Overcoming the Crystallization Bottleneck: A Family of Gigantic Inorganic {Pdx}L (x=84, 72) Palladium Macrocycles Discovered using Solution Techniques

The {Pd-84}(Ac) wheel, initially discovered serendipitously, is the only reported giant palladium macrocyclea unique structure that spontaneously assembles from small building blocks. Analogues of this structure are elusive. A new modular route to {Pd-84}(Ac) is described, allowing incorporation of other ligands, and a new screening approach to cluster discovery. Structural assignments were made of new species from solution experiments, overcoming the need for crystallographic analysis. As a result, two new palladium macrocycles were discovered: a structural analogue of the existing {Pd-84}(Ac) wheel with glycolate ligands, {Pd-84}(Gly), and the next in a magic number series for this cluster familya new {Pd-72}(Prop) wheel decorated with propionate ligands. These findings confirm predictions of a magic number rule for the family of {Pd-x} macrocycles. Furthermore, structures with variable fractions of functional ligands were obtained. Together these discoveries establish palladium clusters as a new class of tunable nanostructures. In facilitating the discovery of species that would not have been discovered by orthodox crystallization approaches, this work also demonstrates the value of solution-based screening and characterization in cluster chemistry, as a means to decouple cluster formation, discovery, and isolation.