The Effect of Allosteric Conformational Regulation on the Crystal Packing of Aromatic Amide Metallomacrocycles via Ligand-Modulated Remote Intramolecular Hydrogen Bonds

The versatility of supramolecular chemistry stems from rational molecular design, which allows for the precise control over noncovalent interactions to direct self-assembly processes. Inspired by allosteric regulation in biomolecules, where long-range interactions dictate function, we report a novel aramide macrocyclic palladium complex that adopts distinct conformations upon allosteric complexation with ligands based on 4-substituted pyridine derivatives. Modulating ligand coordination strength and steric demand alters intramolecular three-center hydrogen-bond strength at a remote site, leading to inversion of the orientations of remote amide groups. This approach affords direct control over macrocyclic conformation in the solid state, allowing reversible transition between chairlike conformers with weakly coordinated ligands and V-shaped conformers with strongly coordinated ligands. Crucially, this conformational control, achieved through local binding events, i.e., atomic-level ligand exchange, while preserving the macrocyclic integrity, not only propagates to the supramolecular level but also sequentially modulates crystal packing, ultimately guiding the formation of higher-order structures driven by the precise columnar and layered arrangement of the palladium complex.