FORMATION OF PT(III) COMPLEXES IN IRRADIATED POTASSIUM TETRANITROPLATINATE(II) - A SINGLE-CRYSTAL ESR STUDY

X-irradiation of single crystals of K2[Pt(NO2)4] and of K2[Pt(NO2)4].2 H2O leads to the formation of Pt(III) complexes which have been studie d by EPR at 77 K. The crystal structure of the hydrated compound has b een determined in order -to interpret the orientation of the g and Pt- 195 hyperfine tensors and to reassign the powder spectrum previously a ttributed to this compound. The nature of the trapped species is shown to be dependent upon the presence of water molecules: one of the two Pt(III) complexes formed in the hydrated crystal probably results from oxidation of the original molecule by the radiogenic OH. radical wher eas, for the second species, the water molecule seems only to particip ate in the stabilization of the Pt(III) complex. For the anhydrous com pound this stabilizing effect is probably assured by a distant NO2 gro up.