Reduction Process of Pt(IV) Complexes With Axial Acetato Ligands by Ascorbic Acid; Comparison of Experimental and Computational Tools.

In the present work, the reduction mechanism of several Pt(IV) complexes bearing two axial acetato ligands by ascorbic acid (AA) was investigated. The computational approach is based on the grand-canonical formulation of the Gibbs-Alberty free energy, in which pH serves as an internal thermodynamic variable instead of the amount of substance. This framework enables the evaluation of pH-dependent rate constants, which is essential because the neutral form of AA reacts relatively slowly with Pt(IV) complexes. The rate constants were estimated using two DFT functionals, B3LYP and M06-2X, in combination with the LANL2DZ basis set. To improve the accuracy, single-point energy corrections employing extended basis sets, an improved PCM solvation model with cavity scaling based on NBO partial charges, and the Wertz entropy correction accounting for the transition from the gas phase to solution were also applied. The proposed computational approach provides good qualitative agreement with the experimentally determined reduction rates for all investigated Pt(IV) complexes except one, which most likely undergoes reduction through a different reaction mechanism.