Exploration of Archimedean Tessellations in Metal-Organic Frameworks

Exploration of Archimedean Tessellations in Metal-Organic Frameworks is the thesis authored by Hua Chen describing the research conducted under the supervision of Professor Kasper Steen Pedersen and has been submitted to the Department of Chemistry at the Technical University of Denmark.Among the classes of highly porous materials, metal-organic frameworks (MOFs) have excellent tunability, structural variety, and chemical and physical properties. MOFs are extended crystalline structures in which metal ions or clusters are connected by multitopic organic linkers. The diversity of metal ions and organic linkers allows an infinite number of combinations. MOFs have been used in several applications such as catalysis, gas sorption and storage, electronics, magnetoelectronics, photonics, and quantum technology. The identification of quasicrystals that exhibit long-range order but lack translational symmetry introduced a new class of materials and was a revolutionary breakthrough in crystallography. The combination of quasicrystals and metal–organic structures results in promising multifunctional systems with great potential for applications. Their construction principles have been extensively studied, and they are represented by numerous complex amorphous and crystalline phases. However, the quasicrystalline order in MOFs has been difficult to identify thus far. In this study, Archimedean tessellations were constructed in bulk MOFs by exploiting the inherent tendency of lanthanides to exhibit high coordination numbers. The prepared MOFs were characterized and determined to be quasi-crystalline approximants that exhibited excellent magnetic properties.The use of the plasticity of lanthanide (Ln) ions arising from the sufficient coordinative nature and the large ionic radii forms pentagonal bipyramidal nodes rarely found in the transition metal coordination chemistry. The self-assembly of linear {LnI2} nodes with ditopic organic spacers (4,4¢-bipyridine (bipy)) results in the formation of MOFs with layers exhibiting rare Archimedean tessellations that mimic the structural motifs of quasi-periodic 2D materials. The prepared MOFs (LnI2(bipy)_2.5) display intriguing magnetic properties and some of MOFs exhibit single molecule magnets behaviour.Furthermore, the tunability of a coordination network was explored, starting out from EuI2(pyz)_2.5 (pyz = pyrazine). The EuI2(pyz)_2.5 processes the elongated triangular tiling that can be considered as defect 6-fold nodes, which paves a way for establishing the real 6-fold nodes. The exchange of metal ions and ligands results in forming completely different structures. Furthermore, the magnetic properties of prepared MOFs have also been demonstrated.