Structural Isomerism in Bimetallic Ag20Cu12 Nanoclusters

Abstract

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 equivalent to CR)(24) (denoted as Ag20Cu12-1 and Ag20Cu12-2; HC equivalent to 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 equivalent to CR, one Cu(C equivalent to CR)(2), one Ag3Cu3(C equivalent to CR)(6), and two Cu-2(C equivalent to CR)(4) units. Ag20Cu12-2 features a bitetrahedron Ag-14 core, which is stabilized by three Ag2Cu4(C equivalent to 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.