According to X-ray crystallography the  linkage is linear in typical diazonium salts. The  bond distance in benzenediazonium tetrafluoroborate is 1.083(3) Å, which is almost identical to that for dinitrogen molecule (N≡N).
The linear free energy constants σ and σ indicate that the diazonium group is strongly electron-withdrawing. Thus, the diazonio-substituted phenols and benzoic acids have greatly reduced pK values compared to their unsubstituted counterparts. The pK of phenolic proton of 4-hydroxybenzenediazonium is 3.4, versus 9.9 for phenol itself. In other words, the diazonium group lowers the pK (enhances the acidity) by a million-fold.
The stability of arenediazonium salts is highly sensitive to the counterion. Phenyldiazonium chloride is dangerously explosive, but benzenediazonium tetrafluoroborate is easily handled on the bench.
S1 and S2 reactions do not occur.
Arenediazonium salts are versatile reagents as described in the next sections After electrophilic aromatic substitution, diazonium chemistry is the most frequently applied strategy to prepare aromatic compounds.