Design of Metal-Organic Assemblies via Shape Complementarity and Conformational Constraints in Dual Curvature Ligands

While common in biological systems, building blocks with low symmetry and flexibility pose numerous problems for synthetic self-assembly, such as the formation of isomers of assemblies that are difficult to distinguish and purify. In this work, three aromatic amide-based ligands ( L1– L3) with a central 1,8-diazatriptycene core were designed and used for self-assembly with Pd²⁺. While hundreds of stereoisomers based on the conformational flexibility around the amides and the unsymmetrical nonplanar structure of the core are possible upon coordination with the metal, the constraints designed into the ligands direct the self-assembly toward only a single Pd₂L₄ cage ( L1) or Pd₄L₈ double-walled metallomacrocycle ( L2) structure, even in mixtures of the ligands. This structural approach and the modularity of the ligand synthesis affords ready access to deep cavitands with endohedral functionalization ( L3). These results highlight the potential of this new design strategy and open the door to selectively functionalized cavity-based architectures for numerous applications.