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 [LMLSn]Cl and [LMLSn]Cl₂, where L = ethylene diamine, M = Mn^II, Co^II, Ni^II and Cu^II, M = Cr^III and Fe^III 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 Co^III 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 Co^II of a coordinated molecule participates in the rate-determining step of the dioxygen binding process. The plots of the pseudo-first-order rate k_obsversus [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 [Co^IIISn^IV]²⁺ and [Cu^IISn^IV]⁺ reveal that, in both the species, one electron transfer reaction takes place. For the [Co^IIISn^IV]²⁺ species E⁰ = 0.272 and –1.1 V and for the [Cu^IISn^IV]⁺ species E⁰ = 0.078 and –0.300 V values were obtained, respectively.