Si3N4 crystallizes in the trigonal P31c space group. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted see-saw-like geometry to two equivalent N(1) and two equivalent N(2) atoms. In the second Si site, Si(2) is bonded to one N(1), one N(3), one N(4), and two equivalent N(2) atoms to form a mixture of distorted edge and corner-sharing SiN5 trigonal bipyramids. There are four inequivalent N sites. In the first N site, N(1) is bonded in a distorted trigonal planar geometry to one Si(2) and two equivalent Si(1) atoms. In the second N site, N(2) is bonded to two equivalent Si(1) and two equivalent Si(2) atoms to form distorted corner-sharing NSi4 trigonal pyramids. In the third N site, N(3) is bonded in a 4-coordinate geometry to three equivalent Si(2) and one N(4) atom. In the fourth N site, N(4) is bonded in a 4-coordinate geometry to three equivalent Si(2) and one N(3) atom.
Si3N4 crystallizes in the trigonal P31c space group. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted see-saw-like geometry to two equivalent N(1) and two equivalent N(2) atoms. Both Si(1)-N(1) bond lengths are 1.82 Å. There is one shorter (1.79 Å) and one longer (2.12 Å) Si(1)-N(2) bond length. In the second Si site, Si(2) is bonded to one N(1), one N(3), one N(4), and two equivalent N(2) atoms to form a mixture of distorted edge and corner-sharing SiN5 trigonal bipyramids. The Si(2)-N(1) bond length is 1.77 Å. The Si(2)-N(3) bond length is 1.82 Å. The Si(2)-N(4) bond length is 1.83 Å. There is one shorter (1.85 Å) and one longer (1.94 Å) Si(2)-N(2) bond length. There are four inequivalent N sites. In the first N site, N(1) is bonded in a distorted trigonal planar geometry to one Si(2) and two equivalent Si(1) atoms. In the second N site, N(2) is bonded to two equivalent Si(1) and two equivalent Si(2) atoms to form distorted corner-sharing NSi4 trigonal pyramids. In the third N site, N(3) is bonded in a 4-coordinate geometry to three equivalent Si(2) and one N(4) atom. The N(3)-N(4) bond length is 1.27 Å. In the fourth N site, N(4) is bonded in a 4-coordinate geometry to three equivalent Si(2) and one N(3) atom.