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

The elaborate selection of the 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 CrO42-/tBuC≡C- co-capped Ag48 nanocluster (SD/Ag48, SD = SunDi) was synthesized and structurally characterized by single-crystal X-ray diffraction (SCXRD). The pseudo-fivefold symmetric metal skeleton of SD/Ag48 shows a core-shell structure comprised of an Ag23 cylin-der encircled by an outer Ag25 shell. Unprecedentedly, co-existence of inorganic (CrO42-) and organic (tBuC≡C-) ligands was observed on the surface of SD/Ag48. The inorganic CrO42- 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 CrO42- in the shape-control of silver nanoclusters.