REACTIONS OF [NI(1,4,7-TRIAZACYCLONONANE)2]3+/2+ WITH THE COMPONENTS OF NITROUS-ACID

The reactions of [Ni(tacn)2]3+ with some of the components of nitrous acid have been studied in aqueous solution at 25-degrees-C. NO2- reacts to form [Ni(tacn)2]2+ and NO3-, and the rate law is -d[Ni(tacn)2(3+)]/dt = k[Ni(tacn)2(3+)][N(III)]/(1 + [H+]/K(a)) with k = 212 +/- 7 M-1 s-1 and K(a) = (9.6 +/- 1.1) x 10(-4) M at mu = 0.1 M (LiClO4). Electron transfer from NO2- to [Ni(tacn)2]3+ is proposed as the rate-limiting step. In 0.79 mM NO, [Ni(tacn)2]3+ reacts with the rate law -d[Ni(tacn)2(3+)]/dt = k'[Ni(tacn)2(3+)] + k"[Ni(tacn)2(3+)]/[H+] where k' = (1.02 +/- 0.06) x 10(-3) s-1 and k" = (1.36 +/- 0.07) x 10(-4) M s-1 at mu = 1.0 M (LiClO4). The k" pathway leads to destruction of the complex, presumably through nitrosation of the N-deprotonated conjugate base form of the Ni(III) reactant. The k' pathway is interpreted as an outer-sphere electron-transfer reaction between NO and [Ni(tacn)2]3+.