On the Structural Adaptability and Dynamics of Metal-Organic Cages
Metal-organic cages are molecular receptors that enable selective molecular recognition and catalysis, yet most current cage systems employ rigid building blocks that limit guest accommodation and environmental adaptability. Developing cages that combine structural integrity with conformational adaptability remains challenging, requiring balance between pre-organisation for discrete assembly and flexibility for responsive behaviour. This thesis explores dynamic and adaptive metal-organic cage systems through strategic incorporation of flexible subcomponents. Three approaches demonstrate how adaptive self-assembly, dynamic structures, and structural transformations enhance supramolecular host functionality. The first approach introduces a conformationally adaptable ZnII₈L₆ pseudo-cubic cage with tetramine subcomponents featuring 2,6-naphthylene rotary units. These enable independent face switching between endo and exo conformations, dynamically expanding cavity volume to accommodate guests ranging from 46 to 154% of the initial cavity size. The system exemplifies Koshland's induced-fit model, demonstrating synthetic assemblies can mimic biological macromolecule adaptability while maintaining structural integrity. The second approach extends this adaptability to the self-assembly of heteroleptic cages, using the same adaptive tetramine to match triangular building blocks of increasing size. This generates three distinct ZnII₆L₃L'₂ triangular prismatic cages with conformations from near-equilateral to elongated geometries. The 2,6-naphthylene units provide geometric flexibility enabling adaptive matching with assembly partners, accessing heteroleptic structures of distinct sizes. The third approach investigates CuI cages transforming between [CuI₁₂L₆]¹²⁺ pseudo-hexagonal prismatic and [CuI₈L₄]⁸⁺ tetragonal tubular structures. Using 1,5-naphthylene-bearing tetramine subcomponents to promote secondary interactions, the study reveals that these interactions may collectively template complex structures, while introducing or removing steric hindrance to block these interactions can direct the system towards formation of or transformation to different structures. These studies establish design principles for engineering adaptive behaviour into metal-organic cages. The cage systems presented demonstrate that adaptability can influence either the conformation of individual structures or direct the formation and transformation of multiple structures. The principles enable more efficient and versatile design of molecular receptors, opening applications in molecular recognition, separation, catalysis, and sensing while bridging synthetic and biological system capabilities.
Self-assembly, Supramolecular chemistry, Metal-organic cages, Coordination chemistry, Host-guest chemistry, Molecular capsules, Coordination cages
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