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, Ag₂₀Cu₁₂(C≡CR)₂₄ (denoted as Ag₂₀Cu₁₂-1 and Ag₂₀Cu₁₂-2; HC≡CR is 3,5-bis(trifluoromethyl)phenylacetylene). Single-crystal X-ray diffraction data analysis revealed that Ag₂₀Cu₁₂-1 possesses an Ag₁₇Cu₄ core composed of two interpenetrating hollow Ag₁₁Cu₂ structures. This core is stabilized by four different types of surface motifs: eight –C≡CR, one Cu(C≡CR)₂, one Ag₃Cu₃(C≡CR)₆, and two Cu₂(C≡CR)₄ units. Ag₂₀Cu₁₂-2 features a bitetrahedron Ag₁₄ core, which is stabilized by three Ag₂Cu₄(C≡CR)₈ units. Interestingly, Ag₂₀Cu₁₂-2 undergoes spontaneous transformation to Ag₂₀Cu₁₂-1 in the solution-state. Density functional theory calculations explain the electronic and optical properties and confirm the higher relative stability of Ag₂₀Cu₁₂-1 compared to Ag₂₀Cu₁₂-2. The controlled synthesis and structural isomerism of alloy nanoclusters presented in this work will stimulate and broaden research on nanoscale isomerism.