A pulse radiolysis and flash photolysis study of the formation and characterization of platinum (III) amine complex ions

Abstract

An investigation into the formation and characterization of the transients arising from the reactions of hydroxyl radical with the complexes bis(ethylenediamine)platinum(II) perchlorate and chloride, chloro(diethylenetriamine)platinum(II) chloride and chloro(1,1,7,7-tetraethyldiethylenetriamine)platinum(II) chloride in aqueous media saturated with nitrous oxide has been carried out using the technique of pulse radiolysis. In general, the transients exhibit absorption bands with either a single, intense peak below 300 nm (ϵ ⪞ 400 m² mol⁻¹) or for the longer-lived species, two peaks of lesser intensity at about 350 and 500 nm. For the bis(ethylenediamine)-platinum(II) system, the transients are interrelated by acid-base reactions and in the presence of free chloride ion by substitution process. The disappearance of the longer-lived intermediate, which obeys second-order kinetics, does not lead to the formation of detectable amounts of ammonia (or free ethylenediamine). This feature in conjunction with other results indicates that the transients are not those arising from the degradation or loss of the co-ordinated amine ligand. Some of the intermediates exhibit reactivity towards either copper(II) perchlorate, an oxidant, or the reducing agent potassium ferrocyanide. The flash photolysis of trans-dichlorobis(ethylenediamine)platinum(IV) perchlorate has been used to generate and further characterize some of the transients encountered in the pulse radiolysis study. It is concluded that the intermediates are platinum(III) amine complex ions. For the Pt(III) species with absorption peaks below 300 nm, their structures are proposed to be distorted octahedra with substitutionally labile co-ordination sites. It is suggested that the products absorbing above 300 nm may be structurally different from those absorbing below 300 nm.