Novel asymmetric heterobimetallic complexes of transition metals and the kinetics of oxygen binding to a cobalt(II) complex

A series of asymmetric heterobimetallic complexes of the type [LML′Sn]Cl and [LM′L′Sn]Cl2, where L = ethylene diamine, M = MnII, CoII, NiII and CuII, M′ = CrIII and FeIII and L′ = 1-tryptophan and 1-valine, have been synthesized and characterized by elemental analyses, u.v.–vis., i.r., e.p.r., n.m.r., cyclic voltammetry and conductivity measurements. The CoIII analogue of these complexes was characterized by two dimensional n.m.r. COSY data. The kinetics of oxygen binding with the complex [C15H23N4O2SnCo]Cl has also been studied. The kinetic data proves that CoII of a coordinated molecule participates in the rate-determining step of the dioxygen binding process. The plots of the pseudo-first-order rate kobsversus [O2] are linear passing through an intercept. The electrochemical behaviour of [C15H23N4O2SnCo]2+ and [C15H23N4O2SnCu]+ was monitored by cyclic voltammetry. Comparison of the electrochemical properties of [CoIIISnIV]2+ and [CuIISnIV]+ reveal that, in both the species, one electron transfer reaction takes place. For the [CoIIISnIV]2+ species E0 = 0.272 and −1.1 V and for the [CuIISnIV]+ species E0 = 0.078 and −0.300 V values were obtained, respectively.