Na2MnO2 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 3-coordinate geometry to one O(2) and two equivalent O(4) atoms. In the second Na site, Na(2) is bonded in a distorted trigonal planar geometry to one O(1), one O(2), and one O(4) atom. In the third Na site, Na(3) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(4) atom. In the fourth Na site, Na(4) is bonded in a 4-coordinate geometry to one O(1), one O(3), and two equivalent O(2) atoms. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(4), and two equivalent O(3) atoms to form a mixture of distorted corner and edge-sharing MnO4 trigonal pyramids. In the second Mn site, Mn(2) is bonded to one O(3), one O(4), and two equivalent O(1) atoms to form a mixture of distorted corner and edge-sharing MnO4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(2), one Na(3), one Na(4), and two equivalent Mn(2) atoms. In the second O site, O(2) is bonded to one Na(1), one Na(2), one Na(3), two equivalent Na(4), and one Mn(1) atom to form ONa5Mn octahedra that share corners with two equivalent O(2)Na5Mn octahedra, corners with three equivalent O(4)Na4Mn2 octahedra, and  an edgeedge with one O(4)Na4Mn2 octahedra. The corner-sharing octahedral tilt angles range from 41-50°. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(3), one Na(4), one Mn(2), and two equivalent Mn(1) atoms. In the fourth O site, O(4) is bonded to one Na(2), one Na(3), two equivalent Na(1), one Mn(1), and one Mn(2) atom to form ONa4Mn2 octahedra that share corners with two equivalent O(4)Na4Mn2 octahedra, corners with three equivalent O(2)Na5Mn octahedra, and  an edgeedge with one O(2)Na5Mn octahedra. The corner-sharing octahedral tilt angles range from 47-60°.
Na2MnO2 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 3-coordinate geometry to one O(2) and two equivalent O(4) atoms. The Na(1)-O(2) bond length is 2.29 Å. There is one shorter (2.29 Å) and one longer (2.40 Å) Na(1)-O(4) bond length. In the second Na site, Na(2) is bonded in a distorted trigonal planar geometry to one O(1), one O(2), and one O(4) atom. The Na(2)-O(1) bond length is 2.29 Å. The Na(2)-O(2) bond length is 2.41 Å. The Na(2)-O(4) bond length is 2.38 Å. In the third Na site, Na(3) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(4) atom. The Na(3)-O(1) bond length is 2.73 Å. The Na(3)-O(2) bond length is 2.51 Å. The Na(3)-O(3) bond length is 2.31 Å. The Na(3)-O(4) bond length is 2.60 Å. In the fourth Na site, Na(4) is bonded in a 4-coordinate geometry to one O(1), one O(3), and two equivalent O(2) atoms. The Na(4)-O(1) bond length is 2.36 Å. The Na(4)-O(3) bond length is 2.59 Å. There is one shorter (2.27 Å) and one longer (2.29 Å) Na(4)-O(2) bond length. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(4), and two equivalent O(3) atoms to form a mixture of distorted corner and edge-sharing MnO4 trigonal pyramids. The Mn(1)-O(2) bond length is 2.00 Å. The Mn(1)-O(4) bond length is 2.07 Å. There is one shorter (2.13 Å) and one longer (2.22 Å) Mn(1)-O(3) bond length. In the second Mn site, Mn(2) is bonded to one O(3), one O(4), and two equivalent O(1) atoms to form a mixture of distorted corner and edge-sharing MnO4 tetrahedra. The Mn(2)-O(3) bond length is 2.08 Å. The Mn(2)-O(4) bond length is 2.11 Å. There is one shorter (2.05 Å) and one longer (2.14 Å) Mn(2)-O(1) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(2), one Na(3), one Na(4), and two equivalent Mn(2) atoms. In the second O site, O(2) is bonded to one Na(1), one Na(2), one Na(3), two equivalent Na(4), and one Mn(1) atom to form ONa5Mn octahedra that share corners with two equivalent O(2)Na5Mn octahedra, corners with three equivalent O(4)Na4Mn2 octahedra, and  an edgeedge with one O(4)Na4Mn2 octahedra. The corner-sharing octahedral tilt angles range from 41-50°. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(3), one Na(4), one Mn(2), and two equivalent Mn(1) atoms. In the fourth O site, O(4) is bonded to one Na(2), one Na(3), two equivalent Na(1), one Mn(1), and one Mn(2) atom to form ONa4Mn2 octahedra that share corners with two equivalent O(4)Na4Mn2 octahedra, corners with three equivalent O(2)Na5Mn octahedra, and  an edgeedge with one O(2)Na5Mn octahedra. The corner-sharing octahedral tilt angles range from 47-60°.