Orthogonal Selection and Fixing of Coordination Self-Assembly Pathways for Robust Metallo-organic Ensemble Construction

Supramolecular construction strategies have overwhelmingly relied on the principles of thermodynamic control. While this approach has yielded an incredibly diverse and striking collection of ensembles, there are downsides, most obviously the necessity to trade-off reversibility against structural integrity. Herein we describe an alternative "assembly-followed-by-fixing" approach that possesses the high-yielding, atom-efficient advantages of reversible self assembly reactions, yet gives structures that possess a covalent-like level of kinetic robustness. We have chosen to exemplify these principles in the preparation of a series of M2L3 helicates and M4L6 tetrahedra. While the rigidity of various bis(bidentate) ligands causes the larger species to be energetically preferred, we are able to freeze the self-assembly process under "non-ambient" conditions, to selectivity give the disfavored M2L3 helicates. We also demonstrate "kinetic-stimuli" (redox and light)-induced switching between architectures, notably reconstituting the lower energy tetrahedra into highly distorted helicates.