Chiral Superatomic Nanoclusters Ag₄₇ Induced by the Ligation of Amino Acids

Silver nanoclusters containing Ag⁰ atoms protected by amino acids were synthesized and characterized. Chiral superatomic silver nanoclusters [Ag₄₇L₁₂(C≡C^tBu)₁₆]BF₄ (L=l-/d-valine or l-/d-isoleucine) have been prepared by reducing AgC≡C^tBu and amino acids (AAs) with NaBH₄. Single crystal X-ray diffraction revealed that these clusters have T symmetry, and the Ag₄₇ metal kernel can be viewed as a tetracapped truncated tetrahedron (Ag₁₇) surrounded with six W-shaped Ag₅ units. The clusters are homochiral as evidenced by CD measurements. As for the strong CD signals, large contributions are found from the occupied Ag s,p states (superatomic D states) near the Fermi level. Electron counting revealed that these clusters are 18-electron systems, suggesting they are superatomic clusters. The superatomic nature with a 1S²1P⁶1D¹⁰ configuration was supported by DFT calculations. This work paves the way of taking AAs as facile chiral induction agents for the synthesis of metal nanoclusters.