The electroreduction of azides bound to nickel(II) ions in weak acidic media

Azide ions undergo reduction at the mercury electrode in slightly acidified media if they are coordinated to Ni(II) ions. Under such conditions, the electroreduction of Ni(II) to nickel amalgam is followed, at more negative potentials, by the parallel reduction of the ligand. The macro-scale electrolysis of slightly acidified solutions of $\mathrm{Ni}(\mathrm{II})''–''{\mathrm{N}}_3^{-}$ complexes showed the formation of ammonia and the evolution of bubbles of colorless gas. The electrode mechanism involves the direct electroreduction of ${\mathrm{N}}_3^{-}$ ions in the coordinated state according to the reaction scheme: ${\mathrm{N}}_3^{-}+4{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\to {\mathrm{N}}_2+{\mathrm{NH}}_4^{+}$ as the suggested main reaction pathway, accompanied by a side reduction of ${\mathrm{N}}_3^{-}$ by nickel amalgam. In terms of this mechanism, the average coordination number of the reacting $\mathrm{Ni}(\mathrm{II})''–''{\mathrm{N}}_3^{-}$ complexes could be deduced. A molecular mechanism of the electroreduction of the azide ion bound to Ni(II) central ion was suggested.