Na5Co2O5 crystallizes in the monoclinic C2/c space group. There are five inequivalent Na sites. In the first Na site, Na(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(5), and two equivalent O(3) atoms. In the second Na site, Na(2) is bonded to one O(5), two equivalent O(1), and two equivalent O(4) atoms to form distorted NaO5 trigonal bipyramids that share corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Na(4)O4 trigonal pyramids, corners with two equivalent Na(5)O4 trigonal pyramids,  an edgeedge with one Co(1)O4 tetrahedra, edges with two equivalent Na(2)O5 trigonal bipyramids, and edges with two equivalent Na(5)O4 trigonal pyramids. In the third Na site, Na(3) is bonded in a 4-coordinate geometry to one O(3), one O(4), and two equivalent O(5) atoms. In the fourth Na site, Na(4) is bonded to one O(3), one O(4), and two equivalent O(2) atoms to form NaO4 trigonal pyramids that share corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Na(2)O5 trigonal bipyramids, corners with two equivalent Na(5)O4 trigonal pyramids, and  an edgeedge with one Na(4)O4 trigonal pyramid. In the fifth Na site, Na(5) is bonded to one O(3), one O(4), and two equivalent O(1) atoms to form distorted NaO4 trigonal pyramids that share corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Na(2)O5 trigonal bipyramids, corners with two equivalent Na(4)O4 trigonal pyramids, edges with two equivalent Na(2)O5 trigonal bipyramids, and  an edgeedge with one Na(5)O4 trigonal pyramid. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(2), and two equivalent O(5) atoms to form distorted CoO4 tetrahedra that share corners with two equivalent Na(2)O5 trigonal bipyramids, corners with two equivalent Na(4)O4 trigonal pyramids, corners with two equivalent Na(5)O4 trigonal pyramids,  an edgeedge with one Co(1)O4 tetrahedra, and  an edgeedge with one Na(2)O5 trigonal bipyramid. In the second Co site, Co(2) is bonded in a distorted trigonal planar geometry to one O(2), one O(3), and one O(4) atom. There are five inequivalent O sites. In the first O site, O(5) is bonded to one Na(1), one Na(2), two equivalent Na(3), and two equivalent Co(1) atoms to form distorted ONa4Co2 octahedra that share corners with four equivalent O(3)Na5Co octahedra, edges with two equivalent O(5)Na4Co2 octahedra, and edges with two equivalent O(4)Na5Co octahedra. The corner-sharing octahedral tilt angles range from 42-67°. In the second O site, O(1) is bonded in a 6-coordinate geometry to one Na(1), two equivalent Na(2), two equivalent Na(5), and one Co(1) atom. In the third O site, O(2) is bonded in a 5-coordinate geometry to one Na(1), two equivalent Na(4), one Co(1), and one Co(2) atom. In the fourth O site, O(3) is bonded to one Na(3), one Na(4), one Na(5), two equivalent Na(1), and one Co(2) atom to form distorted ONa5Co octahedra that share corners with four equivalent O(5)Na4Co2 octahedra, corners with four equivalent O(4)Na5Co octahedra, and  an edgeedge with one O(3)Na5Co octahedra. The corner-sharing octahedral tilt angles range from 42-67°. In the fifth O site, O(4) is bonded to one Na(3), one Na(4), one Na(5), two equivalent Na(2), and one Co(2) atom to form ONa5Co octahedra that share corners with four equivalent O(3)Na5Co octahedra,  an edgeedge with one O(4)Na5Co octahedra, and edges with two equivalent O(5)Na4Co2 octahedra. The corner-sharing octahedral tilt angles range from 42-55°.
Na5Co2O5 crystallizes in the monoclinic C2/c space group. There are five inequivalent Na sites. In the first Na site, Na(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(5), and two equivalent O(3) atoms. The Na(1)-O(1) bond length is 2.80 Å. The Na(1)-O(2) bond length is 2.45 Å. The Na(1)-O(5) bond length is 2.56 Å. There is one shorter (2.40 Å) and one longer (2.44 Å) Na(1)-O(3) bond length. In the second Na site, Na(2) is bonded to one O(5), two equivalent O(1), and two equivalent O(4) atoms to form distorted NaO5 trigonal bipyramids that share corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Na(4)O4 trigonal pyramids, corners with two equivalent Na(5)O4 trigonal pyramids,  an edgeedge with one Co(1)O4 tetrahedra, edges with two equivalent Na(2)O5 trigonal bipyramids, and edges with two equivalent Na(5)O4 trigonal pyramids. The Na(2)-O(5) bond length is 2.54 Å. There is one shorter (2.40 Å) and one longer (2.49 Å) Na(2)-O(1) bond length. There is one shorter (2.36 Å) and one longer (2.40 Å) Na(2)-O(4) bond length. In the third Na site, Na(3) is bonded in a 4-coordinate geometry to one O(3), one O(4), and two equivalent O(5) atoms. The Na(3)-O(3) bond length is 2.50 Å. The Na(3)-O(4) bond length is 2.42 Å. There is one shorter (2.35 Å) and one longer (2.36 Å) Na(3)-O(5) bond length. In the fourth Na site, Na(4) is bonded to one O(3), one O(4), and two equivalent O(2) atoms to form NaO4 trigonal pyramids that share corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Na(2)O5 trigonal bipyramids, corners with two equivalent Na(5)O4 trigonal pyramids, and  an edgeedge with one Na(4)O4 trigonal pyramid. The Na(4)-O(3) bond length is 2.39 Å. The Na(4)-O(4) bond length is 2.38 Å. There is one shorter (2.36 Å) and one longer (2.39 Å) Na(4)-O(2) bond length. In the fifth Na site, Na(5) is bonded to one O(3), one O(4), and two equivalent O(1) atoms to form distorted NaO4 trigonal pyramids that share corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Na(2)O5 trigonal bipyramids, corners with two equivalent Na(4)O4 trigonal pyramids, edges with two equivalent Na(2)O5 trigonal bipyramids, and  an edgeedge with one Na(5)O4 trigonal pyramid. The Na(5)-O(3) bond length is 2.40 Å. The Na(5)-O(4) bond length is 2.33 Å. There is one shorter (2.33 Å) and one longer (2.45 Å) Na(5)-O(1) bond length. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(2), and two equivalent O(5) atoms to form distorted CoO4 tetrahedra that share corners with two equivalent Na(2)O5 trigonal bipyramids, corners with two equivalent Na(4)O4 trigonal pyramids, corners with two equivalent Na(5)O4 trigonal pyramids,  an edgeedge with one Co(1)O4 tetrahedra, and  an edgeedge with one Na(2)O5 trigonal bipyramid. The Co(1)-O(1) bond length is 1.80 Å. The Co(1)-O(2) bond length is 1.85 Å. There is one shorter (1.94 Å) and one longer (1.97 Å) Co(1)-O(5) bond length. In the second Co site, Co(2) is bonded in a distorted trigonal planar geometry to one O(2), one O(3), and one O(4) atom. The Co(2)-O(2) bond length is 2.00 Å. The Co(2)-O(3) bond length is 1.81 Å. The Co(2)-O(4) bond length is 1.82 Å. There are five inequivalent O sites. In the first O site, O(5) is bonded to one Na(1), one Na(2), two equivalent Na(3), and two equivalent Co(1) atoms to form distorted ONa4Co2 octahedra that share corners with four equivalent O(3)Na5Co octahedra, edges with two equivalent O(5)Na4Co2 octahedra, and edges with two equivalent O(4)Na5Co octahedra. The corner-sharing octahedral tilt angles range from 42-67°. In the second O site, O(1) is bonded in a 6-coordinate geometry to one Na(1), two equivalent Na(2), two equivalent Na(5), and one Co(1) atom. In the third O site, O(2) is bonded in a 5-coordinate geometry to one Na(1), two equivalent Na(4), one Co(1), and one Co(2) atom. In the fourth O site, O(3) is bonded to one Na(3), one Na(4), one Na(5), two equivalent Na(1), and one Co(2) atom to form distorted ONa5Co octahedra that share corners with four equivalent O(5)Na4Co2 octahedra, corners with four equivalent O(4)Na5Co octahedra, and  an edgeedge with one O(3)Na5Co octahedra. The corner-sharing octahedral tilt angles range from 42-67°. In the fifth O site, O(4) is bonded to one Na(3), one Na(4), one Na(5), two equivalent Na(2), and one Co(2) atom to form ONa5Co octahedra that share corners with four equivalent O(3)Na5Co octahedra,  an edgeedge with one O(4)Na5Co octahedra, and edges with two equivalent O(5)Na4Co2 octahedra. The corner-sharing octahedral tilt angles range from 42-55°.