Dissertation: "Structural, electronic and reactive properties of pentapyridyl - base-metal complexes: Relevance for water oxidation catalysis"
- Location: Zoom Siegbahnsalen
- Doctoral student: Manuel Boniolo
- About the dissertation
- Organiser: Department of Chemistry - Ångström Laboratory
- Contact person: Johannes Messinger
- Phone: 018-471 3671
Manuel Boniolo defends his PhD thesis entitled "Structural, electronic and reactive properties of pentapyridyl - base-metal complexes: Relevance for water oxidation analysis" within the subject of chemistry with specialization in molecular biomimetics.
Opponent: Prof. Antoni Llobet, Institute of Chemical Research of Catalonia (ICIQ), Tarragona, Spain
Main supervisor: Prof. Johannes Messinger, Department of Chemistry - Ångström, Uppsala University
Assistant supervisors: Prof. Sascha Ott, Synthetic Molecular Chemistry, Department of Chemistry - Ångström, Uppsala University, and Prof. Thomas Wågberg, Department of Physics, Umeå University
Due to the Corona restrictions, it will be possible to follow the dissertation on Zoom via the link: https://uu-se.zoom.us/j/64388410437.
The rationalization of chemical-physical proprieties of transition metal complexes is fundamental in order to understand and tune their reactivity. In this thesis, a systematic investigation of the geometrical and electronic properties of [M(Py5OH)Cl]+ complexes (M= Mn, Fe, Co, Ni) has been performed, and their ability to act as molecular water oxidation catalysts has been probed. Through this scientific journey, new insights into their chemical and physical properties have been revealed. The spin crossover behavior of the ferrous chloride complex ([Fe(Py5OH)Cl]PF6) is the first example of a molecular Fe(II) complex coordinated to a weak-field ligand that can be thermodynamically stable in a low-spin electron configuration (Chapter 3). The spin state also dictates the electrochemical proprieties of the one-electron oxidized state of all the metal complexes investigated in our study (Chapter 4). The atypical rhombicity of the manganese complex ([Mn(Py5OH)Cl]PF6) gives an unusual anisotropic EPR signal for a Mn(II, S = 5/2) complex. This is compared with the analog [Mn(Py5OMe)Cl]PF6 complex providing, in combination with DFT calculations, insight into how the magnetic parameters (i.e., zero field splitting) are affected by small structural changes (Chapter 5). Finally, I investigated the role of water as substrate for water oxidation catalysis with the [M(Py5OH)Cl]+ complexes. The addition of small amounts of water into a non-aqueous medium allowed trapping possible water-bound intermediates for the Fe complex in the M(III) oxidation state but not for the other complexes. Nevertheless, all Py5OH-metal complexes are not particularly active catalysts with a maximum turnover number (TON) of 2. By introducing two methoxy functional groups, we obtained [Fe(Py5OMe)Cl]+ that turns out to facilitate water oxidation catalysis with a TON = 133 in a light-driven experiment. Further electrochemical experiments and post-catalytic solution analysis reveals that the oxygen evolution is generated by iron oxo/hydroxo species formed from the degradation of the methoxy-substituted Fe complex. This study highlights the difficulty of obtaining a stable base metal molecular catalyst and the importance of conducting a multi-technique analysis to attest firmly the nature of the catalysis (Chapter 6).