Top-Down Approaches for the De-Reticulation and Synthesis of Metal-Organic Frameworks

Abstract

The present PhD Thesis has been devoted to the study, understanding and implementation of novel top-down approaches for the rational design of reticular materials built with less-symmetric molecular building blocks (MBBs). Two strategies are proposed based on the de-reticulation of nets to accomplish this objective. The first approach, net-clipping, is based on the theoretical clipping of more-symmetric MBBs for the topological prediction of nets constructed with less-symmetric MBBs. The second approach, Clip-off Chemistry, is based on the programmed disassembly of reticular materials by bond cleavage at specific, controlled positions. Chapter 1 encompasses a general introduction and the development of the reticular chemistry field, from their discoveries and conception to their rationalization and classification. Additionally, we focus on the most relevant synthetic and post-synthetic methodologies used for designing reticular materials to contextualize the reader to the significance of the presented work in this Thesis. Chapter 2 introduces the general and specific objectives of this Thesis. In Chapter 3, we review the state of the art of the effect of desymmetrization of organic MBBs on the assembly of Metal-Organic Frameworks (MOFs) based on high-connected Zr- and rare-earth (RE)-clusters. We study the most important desymmetrizations performed in literature and how these affects to the connectivity and geometry of the cluster, and therefore, to the net. Moreover, less-symmetric MBBs are designed for the synthesis of novel MOFs to understand the different chemical behaviour of similar high-connected inorganic MBBs. Chapter 4 describes the first top-down approach, net-clipping, based on the de-reticulation of MOFs and edge-transitive nets by clipping MBBs or nodes of higher connectivity and symmetry by half. We select the clippable MBBs with 4-connected (4-c) square/rectangular, 4-c tetrahedral, 6-c hexagonal, 8-c cubic, and 12-c hexagonal prismatic linkers to decrease its symmetry into less-regular MBBs. By applying net-clipping to all the nets constructed with nodes with these connectivities and shapes, 141 derived and 56 clipped nets are anticipated, being 39 of them described for the first time. We validate our strategy with the synthesis of 6 novel MOFs constructed with less-symmetric MBBs and several literature examples that confirm our predictions. Chapter 5 describes a new synthetic methodology, Clip-off Chemistry, based on the de-reticulation of MOFs via bond breaking for the obtention of novel molecules or materials. We validate our strategy with the synthesis of two topologically different tridimensional (3D) MOFs (Zr-pcu-MOF and Sc-pcu-MOF) from other two different 3D MOFs as precursors (Zr-scu-MOF and Sc-soc-MOF, respectively). Using the ozonolysis reaction and double bonds as our cleavable reaction/groups, respectively, we demonstrate that this transformation can be performed quantitively, selectively, and periodically, occurring in a single-crystal-to-single-crystal fashion.

Date of Award	23 Feb 2024
Original language	English
Supervisor	Daniel Maspoch Comamala (Director) & Inhar Imaz Gabilondo (Director)