Quantum Chemical Investigation of Functional Molecules

In this work, quantum chemical methods were applied to functional molecules. In the first part, spin crossover compounds were investigated, both experimentally and theoretically. A number of questions have arisen concerning the modulation of spin crossover properties and compounds when deposited on a surface which was adressed via synthesis and characterization of such a complex. It was found that the critical spin crossover temperature can change rather drastically between a bulk sample and a surface-adsorbed thin film which also enables light-driven switching of the latter. Furthermore, in light of these findings, it became clear that the ab initio prediction of spin crossover behaviour of a given compound would be desirable. Consequently, another study was carried out using wavefunction methods. Herein a local coupled cluster approximation was used to establish a protocol which was able to reliably reproduce canonical results for a set of test compounds. In the second part of this work, various systems of interest for the field of small molecule activation were investigated. The reactivity of a recently synthesized molybdenum dinitrogen complex in regard to nitrogen fixation was evaluated in terms of a free enthalpy profile including several possible catalytic pathways. The respective reactive species were analyzed utilizing several descriptors based on local molecular orbitals, bond orders and partial charges. Another Mo complex carrying CO ligands that has been synthesized and deposited on a gold surface via a platform approach was studied in terms of its geometric and electronic structure. This was conducted in a joint experimental and theoretical study employing vibrational and X-ray spectroscopy as well as an energy decom- position analysis to investigate the surface-molecule interactions. This resulted in a comprehensive picture of relevant properties. In the field of oxygen activation, copper(I) compounds were probed as it has been hypothesized that an equilibrium between the precursor, used in the synthesis of copper complexes, and a corresponding homoleptic complex carrying two ligands exists. To this end, a reaction energy profile was constructed and it was determinedthat such an equilibrium should, in fact, be possible. In the final project, a previously…