Na5NbO5 crystallizes in the monoclinic C2/c space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form distorted NaO4 trigonal pyramids that share corners with four equivalent Na(2)O5 square pyramids, corners with two equivalent Na(3)O5 trigonal bipyramids, corners with two equivalent Nb(1)O5 trigonal bipyramids,  a cornercorner with one Na(1)O4 trigonal pyramid, edges with two equivalent Na(2)O5 square pyramids,  an edgeedge with one Na(3)O5 trigonal bipyramid,  an edgeedge with one Nb(1)O5 trigonal bipyramid, and  an edgeedge with one Na(1)O4 trigonal pyramid. In the second Na site, Na(2) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted NaO5 square pyramids that share  a cornercorner with one Na(2)O5 square pyramid,  a cornercorner with one Na(3)O5 trigonal bipyramid, corners with three equivalent Nb(1)O5 trigonal bipyramids, corners with four equivalent Na(1)O4 trigonal pyramids, edges with two equivalent Na(2)O5 square pyramids,  an edgeedge with one Nb(1)O5 trigonal bipyramid, edges with two equivalent Na(3)O5 trigonal bipyramids, and edges with two equivalent Na(1)O4 trigonal pyramids. In the third Na site, Na(3) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted NaO5 trigonal bipyramids that share corners with two equivalent Na(2)O5 square pyramids,  a cornercorner with one Nb(1)O5 trigonal bipyramid, corners with four equivalent Na(1)O4 trigonal pyramids, edges with four equivalent Na(2)O5 square pyramids, edges with two equivalent Nb(1)O5 trigonal bipyramids, and edges with two equivalent Na(1)O4 trigonal pyramids. Nb(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form NbO5 trigonal bipyramids that share corners with six equivalent Na(2)O5 square pyramids,  a cornercorner with one Na(3)O5 trigonal bipyramid, corners with four equivalent Na(1)O4 trigonal pyramids, edges with two equivalent Na(2)O5 square pyramids, edges with two equivalent Na(3)O5 trigonal bipyramids, and edges with two equivalent Na(1)O4 trigonal pyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Na(3), two equivalent Na(1), two equivalent Na(2), and one Nb(1) atom to form distorted ONa5Nb octahedra that share corners with four equivalent O(3)Na5Nb octahedra, corners with two equivalent O(2)Na4Nb square pyramids, edges with four equivalent O(3)Na5Nb octahedra, and edges with four equivalent O(2)Na4Nb square pyramids. The corner-sharing octahedral tilt angles range from 16-30°. In the second O site, O(2) is bonded to one Na(1), one Na(3), two equivalent Na(2), and one Nb(1) atom to form distorted ONa4Nb square pyramids that share  a cornercorner with one O(1)Na5Nb octahedra, corners with two equivalent O(3)Na5Nb octahedra, corners with two equivalent O(2)Na4Nb square pyramids, edges with two equivalent O(1)Na5Nb octahedra, edges with four equivalent O(3)Na5Nb octahedra, and  an edgeedge with one O(2)Na4Nb square pyramid. The corner-sharing octahedral tilt angles range from 30-68°. In the third O site, O(3) is bonded to one Na(3), two equivalent Na(1), two equivalent Na(2), and one Nb(1) atom to form distorted ONa5Nb octahedra that share corners with two equivalent O(1)Na5Nb octahedra, corners with two equivalent O(3)Na5Nb octahedra, corners with two equivalent O(2)Na4Nb square pyramids, edges with two equivalent O(1)Na5Nb octahedra, edges with two equivalent O(3)Na5Nb octahedra, and edges with four equivalent O(2)Na4Nb square pyramids. The corner-sharing octahedral tilt angles range from 9-32°.
Na5NbO5 crystallizes in the monoclinic C2/c space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form distorted NaO4 trigonal pyramids that share corners with four equivalent Na(2)O5 square pyramids, corners with two equivalent Na(3)O5 trigonal bipyramids, corners with two equivalent Nb(1)O5 trigonal bipyramids,  a cornercorner with one Na(1)O4 trigonal pyramid, edges with two equivalent Na(2)O5 square pyramids,  an edgeedge with one Na(3)O5 trigonal bipyramid,  an edgeedge with one Nb(1)O5 trigonal bipyramid, and  an edgeedge with one Na(1)O4 trigonal pyramid. The Na(1)-O(1) bond length is 2.33 Å. The Na(1)-O(2) bond length is 2.28 Å. There is one shorter (2.27 Å) and one longer (2.39 Å) Na(1)-O(3) bond length. In the second Na site, Na(2) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted NaO5 square pyramids that share  a cornercorner with one Na(2)O5 square pyramid,  a cornercorner with one Na(3)O5 trigonal bipyramid, corners with three equivalent Nb(1)O5 trigonal bipyramids, corners with four equivalent Na(1)O4 trigonal pyramids, edges with two equivalent Na(2)O5 square pyramids,  an edgeedge with one Nb(1)O5 trigonal bipyramid, edges with two equivalent Na(3)O5 trigonal bipyramids, and edges with two equivalent Na(1)O4 trigonal pyramids. The Na(2)-O(1) bond length is 2.44 Å. There is one shorter (2.32 Å) and one longer (2.40 Å) Na(2)-O(2) bond length. There is one shorter (2.32 Å) and one longer (2.39 Å) Na(2)-O(3) bond length. In the third Na site, Na(3) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted NaO5 trigonal bipyramids that share corners with two equivalent Na(2)O5 square pyramids,  a cornercorner with one Nb(1)O5 trigonal bipyramid, corners with four equivalent Na(1)O4 trigonal pyramids, edges with four equivalent Na(2)O5 square pyramids, edges with two equivalent Nb(1)O5 trigonal bipyramids, and edges with two equivalent Na(1)O4 trigonal pyramids. The Na(3)-O(1) bond length is 2.40 Å. Both Na(3)-O(2) bond lengths are 2.30 Å. Both Na(3)-O(3) bond lengths are 2.28 Å. Nb(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form NbO5 trigonal bipyramids that share corners with six equivalent Na(2)O5 square pyramids,  a cornercorner with one Na(3)O5 trigonal bipyramid, corners with four equivalent Na(1)O4 trigonal pyramids, edges with two equivalent Na(2)O5 square pyramids, edges with two equivalent Na(3)O5 trigonal bipyramids, and edges with two equivalent Na(1)O4 trigonal pyramids. The Nb(1)-O(1) bond length is 1.91 Å. Both Nb(1)-O(2) bond lengths are 1.94 Å. Both Nb(1)-O(3) bond lengths are 2.03 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Na(3), two equivalent Na(1), two equivalent Na(2), and one Nb(1) atom to form distorted ONa5Nb octahedra that share corners with four equivalent O(3)Na5Nb octahedra, corners with two equivalent O(2)Na4Nb square pyramids, edges with four equivalent O(3)Na5Nb octahedra, and edges with four equivalent O(2)Na4Nb square pyramids. The corner-sharing octahedral tilt angles range from 16-30°. In the second O site, O(2) is bonded to one Na(1), one Na(3), two equivalent Na(2), and one Nb(1) atom to form distorted ONa4Nb square pyramids that share  a cornercorner with one O(1)Na5Nb octahedra, corners with two equivalent O(3)Na5Nb octahedra, corners with two equivalent O(2)Na4Nb square pyramids, edges with two equivalent O(1)Na5Nb octahedra, edges with four equivalent O(3)Na5Nb octahedra, and  an edgeedge with one O(2)Na4Nb square pyramid. The corner-sharing octahedral tilt angles range from 30-68°. In the third O site, O(3) is bonded to one Na(3), two equivalent Na(1), two equivalent Na(2), and one Nb(1) atom to form distorted ONa5Nb octahedra that share corners with two equivalent O(1)Na5Nb octahedra, corners with two equivalent O(3)Na5Nb octahedra, corners with two equivalent O(2)Na4Nb square pyramids, edges with two equivalent O(1)Na5Nb octahedra, edges with two equivalent O(3)Na5Nb octahedra, and edges with four equivalent O(2)Na4Nb square pyramids. The corner-sharing octahedral tilt angles range from 9-32°.