<p>The mechanism of thermal solvation of the PtBr₆²⁻ complex in methanol and the photochemistry of PtBr₆²⁻ in methanol in the presence of free bromide ions were studied. It was established that thermal solvation of PtBr₆²⁻ in methanol is a two-stage process with an autocatalytic second stage, which gives rise to S-shaped kinetic curves displaying the changes in the UV absorption spectra of PtBr₆²⁻ solutions. A qualitative mechanism of the reaction is proposed. Steady-state photolysis and laser flash photolysis studies revealed that photoexcitation of PtBr₆²⁻ in methanol in the presence of free Br⁻ ions is accompanied by competing reactions, namely, photosolvation and two-electron photoreduction. The photoreduction is due to electron transfer from both solvent molecules and free bromide ions to the photoexcited complex to produce dihalide radical anions Br₂^•−. The reaction with the starting complex affording a pentavalent platinum intermediate contributes largely to the Br₂^•− decay. The values of the rate constant for this reaction in methanol and in water are discussed.</p>