Formation and characterization of platinum(III)-ethylenediamine complex ions using pulse radiolysis

Abstract

Pulse radiolysis experiments using conductivity, polarographic and uv-visible absorption detection techniques have been carried out on the reaction of hydroxyl radical with bis(ethylenediamine)platinum(II)perchlorate in aqueous media. This reaction is shown to proceed by OH addition to the platinum center to yield a nascent product where the metal is in a formal oxidation state of III. The subsequent behavior of this Pt(III) transient generates three additional transients, whose formations are dependent upon the pH and presence of free chloride ion. A mechanism is proposed whereby these transients are interrelated through acid-base, chloride substitution, and water elimination processes. Evidence is presented to support the classification of the Pt(III) species into two groups having the compositions of Pt(en)/sub 2/(X)/sup n+/ (X = OH, H/sub 2/O, Cl; n = 2,3) and Pt(en)(en-H)/sup 2 +/ (en-H = /sup -/NHCH/sub 2/CH/sub 2/NH/sub 2/). For the former group, the respective wavelength maxima and molar absorption coefficients are 270 nm, ca. 4500 M/sup -1/ cm/sup -1/ (X = OH), < 250 nm (X = H/sub 2/O), and 260 nm, 8000 M/sup -1/ cm/sup -1/ (X = Cl). For Pt(en)(en-H)/sup 2 +/, two absorption bands are found with peaks at 340 nm (2900 M/sup -1/ cm/sup -1/) and 480more » nm (1500 M/sup -1/ cm/sup -1/). This latter species is also the major product of the reaction of the hydrated electron and trans-di-hydroxobis(ethylenediamine) platinum(IV) perchlorate which was investigated by absorption and conductivity techniques. The possible structures of these intermediates are discussed.« less