MECHANISM OF PHOTOSUBSTITUTION REACTIONS OF SQUARE-PLANAR PLATINUM(II) COMPLEXES .I. BROMODIETHYLENETRIAMINEPLATINUM(II)-NITRITE ION SYSTEM

The photochemical behavior of Pt(dien)Br+ in aqueous solutions containing various amounts of NO2− and Br− has been investigated. The excitation was performed with 313-nm radiations, corresponding to a ligand field band of the complex. In neutral solutions, the photosubstitution of Br− with NO2− was observed. The quantum yield for the photosubstitution reaction was in the range 0.007-0.04, and it increased with increasing [NO2−] and decreased with increasing [Br−]. When the irradiation was carried out in basic solution, only Pt(dien)OH + was obtained and its quantum yield of formation (φ 0.24) was independent of the amounts of N02″ and Br− present in the solution. The results obtained are interpreted on the basis of a photochemical Pt-Br heterolytic bond fission, leading to an ion-pair intermediate (presumably, Pt(dien)H2O2+ · Br− or Pt(dien)2+ · Br−). In neutral solutions, the intermediate can (i) react with NO2− to give the product, Pt(dien)NO2+; (ii) react with external Br− to give Pt-(dien)Br+; and (iii) undergo geminate recombination. The photochemical behavior in alkaline solution is accounted for on the basis of an efficient capture of the intermediate by the OH− ions. © 1969, American Chemical Society. All rights reserved.