From structure to application: studies on adenine-, pyrene- and lanthanide-based metal-organic frameworks

Metal-organic frameworks (MOFs) are coordination polymer materials in which inorganic metal ions or clusters are linked with multitopic organic ligands by means of coordination bonds. Their structural versatility allows for design of materials based on pre-formed building blocks, whereas their crystallinity enables the study of their underlying structures on the atomic level. The bottom-up approach of materials discovery involves first the study of the structure of the newly synthesised material followed by a detailed characterisation, from which a potential application is inferred.

This thesis presents the synthesis, structural determination and full characterisation of 10 novel MOFs constructed from ligands including adenine and pyrene-based H4TBAPy as well as a lanthanide-based MOF. Based on their crystal structures, a variety of applications has been postulated for these materials, and the comparison with the materials already known in the literature has been undertaken.

In SION-10, the presence of active Cu(II) centres and non-coordinated Cu(II)-adenine complexes in the structural voids of the material was found to be key factors enabling the capture of ammonia with this material. Adenine-based SION-31-35 served as a platform for investigation of N-protonation sites due to the different binding modes displayed by adenine in their structures. Bi-porous nature of the pyrene-based SION-8 was used for as a proof of concept for CO2/CH4 separation of tuneable selectivity and for irreversible capture of iodine. In SION-7, the mutual orientation of the pyrene-based ligands and the pore content were shown to influence the fluorescence emission of the material, and to be finely tuneable by temperature changes. The lanthanide-based SION-2 was found to exhibit a strong negative thermal expansion effect, which arises from the coordination flexibility of lanthanides, the geometric features of the material, and the presence of guest molecules.

The modified bottom-up approach of materials discovery is an efficient method of accessing novel materials for targeted applications.