Diversification of heteroleptic assembly topologies through covalent bridging

Expanding the structural and functional diversity of metallosupramolecular assemblies remains challenging for selective recognition, catalysis, and materials science. Existing synthetic strategies often impose constraints on the size, shape, and functionalization of building blocks, limiting access to assemblies of certain geometries or higher nuclearity. Here, we demonstrate a versatile approach for accessing a variety of heteroleptic, metal-mediated architectures based on the covalent bridging of identical or unlike ligands via flexible or rigid tethers, thus enabling synthetic routes to previously unattainable di- and tetranuclear multicomponent structures. Depending on the type of bridge and counter-ligand combination, we achieved the non-statistical assembly of Pd 2 (AB)CD cages, singly-bridged Pd 4 A 4 (B 2 )D 2 double-cavity systems and doubly-bridged Pd 4 (B 2 ) 2 D 2 structures. Dynamic cage-to-cage transformations enable triggered separation of C 60 from fullerene mixtures, while incorporation of photoswitchable ligands allows reversible modulation of cage geometry and properties. Remarkably, all assemblies arise from ligands that, in their untethered form, fail to yield clean integrative self-sorting. The robustness of this modular strategy is demonstrated through comprehensive NMR spectroscopic and mass spectrometric characterization and six single-crystal X-ray structures. Methodological progress in the synthetic access to nanostructures of increasing complexity promises to advance the functionality of soluble receptors, stimuli-responsive life-like systems and porous materials with intricate morphology.