Recent Developments in Organic Radical Inclusion in MOFs and Radical MOFs

Inclusion of organic radicals in porous materials offers an opportunity to tailor properties that include stability of radicals, conductivity, sensing, and catalysis. Similarly, radical metal-organic frameworks (MOFs) are synthesised to enhance or create such properties. This review provides details on methods of organic radical inclusion in MOFs, synthesis of radical MOFs, and potential properties.

Organic radicals are attractive materials due to their structures which contain unpaired electrons susceptible to charge transfer upon excitation. They possess potential properties such as optical properties, magnetism, and electrical conductivity. However, they are usually unstable impeding their further advancement and application. Organic radicals can serve as guest molecules in porous solids specifically metal–organic frameworks (MOFs) thereby gaining stability. MOFs are of interest due to their potential properties including large surface area and high adsorption capacity. Apart from their incorporation to form organic radical inclusion MOF hybrids, organic radicals can act as ligands in MOFs to yield radical MOFs. These hybrids and radical MOFs often exhibit enhanced properties such as improved catalytic, magnetic, optical, and sensing properties which make them promising for industrial applications. Herein, organic radical inclusion in MOFs and radical MOFs are reviewed. A brief background on organic radicals is presented. Different methods of integrating organic radicals (guests) in channels of MOFs (hosts) and the resulting changes in the physicochemical properties are documented. Furthermore, the use of organic radicals as ligands in the synthesis of radical MOFs is discussed as an alternative to organic radical–MOF inclusion compounds, and the ensuing physicochemical properties are highlighted.

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