In this dissertation, investigations regarding magnetism within metal-organic frameworks (MOFs) based on calculations in the framework of density functional theory (DFT) were carried out.
On the one hand, the intrinsic magnetic properties within the MOF DUT-8(Ni) were studied (DUT -- Dresden University of Technology). This MOF is flexible, thus it can exist in two crystal structures named DUT-8(Ni)ppen and DUT-8(Ni)closed. A transition from one structure to the other can be achieved via e.g. gas adsorption, leading to a volume increase of approximately 260 %. The magnetic properties originate from spin-spin interactions between the unpaired electrons at the Ni centers. The magnetic coupling between the Ni ions was found to be low-spin (antiferromagnetic).
Considering that MOFs tend to have rather large unit cells (> 100 atoms), model systems (< 30 atoms) were generated. Such models can qualitatively as well as quantitatively describe the coupling inside the crystal structure while drastically reducing computational time. Furthermore, the model systems can be easily altered e.g. to introduce defects. The influence of these alterations on the magnetic coupling was studied. In addition, the metal centers have been exchanged by other 3d-metals to analyze the coupling constant with respect to different magnetic centers.
On the other hand, the magnetic shielding of Xe adsorbed into the MOFs UiO-66 and UiO-67 was investigated (UiO -- University of Oslo). Based on high-pressure nuclear magnetic resonance (NMR) measurements, which showed a decrease of the total chemical shift when going from the smaller MOF (UiO-66) to the larger one (UiO-67), a thorough theoretical analysis was carried out. For this purpose the ansatz of Ito and Fraissard, i.e. the chemical shift of Xe being a sum of different contributions, was employed. Accordingly, model systems which describe the influences of the MOFs and adjacent Xe atoms on the magnetic shielding were contructed. After equilibrating the Xe positions using molecular dynamics simulations, these model systems were taken to study the chemical shift of all Xe atoms individually. Thus, an analysis of the chemical shift inside each pore of the MOFs was carried out. This allows a description of different influences (Xe-surface, Xe-Xe) on the chemical shift, explaining the experimental behavior at an atomistic level.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:76320 |
| Date | 19 October 2021 |
| Creators | Trepte, Kai |
| Contributors | Seifert, Gotthard, Kortus, Jens, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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