Structural Isomerism in Bimetallic Ag20Cu12 Nanoclusters

Structural isomers of atomically precise metal nanoclusters are highly sought after for investigating structure–property relationships in nanostructured materials. However, they are extremely rare, particularly those of alloys, primarily due to the challenges in their synthesis and structural characterization. Herein, for the first time, a pair of bimetallic isomeric AgCu nanoclusters has been controllably synthesized and structurally characterized. These two isomers share an identical molecular formula, Ag 20 Cu 12 (C≡CR) 24 (denoted as Ag 20 Cu 12 -1 and Ag 20 Cu 12 -2; HC≡CR is 3,5-bis(trifluoromethyl)phenylacetylene). Single-crystal X-ray diffraction data analysis revealed that Ag 20 Cu 12 -1 possesses an Ag 17 Cu 4 core composed of two interpenetrating hollow Ag 11 Cu 2 structures. This core is stabilized by four different types of surface motifs: eight –C≡CR, one Cu(C≡CR) 2, one Ag 3 Cu 3 (C≡CR) 6, and two Cu 2 (C≡CR) 4 units. Ag 20 Cu 12 -2 features a bitetrahedron Ag 14 core, which is stabilized by three Ag 2 Cu 4 (C≡CR) 8 units. Interestingly, Ag 20 Cu 12 -2 undergoes spontaneous transformation to Ag 20 Cu 12 -1 in the solution-state. Density functional theory calculations explain the electronic and optical properties and confirm the higher relative stability of Ag 20 Cu 12 -1 compared to Ag 20 Cu 12 -2 . The controlled synthesis and structural isomerism of alloy nanoclusters presented in this work will stimulate and broaden research on nanoscale isomerism.