# Analogies of azide?

Azide is a fairly common ion, but why aren’t there similar versions such as $\ce{P3-}$ or $\ce{B3+}$? Do they exist, is there something wrong with these ions as to make them more likely to just break apart rather than for ionic compounds.

Compare the covalent radii of $\ce{N}$ ($75\,\mathrm{pm}$) and $\ce{P}$ ($106\,\mathrm{pm}$).
Phosphorus is a bit on the chubby side. Larger atom-to-atom distance means less overlap of p-orbitals in multiple bonds: $\ce{P=P}$ and $\ce{P#P}$ bonds are much weaker than similar bonds between nitrogen atoms.