NaCo2O4 crystallizes in the orthorhombic Pmmn space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(1) atoms. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form edge-sharing CoO6 octahedra. In the second Co site, Co(2) is bonded to one O(2), one O(3), and four equivalent O(1) atoms to form edge-sharing CoO6 octahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), one Na(2), one Co(1), and two equivalent Co(2) atoms to form ONa2Co3 trigonal bipyramids that share corners with five equivalent O(1)Na2Co3 trigonal bipyramids, corners with two equivalent O(2)NaCo3 trigonal pyramids, corners with two equivalent O(3)NaCo3 trigonal pyramids, edges with four equivalent O(1)Na2Co3 trigonal bipyramids, edges with two equivalent O(2)NaCo3 trigonal pyramids, and edges with two equivalent O(3)NaCo3 trigonal pyramids. In the second O site, O(2) is bonded to one Na(2), one Co(2), and two equivalent Co(1) atoms to form ONaCo3 trigonal pyramids that share corners with four equivalent O(1)Na2Co3 trigonal bipyramids, corners with three equivalent O(2)NaCo3 trigonal pyramids, corners with three equivalent O(3)NaCo3 trigonal pyramids, edges with four equivalent O(1)Na2Co3 trigonal bipyramids, and  an edgeedge with one O(3)NaCo3 trigonal pyramid. In the third O site, O(3) is bonded to one Na(1), one Co(2), and two equivalent Co(1) atoms to form distorted ONaCo3 trigonal pyramids that share corners with four equivalent O(1)Na2Co3 trigonal bipyramids, corners with three equivalent O(2)NaCo3 trigonal pyramids, corners with three equivalent O(3)NaCo3 trigonal pyramids, edges with four equivalent O(1)Na2Co3 trigonal bipyramids, and  an edgeedge with one O(2)NaCo3 trigonal pyramid.
NaCo2O4 crystallizes in the orthorhombic Pmmn space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(1) atoms. Both Na(1)-O(3) bond lengths are 2.33 Å. All Na(1)-O(1) bond lengths are 2.43 Å. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Both Na(2)-O(2) bond lengths are 2.34 Å. All Na(2)-O(1) bond lengths are 2.43 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form edge-sharing CoO6 octahedra. Both Co(1)-O(1) bond lengths are 1.89 Å. Both Co(1)-O(2) bond lengths are 1.87 Å. Both Co(1)-O(3) bond lengths are 1.87 Å. In the second Co site, Co(2) is bonded to one O(2), one O(3), and four equivalent O(1) atoms to form edge-sharing CoO6 octahedra. The Co(2)-O(2) bond length is 1.87 Å. The Co(2)-O(3) bond length is 1.87 Å. There are two shorter (1.88 Å) and two longer (1.90 Å) Co(2)-O(1) bond lengths. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), one Na(2), one Co(1), and two equivalent Co(2) atoms to form ONa2Co3 trigonal bipyramids that share corners with five equivalent O(1)Na2Co3 trigonal bipyramids, corners with two equivalent O(2)NaCo3 trigonal pyramids, corners with two equivalent O(3)NaCo3 trigonal pyramids, edges with four equivalent O(1)Na2Co3 trigonal bipyramids, edges with two equivalent O(2)NaCo3 trigonal pyramids, and edges with two equivalent O(3)NaCo3 trigonal pyramids. In the second O site, O(2) is bonded to one Na(2), one Co(2), and two equivalent Co(1) atoms to form ONaCo3 trigonal pyramids that share corners with four equivalent O(1)Na2Co3 trigonal bipyramids, corners with three equivalent O(2)NaCo3 trigonal pyramids, corners with three equivalent O(3)NaCo3 trigonal pyramids, edges with four equivalent O(1)Na2Co3 trigonal bipyramids, and  an edgeedge with one O(3)NaCo3 trigonal pyramid. In the third O site, O(3) is bonded to one Na(1), one Co(2), and two equivalent Co(1) atoms to form distorted ONaCo3 trigonal pyramids that share corners with four equivalent O(1)Na2Co3 trigonal bipyramids, corners with three equivalent O(2)NaCo3 trigonal pyramids, corners with three equivalent O(3)NaCo3 trigonal pyramids, edges with four equivalent O(1)Na2Co3 trigonal bipyramids, and  an edgeedge with one O(2)NaCo3 trigonal pyramid.