Structure, dynamics and reactivity of low-oxidation state iron complexes in solution studied by ab initio molecular dynamics simulations and advanced quantum chemistry calculations.

Third row (3d) metals, such as iron have become a candidate for a broad class of photocatalysts that have a large abundance on Earth and a low toxicity to humans and the environment. Unlike many commonly used photocatalysts that contain expensive precious metals, iron is cheap. Many important chemical processes such as the Haber-Bosch process or the Fenton’s reagent have employed an iron catalyst, however, in terms of metal complex photochemistry, this has been overshadowed by 4d and 5d metals with large affinities for unsaturated and saturated hydrocarbons. In an effort to understand the innate differences between a broad range of transition metals, electron configurations of the metal and its’ coordinating ligands are a natural starting point. The d-block orbitals can accommodate at most 10 electrons, while the splittings between the occupied and unoccupied orbitals are determined by the metal and the type of coordinating ligands. This often produces complicated electronic structures, with multiple low-lying spin states that can couple. To describe these electronic structures, robust quantum chemistry methods are required which can describe many geometric configurations of a metal complex in a variety of bonding conifgurations. Often these methods are coupled with dynamical simulation tools that can probe molecular processes in both the ground and excited electronic states in an isolated and bulk liquid environment. The present work aims to address many of these points by considering two different iron complexes: the brown-ring complex ([Fe(H2O)5(NO)]2+) and ironpentacarbonyl (Fe(CO)5). In the brown-ring complex, the ground state molecular dynamics (GSMD) have been simulated using Car-Parrinello molecular dynamics (CPMD) and the electronic properties have been presented. It is shown that a dynamical equilibrium between species have a unique spectroscopic signature, while the multireference character of the complex in the electronic ground state reveals a unique bondingconfiguration. In ironpentacarbonyl the excited state molecular dynamics (ESMD) have been performed to understand the mechanistic details that promote dissociation of one or more carbonyl ligands following excitation. In parallel to this study, the reactivity of the molecular fragments with the surrounding solvent molecules have been characterized