Engineering flexible metal-organic frameworks from methylene-hinged ligands

This thesis focuses on the synthesis of functional materials composed of ligands that possess a methylene hinge – a flexible link between two coordinating groups – and the capacity to form a six-membered chelate ring with transition metals that moderates structural flexibility. A significant portion of this work characterises and explores the properties of a class of functional materials called metal-organic frameworks (MOFs). By utilising methylene-hinged ligands, MOFs are designed that contain intrinsic flexibility and consequently interesting guest exchange and gas adsorption properties. The first methylene-hinged ligand described, di-2-pyrazinylmethane, exhibited an exceptionally rich coordination chemistry with silver(I). Appropriate conditions led to the crystallisation of three isostructural 3-D silver(I) MOFs with large 1-D channels. Although these materials lacked permanent porosity, they possessed the ability to undergo guest-induced structural contraction and expansion. This remarkable solid-state behaviour was related to the chemistry of the guest. The theme of structural flexibility is continued in subsequent chapters which describe the structural flexibility and gas adsorption properties of several MOF materials composed of Cu(II), Co(II), Ni(II), or Mn(II) and the ligand bis(4-(4-carboxyphenyl)-1H-pyrazolyl)methane or bis(4-(4-carboxyphenyl)-3,5-dimethyl-1H-pyrazolyl)methane. Some of the work reported in chapter 3 that deserves particular attention is the exceptional CO₂/N₂ selectivity of a Cu(II) MOF. This material undergoes post-synthetic structural contraction to achieve pore dimensions capable of discriminating between CO₂ and N₂ based on their respective kinetic diameters. Another noteworthy material is described in chapter 4; a flexible Mn(II) MOF capable of quantitative post-synthetic metal binding with preservation of single-crystallinity. The framework flexibility of this material allowed elucidation of the primary coordination sphere of the grafted metal ion and subsequent solid-state transformations by X-ray crystallography. A large portion of this thesis demonstrates and emphasises the positive impact of structural flexibility in MOFs as functional host materials. Chapters 5 and 6 describe methylene-hinged compounds from the viewpoint of synthetic precursors to more complex ligands that contain a fused pyrazino[2,3-b]indolizine or indolizino[2,3-b]quinoxaline core. The synthesis, metal complexes, and corresponding solid-state structures of a series of these ligands are described.

Author dc:creator

• Bloch, Witold Marek

Advisor dc:contributor.advisor

• Sumby, Christopher James

• metal-organic frameworks

Handle dc:identifier.uri

http://hdl.handle.net/2440/98710

OAI identifier oai:identifier

oai:digital.library.adelaide.edu.au:2440/98710