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Si3N2 is alpha Po structured and crystallizes in the cubic Pm-3m space group. The structure is zero-dimensional and consists of one Si3N2 cluster. Si+1.33+ is bonded in a bent 120 degrees geometry to two equivalent N2- atoms. Both Si–N bond lengths are 1.76 Å. N2- is bonded in a trigonal planar geometry to three equivalent Si+1.33+ atoms.
Si3N4 crystallizes in the hexagonal P6_3/m space group. The structure is three-dimensional. Si4+ is bonded to four N3- atoms to form corner-sharing SiN4 tetrahedra. There is one shorter (1.74 Å) and three longer (1.75 Å) Si–N bond length. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a trigonal planar geometry to three equivalent Si4+ atoms. In the second N3- site, N3- is bonded in a trigonal planar geometry to three equivalent Si4+ atoms.
Si2N3 crystallizes in the orthorhombic Cmc2_1 space group. The structure is three-dimensional. Si4+ is bonded to four N+2.67- atoms to form corner-sharing SiN4 tetrahedra. There are a spread of Si–N bond distances ranging from 1.68–1.76 Å. There are two inequivalent N+2.67- sites. In the first N+2.67- site, N+2.67- is bonded in a trigonal planar geometry to three equivalent Si4+ atoms. In the second N+2.67- site, N+2.67- is bonded in a bent 150 degrees geometry to two equivalent Si4+ atoms.