Abstract
Understanding and controlling the assembly of mechanically interlocked molecules remains a significant challenge. Formation of mechanically interlocked metal-organic cages has, to date, relied exclusively on transition metals due to their predictable coordination geometries and robust bonding. Here, we report, for the first time, the reversible assembly of mechanically interlocked cages based on main-group metals, Al(6)L(4) and Ga(6)L(4). Structural and computational analyses reveal helical [2]catenane quadruple-decker cage topologies stabilized by six metal-ligand nodes, bridging μ-OH groups, extensive π-stacking, and directional CH⋯O interactions. Remarkably, simple acid-base cycling triggers fully reversible cage unlocking-recatenation processes in water at room temperature. Unlike transition-metal-mediated cage interlocking, they assemble instantaneously and selectively via an unprecedented cooperative main-group interlocking pathway, without detectable monomeric cage intermediates. Thermodynamic analyses reveal metal-dependent switching, involving entropy-driven disassembly coupled to strongly enthalpy-driven reassembly, with the Ga(6)L(4) cage ∼500-fold more stable than Al(6)L(4). These findings provide fundamental understanding of new assembly dynamics beyond conventional transition metals.