Reactions of pentacyanonitrosylferrate(2-), ((NC),FeN02", nitroprusside) with hydroxylamine and azide were examined.With azide at pH 6, N2 and N,0 are produced according to the equation (NC)sFeN*Q2' + *NNN" + H20 = (NC)S-FeH203" + N2 + *NN*0. The rate law for the first step, the formation of a nitrosyl-azide adduct, I, is assumed to be d[I] /df = fcla[(NC)sFeN02'] [N3~], with ki& = 0.2 AT1 sec"1 at pH 6, T= 23°. This adduct decomposes to give (NC)S-FeH203" (Xmax 455 nm, e 460 M~l cm"1), N2, and N20; and the rate law is assumed to be -d[I]/df = Ar^fl]; k^i s approximately 0.2 sec"1 at pH 6, 7= 23°. The complex (NC)sFeH203' dimerizes to (NC)10Fe,6" (Xmax 395 nm, e 940M"1 cm"1). In excess azide the dimer reacts to form (NC)sFeN34~(Xmax 440 nm, e 1400 M'1 cm"1); the rate law is d[(NC)5-FeN34"]/df = fc2[(NC)10Fe26"][N3"], with kt = 1.0 (±0.1) X 102 M"1 sec"1 at pH 6, 7=23°. £°for the couple (NC)S-FeN33" + e" = (NC)sFeN34" is-0.3 (±0.1) V and (NC)5FeN34" is oxidized by 02 according to the equation d[(NC)s-FeN33']/dí = fc3[(NC)5FeN34"][02], with k3 = 3.0 (±0.7) X 102 M~' sec"1 at pH 6,7=23°. Hydroxylamine reacts with (NC)jFeNO2" according to the equation (NC)5FeN02" + *NH2 *OH + OH" = (NC)sFeH203" + N*N*0 + H20. An intermediate, 3 (Xmax 445 nm, e 700 M'1 cm"1), is formed, the rate law being d[J]/df = k4a[(NC)5FeN02"][NH20H][0H"], with &4a = 4.5 X 10s M~2 sec"1 at 25°a nd£a = 9.5 ± 1.0 kcal/mol. The possibility exists that J is (NC)5FeN203". Subsequent reactions occurred which were not quantitatively examined. It is apparent from these studies that the stability of pentacyanoferrate(II) complexes toward oxygen oxidation is strongly dependent on the rr-accepting ability of the sixth ligand.
