Disputation: "Structural, electronic and reactive properties of pentapyridyl - base-metal complexes: Relevance for water oxidation catalysis"

  • Datum:
  • Plats: Zoom Siegbahnsalen, Lägerhyddsvägen 2
  • Doktorand: Manuel Boniolo
  • Om avhandlingen
  • Arrangör: Institutionen för kemi - Ångström
  • Kontaktperson: Johannes Messinger
  • Telefon: 018-471 3671
  • Disputation

Manuel Boniolo försvarar sin doktorsavhandling med titeln "Structural, electronic and reactive properties of pentapyridyl - base-metal complexes: Relevance for water oxidation analysis" inom ämnet kemi med inriktning mot molekylär biomimetik.

Opponent: Prof. Antoni Llobet, Institute of Chemical Research of Catalonia (ICIQ), Tarragona, Spain

Handledare: Prof. Johannes Messinger, Institutionen för kemi - Ångström, Molekylär biomimetik, Uppsala universitet

Bitr. handledare: Prof. Sascha Ott, Syntetisk molekylär kemi, Institutionen för kemi - Ångström, Uppsala universtet, och Prof. Thomas Wågberg, Institutionen för fysik, Umeå universitet 

Pga Corona-restriktionerna så kommer det kunna gå att följa disputationen på Zoom via länken: https://uu-se.zoom.us/j/64388410437.

Länk till doktorsavhandlingen i DiVA.

Abstract

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).

 

Disputation: