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Na2Se is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Na1+ is bonded to four equivalent Se2- atoms to form a mixture of edge and corner-sharing NaSe4 tetrahedra. All Na–Se bond lengths are 2.97 Å. Se2- is bonded in a body-centered cubic geometry to eight equivalent Na1+ atoms.
NaSe2 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. there are two inequivalent Na sites. In the first Na site, Na is bonded to six Se atoms to form distorted corner-sharing NaSe6 pentagonal pyramids. There are a spread of Na–Se bond distances ranging from 2.96–3.24 Å. In the second Na site, Na is bonded in a 6-coordinate geometry to six Se atoms. There are a spread of Na–Se bond distances ranging from 2.97–3.27 Å. There are two inequivalent Se sites. In the first Se site, Se is bonded in a distorted see-saw-like geometry to two Na and two Se atoms. There are one shorter (2.39 Å) and one longer (2.41 Å) Se–Se bond lengths. In the second Se site, Se is bonded in a 5-coordinate geometry to four Na and one Se atom.
NaSe crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six equivalent Se1- atoms to form edge-sharing NaSe6 octahedra. All Na–Se bond lengths are 3.09 Å. In the second Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six equivalent Se1- atoms. All Na–Se bond lengths are 3.00 Å. Se1- is bonded in a 7-coordinate geometry to six Na1+ and one Se1- atom. The Se–Se bond length is 2.48 Å.