Isomeric Au₇Cu₈ Nanoclusters With Identical Building Blocks but Distinct Assembly Modes

Isomeric metal nanoclusters composed of identical building blocks provide an ideal platform for probing structure-property relationships at the atomic level; however, their controlled synthesis remains highly challenging. Herein, we report the synthesis and structural characterization of two structurally isomeric AuCu nanoclusters, [Au₇Cu₈(L)₂(TBA)₄Cl₆]PF₆ (L = PNP or PMNP, where PNP is 2,6-bis(diphenylphosphino)pyridine, PMNP is 2,6-bis(diphenylphosphinomethyl)pyridine, and TBA is tert-butylacetylide), denoted as Au₇Cu₈-1 and Au₇Cu₈-2, respectively. Single-crystal X-ray diffraction analysis reveals that both isomers feature an Au₇Cu₆ core constructed from two pentagonal bipyramidal Au₄Cu₃ building blocks fused through a common Au atom. The two isomers differ in the assembly mode of the Au₄Cu₃ units: in Au₇Cu₈-1, fusion occurs through a gold atom at a vertex of the equatorial pentagon, whereas in Au₇Cu₈-2, it occurs through an apical gold atom. Notably, Au₇Cu₈-1 exhibits intense near-infrared phosphorescence at 752 nm with a photoluminescence quantum yield of 26.2% in solution, whereas Au₇Cu₈-2 is non-emissive. Theoretical calculations reveal distinct electronic structures and excited-state relaxation pathways for the two isomers, providing microscopic insight into their different photoluminescence behaviors. These findings deepen our understanding of how structural isomerism influences the electronic structures and photophysical properties of metal nanoclusters.