New Luminescent Metal Organic Frameworks (MOFs) Incorporating Heterotopic Linkers as Chemical Sensors

Abstract

Metal‒organic frameworks, known as MOFs, are hybrid robust materials constructed from metal centers and organic linkers. The topicity of linkers used plays an important role in the predetermination of the structural attributes, properties and functionalities of MOFs. The earliest MOFs reported are composed of homotopic linkers, mainly attributed to their high symmetry and identical functional groups, which enables uniformity and homogeneity within the framework. On the other hand, the incorporation of heterotopic linkers (i.e. linkers containing more than one type of coordinating group) has long been an ongoing challenge. Apart from being non-symmetric, the uncertain coordination of all functional groups is the main obstacle faced in integrating heterotopic linkers in MOFs. However, it is more common that the different coordination groups incorporated tend to serve different limitations upon their incorporation within the MOFs structure. For instance, one coordinating unit acts to direct the geometry, structure and binding confinement; while other types of coordinating units act to complement functional assets of the framework. This thesis explores the integration of heterotopic linkers within two different and novel MOF structures having two different chelating groups; carboxylate and pyridine functional units and investigates its effects on its ability of luminescent sensing. The preparation, characterization methods and the MOF-guest interactions resulting in luminescent sensing are covered. The first structure integrates a rather simple heterotopic linker, 1,4-pyridinecarboxylic acid, known as isonicotinic acid (having one pyridine and one carboxylate functional units) and Cu(II) metal center to yield a 2-dimensional (2D) layered metal‒organic framework that is subsequently exfoliated into its complementary nanosheets and subjected cation and solvent sensing applications. The second structure assimilates a more complex heterotopic linker, 2,2':6',2''-terpyridine-4'-carboxylic acid, which includ