Dealing with Complexity in Open-Shell Transition Metal Chemistry from a Theoretical Perspective: Reaction Pathways, Bonding, Spectroscopy, And Magnetic Properties

This chapter illustrate the challenges that are met in theoretical transition metal chemistry: (1) reactivity of high-valent iron-oxo sites and the challenge of multiple spin-state channels; (2) The treatment of magnetic spectroscopic observables in the case of (near) orbital degeneracy; (3) The experimentally validated description of transition metal complexes with coordinated ligand radicals; (4) The calculation of the magnetic properties of oligonuclear transition metal clusters with applications to Photosystem II. The subjects treated in the chapter are related to the fact that open-shell transition metals display a high degree of electronic complexity. This shows up in their reaction pathway that will frequently show multistate reactivity. Likewise, the magnetic and electronic properties of open-shell transition metals can be very complicated, as the case of Jahn Teller systems, and special techniques need to be employed to successfully model them. The intricate bonding situations that are created by exchange coupling (in essence, nothing but a very weak chemical bond) in metal radical systems and oligonuclear metal clusters are another area that is highly challenging to theory.