Na5Ni9O16 crystallizes in the monoclinic P2/m space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted NaO6 octahedra that share corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Ni(4)O6 octahedra, corners with two equivalent Ni(5)O6 octahedra,  an edgeedge with one Na(2)O6 octahedra, edges with two equivalent Na(3)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-16°. In the second Na site, Na(2) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form distorted NaO6 octahedra that share corners with two equivalent Ni(5)O6 octahedra, corners with four equivalent Ni(3)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Ni(5)O6 octahedra, edges with four equivalent Na(3)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 13°. In the third Na site, Na(3) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form NaO6 octahedra that share corners with two equivalent Ni(2)O6 octahedra, corners with four equivalent Ni(1)O6 octahedra,  an edgeedge with one Na(3)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-14°. There are six inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with four equivalent Na(3)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra,  an edgeedge with one Ni(2)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Na(3)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-12°. In the second Ni site, Ni(2) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form NiO6 octahedra that share corners with two equivalent Na(3)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra,  an edgeedge with one Ni(2)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(4)O6 octahedra. The corner-sharing octahedral tilt angles are 14°. In the third Ni site, Ni(3) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with two equivalent Na(1)O6 octahedra, corners with two equivalent Na(2)O6 octahedra,  an edgeedge with one Ni(4)O6 octahedra,  an edgeedge with one Ni(5)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Na(3)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with two equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 13-16°. In the fourth Ni site, Ni(4) is bonded to two equivalent O(5) and four equivalent O(2) atoms to form NiO6 octahedra that share corners with four equivalent Na(1)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with four equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles are 14°. In the fifth Ni site, Ni(5) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form NiO6 octahedra that share corners with two equivalent Na(2)O6 octahedra, corners with four equivalent Na(1)O6 octahedra, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, edges with four equivalent Na(3)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-13°. In the sixth Ni site, Ni(6) is bonded in a 6-coordinate geometry to two equivalent O(5) and four equivalent O(2) atoms. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), one Na(2), one Na(3), one Ni(1), one Ni(3), and one Ni(5) atom to form ONa3Ni3 octahedra that share corners with four equivalent O(1)Na3Ni3 octahedra, corners with two equivalent O(2)NaNi4 square pyramids, edges with three equivalent O(1)Na3Ni3 octahedra, edges with four equivalent O(3)Na3Ni3 octahedra,  an edgeedge with one O(2)NaNi4 square pyramid, and edges with four equivalent O(4)Na2Ni3 square pyramids. The corner-sharing octahedral tilt angles range from 0-8°. In the second O site, O(2) is bonded to one Na(1), one Ni(2), one Ni(3), one Ni(4), and one Ni(6) atom to form ONaNi4 square pyramids that share corners with two equivalent O(1)Na3Ni3 octahedra, corners with two equivalent O(4)Na2Ni3 square pyramids, corners with three equivalent O(2)NaNi4 square pyramids,  an edgeedge with one O(1)Na3Ni3 octahedra, edges with two equivalent O(4)Na2Ni3 square pyramids, and edges with three equivalent O(2)NaNi4 square pyramids. The corner-sharing octahedral tilt angles are 3°. In the third O site, O(3) is bonded to one Na(2), two equivalent Na(3), one Ni(5), and two equivalent Ni(1) atoms to form ONa3Ni3 octahedra that share corners with two equivalent O(3)Na3Ni3 octahedra, corners with four equivalent O(4)Na2Ni3 square pyramids, edges with two equivalent O(3)Na3Ni3 octahedra, edges with eight equivalent O(1)Na3Ni3 octahedra, and edges with two equivalent O(4)Na2Ni3 square pyramids. The corner-sharing octahedra are not tilted. In the fourth O site, O(4) is bonded to one Na(1), one Na(3), one Ni(1), one Ni(2), and one Ni(3) atom to form ONa2Ni3 square pyramids that share corners with two equivalent O(3)Na3Ni3 octahedra, corners with two equivalent O(2)NaNi4 square pyramids, corners with three equivalent O(4)Na2Ni3 square pyramids,  an edgeedge with one O(3)Na3Ni3 octahedra, edges with four equivalent O(1)Na3Ni3 octahedra,  an edgeedge with one O(4)Na2Ni3 square pyramid, and edges with two equivalent O(2)NaNi4 square pyramids. The corner-sharing octahedral tilt angles range from 2-5°. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Ni(4), one Ni(6), and two equivalent Ni(2) atoms.
Na5Ni9O16 crystallizes in the monoclinic P2/m space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted NaO6 octahedra that share corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Ni(4)O6 octahedra, corners with two equivalent Ni(5)O6 octahedra,  an edgeedge with one Na(2)O6 octahedra, edges with two equivalent Na(3)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-16°. Both Na(1)-O(1) bond lengths are 2.37 Å. Both Na(1)-O(2) bond lengths are 2.28 Å. Both Na(1)-O(4) bond lengths are 2.28 Å. In the second Na site, Na(2) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form distorted NaO6 octahedra that share corners with two equivalent Ni(5)O6 octahedra, corners with four equivalent Ni(3)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Ni(5)O6 octahedra, edges with four equivalent Na(3)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 13°. Both Na(2)-O(3) bond lengths are 2.29 Å. All Na(2)-O(1) bond lengths are 2.26 Å. In the third Na site, Na(3) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form NaO6 octahedra that share corners with two equivalent Ni(2)O6 octahedra, corners with four equivalent Ni(1)O6 octahedra,  an edgeedge with one Na(3)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-14°. Both Na(3)-O(1) bond lengths are 2.34 Å. Both Na(3)-O(3) bond lengths are 2.39 Å. Both Na(3)-O(4) bond lengths are 2.31 Å. There are six inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with four equivalent Na(3)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra,  an edgeedge with one Ni(2)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Na(3)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-12°. Both Ni(1)-O(1) bond lengths are 2.02 Å. Both Ni(1)-O(3) bond lengths are 1.95 Å. Both Ni(1)-O(4) bond lengths are 1.93 Å. In the second Ni site, Ni(2) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form NiO6 octahedra that share corners with two equivalent Na(3)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra,  an edgeedge with one Ni(2)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(4)O6 octahedra. The corner-sharing octahedral tilt angles are 14°. Both Ni(2)-O(2) bond lengths are 1.91 Å. Both Ni(2)-O(4) bond lengths are 1.91 Å. Both Ni(2)-O(5) bond lengths are 1.89 Å. In the third Ni site, Ni(3) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with two equivalent Na(1)O6 octahedra, corners with two equivalent Na(2)O6 octahedra,  an edgeedge with one Ni(4)O6 octahedra,  an edgeedge with one Ni(5)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Na(3)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with two equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 13-16°. Both Ni(3)-O(1) bond lengths are 2.02 Å. Both Ni(3)-O(2) bond lengths are 2.10 Å. Both Ni(3)-O(4) bond lengths are 2.10 Å. In the fourth Ni site, Ni(4) is bonded to two equivalent O(5) and four equivalent O(2) atoms to form NiO6 octahedra that share corners with four equivalent Na(1)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with four equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles are 14°. Both Ni(4)-O(5) bond lengths are 2.20 Å. All Ni(4)-O(2) bond lengths are 1.94 Å. In the fifth Ni site, Ni(5) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form NiO6 octahedra that share corners with two equivalent Na(2)O6 octahedra, corners with four equivalent Na(1)O6 octahedra, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, edges with four equivalent Na(3)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-13°. Both Ni(5)-O(3) bond lengths are 2.08 Å. All Ni(5)-O(1) bond lengths are 1.94 Å. In the sixth Ni site, Ni(6) is bonded in a 6-coordinate geometry to two equivalent O(5) and four equivalent O(2) atoms. Both Ni(6)-O(5) bond lengths are 2.17 Å. All Ni(6)-O(2) bond lengths are 2.16 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), one Na(2), one Na(3), one Ni(1), one Ni(3), and one Ni(5) atom to form ONa3Ni3 octahedra that share corners with four equivalent O(1)Na3Ni3 octahedra, corners with two equivalent O(2)NaNi4 square pyramids, edges with three equivalent O(1)Na3Ni3 octahedra, edges with four equivalent O(3)Na3Ni3 octahedra,  an edgeedge with one O(2)NaNi4 square pyramid, and edges with four equivalent O(4)Na2Ni3 square pyramids. The corner-sharing octahedral tilt angles range from 0-8°. In the second O site, O(2) is bonded to one Na(1), one Ni(2), one Ni(3), one Ni(4), and one Ni(6) atom to form ONaNi4 square pyramids that share corners with two equivalent O(1)Na3Ni3 octahedra, corners with two equivalent O(4)Na2Ni3 square pyramids, corners with three equivalent O(2)NaNi4 square pyramids,  an edgeedge with one O(1)Na3Ni3 octahedra, edges with two equivalent O(4)Na2Ni3 square pyramids, and edges with three equivalent O(2)NaNi4 square pyramids. The corner-sharing octahedral tilt angles are 3°. In the third O site, O(3) is bonded to one Na(2), two equivalent Na(3), one Ni(5), and two equivalent Ni(1) atoms to form ONa3Ni3 octahedra that share corners with two equivalent O(3)Na3Ni3 octahedra, corners with four equivalent O(4)Na2Ni3 square pyramids, edges with two equivalent O(3)Na3Ni3 octahedra, edges with eight equivalent O(1)Na3Ni3 octahedra, and edges with two equivalent O(4)Na2Ni3 square pyramids. The corner-sharing octahedra are not tilted. In the fourth O site, O(4) is bonded to one Na(1), one Na(3), one Ni(1), one Ni(2), and one Ni(3) atom to form ONa2Ni3 square pyramids that share corners with two equivalent O(3)Na3Ni3 octahedra, corners with two equivalent O(2)NaNi4 square pyramids, corners with three equivalent O(4)Na2Ni3 square pyramids,  an edgeedge with one O(3)Na3Ni3 octahedra, edges with four equivalent O(1)Na3Ni3 octahedra,  an edgeedge with one O(4)Na2Ni3 square pyramid, and edges with two equivalent O(2)NaNi4 square pyramids. The corner-sharing octahedral tilt angles range from 2-5°. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Ni(4), one Ni(6), and two equivalent Ni(2) atoms.