[Ag48(C≡CtBu)20(CrO4)7]: An Atomically Precise Silver Nanocluster Co-protected by Inorganic and Organic Ligands

The elaborate selection of capping ligands is of great importance in the synthesis of atomically precise metal nanoclusters. Organic thiolates, alkynyls, phosphines, and/or their combinations are the ligands most widely utilized to protect metal nanoclusters, while inorganic oxo anions have been almost neglected in this field. Herein, the first CrO₄^2-/ ^tBuC≡C^- co-capped Ag₄₈ nanocluster (SD/Ag48, SD = SunDi) was synthesized and structurally characterized by single-crystal X-ray diffraction. The pseudo-5-fold symmetric metal skeleton of SD/Ag48 shows a core-shell structure composed of a Ag₂₃ cylinder encircled by an outer Ag₂₅ shell. Unprecedentedly, coexistence of inorganic (CrO₄^2-) and organic ( ^tBuC≡C^-) ligands was observed on the surface of SD/Ag48. The inorganic CrO₄^2- anion plays three important roles in the construction of silver nanoclusters: (i) passivating the Ag₂₃ kernel; (ii) connecting the core and shell; and (iii) protecting the Ag₂₅ shell. This nanocluster belongs to a 14e superatom system and exhibits successive molecule-like absorption bands from the visible to the ultraviolet region. This work not only establishes a fresh inorganic ligand strategy in the synthesis of silver nanoclusters but also provides a new insight into the important surface coordination chemistry of CrO₄^2- in the shape control of silver nanoclusters.