Threading an Aluminum Molecular Ring Onto a Chemically Growing Copper-Directed Polyrotaxane.

Controlled assembly of advanced mechanically interlocked architectures remains a major challenge in supramolecular chemistry. Inspired by the hard and soft acids and bases principle, we present a modular and hierarchical strategy for the synthesis of aluminum-based mechanically interlocked molecules (AlMIMs) assembled from four synergistic components. Aluminum ions generate robust macrocyclic frameworks through coordination with aromatic carboxylates, while adaptive nitrogen-donor ligands, in concert with structure-directing copper ions, promote axle threading and govern structural dimensionality. This approach creates a full structural library, from discrete [2]- and [3]rotaxanes to extended polyrotaxane networks, demonstrating broad versatility. Within the spatially confined macrocyclic cavity, copper ions preferentially adopt a stable linear coordination geometry while remaining conformationally flexible outside the cavity to accommodate diverse coordination modes and aggregation states. This dual behavior cooperatively facilitates highly ordered assembly. Notably, the resulting AlMIMs exhibit remarkably enhanced third-order nonlinear optical responses, highlighting emergent properties arising from mechanical interlocking. This work underscores the power of merging coordination chemistry with supramolecular design, transcending conventional static paradigms by revealing how metal ion coordination can be dynamically modulated within precisely engineered supramolecular environments.