The base hydrolysis kinetics and crystal structures of some neutral mer-triaminetrinitrocobalt(III) complexes

The release of nitro groups from neutral mer-triamine-trinitrocobalt(III) c omplexes [triamine = 2,2-tri (dien) (1), 2,3-tri (2), 3,3-tri (dpt) (3), (N H,)(en) (4), (NH3)(tn) (5)], in the presence of greater than or equal to 10 fold excess hydroxide ion, proceeds in two distinct, pseudo-first-order, s teps. For both steps, plots of k(obs) vs [OH-] are linear in the range 0.02 5 less than or equal to [OH-] less than or equal to 1.0 M with zero interce pt. For the tridentate triamines, the first step corresponds to the formati on of mer-[Co(OH)(NO2)(2)(triamine)] and the final product is mer-[Co (OH)3 (triamine)]. As with mer-[Co(NO2)(3)(NH3)(3)], the ammine complexes, 4 and 5, form precipitates at long reaction times. The classic base hydrolysis be haviour of those neutral complexes suggests that ion-pairing is not mechani stically important and the data can be interpreted in terms of the conventi onal S(N)1CB (DCB) mechanism. The crystal structures of 2, 3, 5 and [Co(NO2 )(3)(Medpt)] (6) have also been determined, confirming the mer- configurati on.