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

Abstract

The {Pd84 }(Ac) wheel, initially discovered serendipitously, is the only reported giant palladium macrocycle-a unique structure that spontaneously assembles from small building blocks. Analogues of this structure are elusive. A new modular route to {Pd84 }(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 {Pd84 }(Ac) wheel with glycolate ligands, {Pd84 }(Gly) , and the next in a magic number series for this cluster family-a new {Pd72 }(Prop) wheel decorated with propionate ligands. These findings confirm predictions of a magic number rule for the family of {Pdx } 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.

Keywords: ion mobility; palladium; polyoxopalladates; self-assembly; size exclusion.