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A DFT Investigation of Transition Metal Redox Reactions: a conceptual DFT and ab initio Molecular Dynamics Approach

Friday, 17 September, 2010 - 11:00
Campus: Brussels Humanities, Sciences & Engineering campus
Jan Moens
phd defence

The central theme of this thesis is the study of electron transfer reactions of solvated transition metal ions through density functional theory (DFT). In the field of computational chemistry, DFT plays a vital role to provide not only the computational power to tackle chemical problems but also to define precise chemical concepts in its conceptual DFT branch. Over the past years, these concepts have found widespread use for the interpretation of mostly organic reactions. In this thesis we assess for the first time the thermodynamics of electron transfer reactions based on these chemical concepts. In the first part of this thesis, the main focus is on the electrophilicity descriptor. The power of this index to resolve standard redox potentials is discussed for one electron reduction half reactions of first row transition metal ions in aqueous solution.

In a second conceptual DFT approach, the standard redox potential is written in terms of the chemical potentials and hardnesses of oxidized and reduced species by invoking a grand canonical ensemble approach.  Computational work is compared to experimental standard redox potentials of a large set of organic and inorganic systems embedded in different kind of solvents.

The properties observed in a series of transition metal complexes can vary widely depending on the nature of the coordinating ligand. In this thesis special attention goes to the spectrochemical series, the nephelauxetic series and the electrochemical series. The first two series are described within a conceptual Spin-Polarized DFT formalism through the spin-philicity descriptor and the spin Fukui function. A computed electrochemical series is constructed based on an electrochemical parameter that is derived from the slopes of the linear curves of the adiabatic energy differences for the oxidation half reaction of [M(CO)_n L_(6-n)] complexes with respect to the CO substitution number n.

In the last part of this thesis, we combine energy resolved photoelectron measurements and density functional molecular dynamics simulations to extract information about the electronic properties of the aqueous Mn^(2+/3+) redox pair. After including some correction terms in the computational results, the computed values are shown to be in good agreement with the experimental electron binding energy, redox potential and reorganization free energy.