Redox-active metal-organic macrocycles and nanocages: From functionality to function

Metal-organic macrocycles and nanocages have attracted great interest for their fascinating structures as well as for their functional behaviors, including host-guest chemistry, catalytic activity, and stimuli-responsive structural rearrangements. Interest in redox-active versions of these discrete nanomaterials has grown considerably over the past decade, building on prior fundamental studies demonstrating that a variety of redox-active metal complexes and organic species can be incorporated into metal-linked macrocycles and nanocages. This review provides an overview of this area of research, highlighting how different redox-active components affect the stability and functional properties of these structures. Important considerations for the design of redox-active nanostructures are described, such as the geometries, reduction potentials, and chemical properties of different components used to create these structures. The metal sites are often the limiting factor to the electrochemical stability of metal-organic assemblies, so special attention is paid to noting stability windows that have been identified for different types of metal components, including complexes of Pd, Pt, Re, Ru, Fe, and Co. Beyond these basic design considerations, this review highlights interesting emergent properties that arise from arranging multiple redox units in precise molecular nanostructures. In particular, recent developments in the redox-responsive host-guest chemistry and electrocatalytic activity of these structures are highlighted. • Experimental considerations for electrochemical studies of metal-organic nanocages. • Discussion of reduction potentials and stabilities of discrete metal-organic assemblies. • Recent advances in the functional properties of redox-active macrocycles and nanocages. • Electrocatalytic properties of nanocages and macrocycles. • Redox controlled host-guest chemistry.