# Polynitrides

Polynitrides are solid chemical compounds with a large amount of nitrogen, beyond what would be expected from valencies. Some with N$_2$ ions are termed pernitrides. Azides are not considered polynitrides, although pentazolates are.
They are formed at high pressures and mostly at high temperature. But some are stable when decompressed to standard conditions. They are high energy materials, capable of exploding with high power. Some are very hard, almost as strong as diamond.

## List

| formula | crystal | space group | unit cell | volume | density | at pressure | comment |
| LiN | | Cmcm | a = 3.819 b = 6.471 c = 3.446 | | | 78.6 | |
| LiN$_2$ | hexagonal | P6$_3$/mmc | a =2.631 c = 7.615 | | | 21.2 | white |
| LiN$_5$ | | P2 | | | | | |
| BeN$_4$ | triclinic | P1 | a=2.4062 b=3.5119 c=3.506 α=104.29° β=111.39° γ=96.71° | | | 85 GPa | |
| BeN$_4$ | monoclinic | P2$_1$/c | a=3.283 b=3.276 c=4.818 β=99.67° | | | 1 bar | 1D-chain |
| Na$_3$N$_8$ | tetragonal | I4$_1$/amd | a=4.9597 c=16.29 Z=4 | 400.7 | | | |
| NaN$_2$ | tetragonal | P4/mmm | a=3.001 c=4.101 Z=1 | 36.93 | | | |
| Mg$_2$N$_4$ | | | | | | | |
| MgN$_4$ | triclinic | P1 | a=3.58 b= 3.70 c=5.01 α=94.2° β=111.2° γ=71.6° | 58.7 | | @108 GPa >50 GPa | chains |
| K$_9$N$_{56}$ | orthorhombic | Ibam | a=5.2380 b=34.560 c=23.205 Z=8 | | | 61 GPa | |
| TiN$_2$ | tetragonal | I4/mcm | a=4.322 c=5.269 | | | | |
| VN$_2$ | tetragonal | I4/mcm | a=4.3015 c=4.9827 Z=4 | 92.195 | 5.6883 | 73.3 | bulk modulus 347 GPa |
| FeN$_2$ | orthorhombic | Pnnm | a=4.431 b=3.722 c=2.421 Z=2 | 39.93 | | 58.5 | |
| FeN$_4$ | triclinic | | a=2.5089 b=3.524 c=3.5409 105.08 110.26 92.03 Z=1 | 28.09 | | 106 | |
| CoN$_2$ | orthorhombic | Pnnm | | | | 31 GPa | bulk modulus 216 GPa |
| ZnN$_4$ | orthorhombic | Ibam | | | | 14-130 GPa | 1D-chain |
| YN$_6$ | | | | | | 100 GPa | N$_{18}$$^{9+}$ rings |
| Y$_2$N$_{11}$ | | | | | | 100 GPa | N-double helix |
| Y$_5$N$_{14}$ | tetragonal | P4/mbm | a=8.451 c=4.7316 Z=2 | 337.93 | 6.296 | 50 | |
| Nb$_2$N$_3$ | orthorhombic | Pnma | a=7.897 b=2.857 c=7.660 Z=4 | | 8.755 | 56 GPa | |
| NbN$_2$ | tetragonal | I4mm | a=2.8365 c=11.444 Z=4 | | 8.723 | 80 GPa | |
| NbN$_4$ | monoclinic | P2$_1$/n | a=4.4827 b=5.4543 c=5.439 β=101.47 Z=4 | | 7.59 | 105:100-120 GPa | |
| NbN$_5$ | orthorhombic | Fdd2 | a=11.833 b=13.870 c=3.6001 Z=16 | | 7.323 | 100-120 GPa | |
| RuN$_2$ | orthorhombic | Pnnm | | | | | |
| RhN$_2$ | orthorhombic | Pnnm | | | | | bulk modulus 235 GPa |
| PdN$_2$ | | Pa3 | | | | | |
| CsN$_5$ | | Pbca | | | | | penazolate |
| CsN$_5$ | triclinic | P1 | | | | | |
| LaN$_8$ | trigonal | R3 | | | | | N$_{18}$ rings |
| LaN$_8$ | tetragonal | P4/n | | | | | N$_8$ cage; high energy density |
| Ce$_2$N$_6$ | | C2/m | a=5.717 b=4.661 c=6.548 β=93.270 | 174.20 | | ambient | N$_4$ zigzags |
| CeN$_4$ | | I4$_1$/a | a=6.711 c=2.879 | | | | chains |
| CeN$_6$ | | R3m | a=5.890 c=4.108 | | | | hexazine |
| CeN$_{14}$ | hexagonal | P6mm | a =5.748 c =2.447 | | | | sheet |
| CeN$_{17}$ | hexagonal | P6mm | a=6.111 c=2.842 | | | | sheet |
| ReN$_2$ | monoclinic | P2$_1$/c | a=3.625 b=6.407 c=4.948 β=111.48° | | | 0 | hard; bulk modulus 330 GPa; N$_2$$^{4−}$ & N$^{3−}$ |
| OsN$_2$ | orthorhombic | Pnnm | | | | | bulk modulus 358 GPa |
| IrN$_2$ | monoclinic | P2$_1$/c | | | | | bulk modulus 428 GPa |
| PtN$_2$ | | Pa3 | | | | | bulk modulus 372 GPa |