Revealing the chirality origin and homochirality crystallization of Ag14 nanocluster at the molecular level

Although chirality is an ever-present characteristic in biology and some artificial molecules, controlling the chirality and demystifying the chirality origin of complex assemblies remain challenging. Herein, we report two homochiral Ag-14 nanoclusters with inherent chirality originated from identical rotation of six square faces on a Ag-8 cube driven by intra-cluster pi center dot center dot center dot pi stacking interaction between pntp(-) (Hpntp = p-nitrothiophenol) ligands. The spontaneous resolution of the racemic (SD/rac-Ag14a) to homochiral nanoclusters (SD/L-Ag14 and SD/R-Ag14) can be realized by re-crystallizing SD/rac-Ag14a in acetonitrile, which promotes the homochiral crystallization in solid state by forming C-H center dot center dot center dot O/N hydrogen bonds with nitro oxygen atoms in pntp(-) or aromatic hydrogen atoms in dpph (dpph = 1,6-bis(diphenylphosphino)hexane) on Ag-14 nanocluster. This work not only provides strategic guidance for the syntheses of chiral silver nanoclusters in an all-achiral environment, but also deciphers the origin of chirality at molecular level by identifying the special effects of intra- and inter-cluster supramolecular interactions. The preparation of chiral monolayer-protected metal clusters is interesting for their potential applications in a variety of fields, including catalysis. Here, the authors synthesize chiral Ag-14 nanoclusters in an all-achiral environment, and decipher the origin of chirality at the molecular level; the solvent choice is key to achieve homochiral crystallization.

Automated summary

The study reports two homochiral Ag-14 nanoclusters with inherent chirality originated from intra-cluster pi center dot center dot center dot pi stacking interaction between ligands. The racemic mixture can be spontaneously resolved into homochiral nanoclusters by re-crystallizing in acetonitrile, highlighting the importance of solvent choice in achieving homochiral crystallization.