NaCo2O3 crystallizes in the monoclinic P2_1 space group. Na(1) is bonded to one O(1), one O(2), and three equivalent O(3) atoms to form distorted NaO5 trigonal bipyramids that share corners with four equivalent Co(1)O4 tetrahedra, corners with four equivalent Co(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids,  an edgeedge with one Co(1)O4 tetrahedra,  an edgeedge with one Co(2)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form CoO4 tetrahedra that share corners with two equivalent Co(1)O4 tetrahedra, corners with five equivalent Co(2)O4 tetrahedra, corners with four equivalent Na(1)O5 trigonal bipyramids, and  an edgeedge with one Na(1)O5 trigonal bipyramid. In the second Co site, Co(2) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form CoO4 tetrahedra that share corners with two equivalent Co(2)O4 tetrahedra, corners with five equivalent Co(1)O4 tetrahedra, corners with four equivalent Na(1)O5 trigonal bipyramids, and  an edgeedge with one Na(1)O5 trigonal bipyramid. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), one Co(1), and two equivalent Co(2) atoms to form ONaCo3 tetrahedra that share corners with two equivalent O(1)NaCo3 tetrahedra, corners with five equivalent O(2)NaCo3 tetrahedra, corners with four equivalent O(3)Na3Co2 trigonal bipyramids, and  an edgeedge with one O(3)Na3Co2 trigonal bipyramid. In the second O site, O(2) is bonded to one Na(1), one Co(2), and two equivalent Co(1) atoms to form distorted ONaCo3 tetrahedra that share corners with two equivalent O(2)NaCo3 tetrahedra, corners with five equivalent O(1)NaCo3 tetrahedra, corners with four equivalent O(3)Na3Co2 trigonal bipyramids, and  an edgeedge with one O(3)Na3Co2 trigonal bipyramid. In the third O site, O(3) is bonded to three equivalent Na(1), one Co(1), and one Co(2) atom to form distorted ONa3Co2 trigonal bipyramids that share corners with four equivalent O(1)NaCo3 tetrahedra, corners with four equivalent O(2)NaCo3 tetrahedra, corners with two equivalent O(3)Na3Co2 trigonal bipyramids,  an edgeedge with one O(1)NaCo3 tetrahedra,  an edgeedge with one O(2)NaCo3 tetrahedra, and edges with two equivalent O(3)Na3Co2 trigonal bipyramids.
NaCo2O3 crystallizes in the monoclinic P2_1 space group. Na(1) is bonded to one O(1), one O(2), and three equivalent O(3) atoms to form distorted NaO5 trigonal bipyramids that share corners with four equivalent Co(1)O4 tetrahedra, corners with four equivalent Co(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids,  an edgeedge with one Co(1)O4 tetrahedra,  an edgeedge with one Co(2)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. The Na(1)-O(1) bond length is 2.34 Å. The Na(1)-O(2) bond length is 2.36 Å. There are a spread of Na(1)-O(3) bond distances ranging from 2.32-2.76 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form CoO4 tetrahedra that share corners with two equivalent Co(1)O4 tetrahedra, corners with five equivalent Co(2)O4 tetrahedra, corners with four equivalent Na(1)O5 trigonal bipyramids, and  an edgeedge with one Na(1)O5 trigonal bipyramid. The Co(1)-O(1) bond length is 1.98 Å. The Co(1)-O(3) bond length is 1.97 Å. There is one shorter (1.98 Å) and one longer (2.01 Å) Co(1)-O(2) bond length. In the second Co site, Co(2) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form CoO4 tetrahedra that share corners with two equivalent Co(2)O4 tetrahedra, corners with five equivalent Co(1)O4 tetrahedra, corners with four equivalent Na(1)O5 trigonal bipyramids, and  an edgeedge with one Na(1)O5 trigonal bipyramid. The Co(2)-O(2) bond length is 1.87 Å. The Co(2)-O(3) bond length is 1.81 Å. There is one shorter (1.93 Å) and one longer (1.96 Å) Co(2)-O(1) bond length. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), one Co(1), and two equivalent Co(2) atoms to form ONaCo3 tetrahedra that share corners with two equivalent O(1)NaCo3 tetrahedra, corners with five equivalent O(2)NaCo3 tetrahedra, corners with four equivalent O(3)Na3Co2 trigonal bipyramids, and  an edgeedge with one O(3)Na3Co2 trigonal bipyramid. In the second O site, O(2) is bonded to one Na(1), one Co(2), and two equivalent Co(1) atoms to form distorted ONaCo3 tetrahedra that share corners with two equivalent O(2)NaCo3 tetrahedra, corners with five equivalent O(1)NaCo3 tetrahedra, corners with four equivalent O(3)Na3Co2 trigonal bipyramids, and  an edgeedge with one O(3)Na3Co2 trigonal bipyramid. In the third O site, O(3) is bonded to three equivalent Na(1), one Co(1), and one Co(2) atom to form distorted ONa3Co2 trigonal bipyramids that share corners with four equivalent O(1)NaCo3 tetrahedra, corners with four equivalent O(2)NaCo3 tetrahedra, corners with two equivalent O(3)Na3Co2 trigonal bipyramids,  an edgeedge with one O(1)NaCo3 tetrahedra,  an edgeedge with one O(2)NaCo3 tetrahedra, and edges with two equivalent O(3)Na3Co2 trigonal bipyramids.