The Jahn-Teller effect in MOF’s: breaking symmetry for increased stability
The Jahn-Teller effect in MOF’s: breaking symmetry for increased stabilityPromotor(en): S. Cottenier, D.E.P. Vanpoucke /15_NANO16 / Nanoporous materials
Molecules and solids are very often represented using ball-and-stick models. In these models, atomic positions are indicated with spheres, while the bonds between the atoms, formed by pairs of valence electrons, are indicated with the sticks. However, the valence electrons are not the only electrons present in the space between the atomic nuclei which are of importance for the geometric structure of a system.
In 1937, Hermann Arthur Jahn and Edward Teller showed that for molecules a non-linear symmetry and a degeneration of the electronic ground state are incompatible. Using group-theory they showed that lifting the electronic degeneracy in these molecules results in a lowering of the symmetry of the system and an increase in the stability of the ground state. Since the removal of the degeneracy goes hand in hand with a distortion of the original symmetry this effect is known also as a “Jahn-Teller distortion”.
Jahn-teller distortions are often observed for transition metals in an octahedral coordination. In MIL-53 like metal organic frameworks (MOFs) the metal oxide clusters show a metal site in such an octahedral coordination, making this a suitable environment for the observation of Jahn-Teller distortions. For other MOFs Jahn-Teller distortions have already been observed, and theoretically studied. In those studies it was even shown that the Jahn-Teller distortion can be a driving force for 1 dimensional magnetic behavior. In MIL-53 like MOFs Jahn-Teller distortions have not yet been investigated.
In this topic, suitable candidate transition metals will be selected for different MOF topologies (MIL-53/MIL47). The student will investigate the Jahn-Teller effect using state of the art solid state simulation methods and relate this to the properties of the selected transition metal. Also the influence of the Jahn-Teller distortion on the electronic and structural properties of the MOF itself will be investigated, with specific focus on the magnetic properties of the MOF.
Interested students will be trained in the use of the required quantum mechanical codes and tools necessary for this topic.
- Study programmeMaster of Science in Engineering Physics [EMPHYS], Master of Science in Chemistry [CMCHEM], Master of Science in Physics and Astronomy [CMFYST]ClustersFor Engineering Physics students, this thesis is closely related to the cluster(s) Modelling, Fundamentals, Nano, Materials