Photochemistry of the PtCl 62− complex in methanol solution

Abstract

In the laser flash photolysis of PtCl 6 2− in methanol, a non-linear dependence of the yields of the trivalent platinum intermediates PtCl 6 3− and PtCl 5 2− on laser pulse intensity is observed. The non-linearity is due to the absorption of photons by PtCl 6 3− which is a primary product resulting from the electron transfer from a methanol molecule to excited PtCl 6 2−. Photodissociation of PtCl 6 3− yields PtCl 5 2−. However, PtCl 6 3− in the ground state also dissociates into PtCl 5 2− and Cl −. This monomolecular process proceeds with an activation energy of 29.7 kJ mol −1 and a rate constant of 1.05 × 10 6 s −1 at 300 K. The parameters of the reverse reaction between Cl − and PtCl 5 2− which yields PtCl 6 3− have also been measured (activation energy, −9.6 kJ mol −1; rate constant at 300 K, 7.6 × 10 6 M −1 s −1). When free Cl − is present in methanol at a concentration of more than 0.1 – 0.2 M, electron transfer from Cl − to excited PtCl 6 2− is also possible. The chlorine atom formed reacts with Cl − yielding the radical ion Cl 2 − which is detected by an intense absorption band with a maximum at 340 nm.