Synthesis and real structure effects in Zr-based metal–organic frameworks

Koschnick, Charlotte (2022): Synthesis and real structure effects in Zr-based metal–organic frameworks. Dissertation, LMU München: Fakultät für Chemie und Pharmazie

Abstract

After more than two decades of research in the field of metal–organic frameworks (MOFs), a plethora of structures has been reported and used for a variety of applications including catalysis, gas adsorption, and drug delivery. Zr-based MOFs have emerged as pioneering materials due to their outstanding stability and structural flexibility. Although new Zr-based MOFs are published frequently, systematic investigations on disorder and vacancies in the structures, which are known to affect the materials’ properties, remain sparse. In addition, synthetic reports are often irreproducible, leading to phase mixtures of two or more MOFs limiting their utility in targeted applications. This thesis investigates the structural complexity of Zr-based MOFs, in particular cluster disorder and vacancies, and explores the link between synthesis parameters and product outcome. Combination of Zr-oxo clusters with the chromophore tetrakis(4-carboxyphenyl)porphyrin gives rise to a series of porphyrinic MOFs with interesting (opto)electronic properties. Chapter 2 explores the structures of the cubic representatives PCN-221, MOF-525, and PCN-224. Based on a comprehensive synthetic and structural analysis spanning the local- and long-range, it was found that PCN-221 consists of octahedral Zr6O4(OH)4 clusters tilted in four directions, rather than cubic Zr8O6 clusters as previously reported in literature. A new structure model—disordered PCN-224 (dPCN-224)—was established to understand cubic porphyrinic Zr-based MOFs with varying degrees of orientational cluster disorder, linker vacancies, and cluster–linker coordination. In a further step, Chapter 3 evaluates the complexities of synthesising porphyrinic Zr-based MOFs, specifically dPCN-224. A detailed step-by-step formation pathway of dPCN-224 was characterized, revealing that the MOF formed via an intermediate. Importantly, it was shown that the Zr source and water content in the reaction influenced the formation of the inorganic building unit and with this the resultant product. Additionally, Chapter 4 explores the structural complexity of Zr-based MOFs with methane-tetrakis(p-biphenylcarboxylate) (MTBC) linkers. Two new MTBC-based structures are presented, namely c-(4,12)MTBC-Zr6 and t-(4,12)MTBC-Zr6, that show unexpectedly high structural versatility. The 12-fold cluster coordination found in both structures is enabled by a combination of cluster disorder and linker flexibility. Importantly, Hf analogues were also obtained for both structures revealing that the structural flexibility is not limited to Zr–MTBC compounds.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: Zr MOFs, Porphyrin MOFs, MTBC MOFs
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 540 Chemie
• Fakultäten: Fakultät für Chemie und Pharmazie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 14. November 2022
• 1. Bericht­erstatter:in: Lotsch, Bettina