Structural Isomerism in Bimetallic Ag 20 Cu 12 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.