å) Na(3)-O(1) bond lengths. In the fourth Na site, Na(4) is bonded in a 6-coordinate geometry to one C(1), one O(3), two equivalent O(1), and two equivalent O(2) atoms. The Na(4)-C(1) bond length is 2.90 Å. The Na(4)-O(3) bond length is 2.52 Å. Both Na(4)-O(1) bond lengths are 2.38 Å. Both Na(4)-O(2) bond lengths are 2.30 Å. There are two inequivalent C sites. In the first C site, C(1) is bonded in a bent 120 degrees geometry to one Na(4) and two equivalent O(1) atoms. Both C(1)-O(1) bond lengths are 1.31 Å. In the second C site, C(2) is bonded in a trigonal planar geometry to one O(3) and two equivalent O(2) atoms. The C(2)-O(3) bond length is 1.29 Å. Both C(2)-O(2) bond lengths are 1.30 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 1-coordinate geometry to one Na(1), one Na(4), two equivalent Na(3), and one C(1) atom. In the second O site, O(2) is bonded in a 1-coordinate geometry to one Na(1), one Na(4), two equivalent Na(2), and one C(2) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to one Na(1), one Na(3), one Na(4), two equivalent Na(2), and one C(2) atom.