Isolation of Homo-/Mixed-Valence Ag12, Ag29, and Ag8 Clusters Stabilized by Cyclic Alkyl(amino) Carbene-Anchored Monoanionic Phosphorus Ligand

Silver clusters are attractive candidates for their promising optical properties, and biomedical activities. Herein, we report on the first syntheses and isolation of three homo-/mixed-valence silver nanoclusters (NCs) with Ag12Cl3, Ag-29, and Ag-8 cores [((cAAC)P)(6)Ag12Cl3](OTf)(3) (1), [((cAAC)P)(6)Ag-29] (2), and [((cAAC)P)(4)Ag-8] (3) having three-/twofold symmetry, employing cyclic alkyl(amino) carbene (cAAC)-supported phosphinidenide (cAACP(-)) as the pi-accepting stabilizing ligand. The average diameters of Ag NCs 1, and 2 are approximately 1.6 to 2 nm. The redox non-innocent mono-atomic phosphorus anions (P-) anchored with cAAC ligands are generated in situ by the reaction of AgOTf with a boryl-phosphaalkene (cAAC)P-B((NPr2)-Pr-i)(2) through cleavage of the P-B bond with the help of a triflate anion (OTf-) as a weak nucleophile. Equivalent number of the (cAAC)P- anions generated in situ are oxidized to produce the corresponding bis-phosphinidene (cAAC)(2)P-2 leading to the generation of Ag-0 ions in solution for the formation of the unprecedented mixed-valence Ag NC 2. Complex 3 is achieved by treating potassium phosphinidenide cAACPK with AgNTf2. The ligand field and the steric hindrance of the (cAAC)P units play crucial roles in stabilizing complexes 1-3, further providing a three- (1, 2)/two- (3) fold stand. The Ag12Cl3 NC (1) with a tricationic core [(Ag12Cl3)-Cl-I] was found to be diamagnetic, and fluorescent, emitting green light at 563 nm when excited at 400 nm. In contrast, the neutral Ag-29 (2) and Ag-8 (3) clusters were found to be paramagnetic, and NMR silent showing characteristic EPR signals for Ag-0 at room temperature.

Automated summary

This study reports on the synthesis and isolation of silver nanoclusters with Ag12Cl3, Ag-29, and Ag-8 cores for the first time. It was found that these clusters exhibit different magnetic and optical properties.