α-Hydroxyalkynyl-protected copper( i ) acetelyenediide nanoclusters with anion-dependent photoluminescence

Photoluminescent copper(I) acetelyenediide nanoclusters [(C₂)Cu₁₅(CCC(OH)R₂¹)₁₀(ClO₄)₂(CH₃OH)₃](ClO₄) (Cu15, HCCC(OH)R₂¹ = ethinylestradiol) and [(C₂)Cu₁₇(CCC(OH)R₂²)₁₀(CF₃CO₂)₅] (Cu17, HCCC(OH)R₂² = ethisterone) are synthesised via comproportionation reactions of Cu(0) powder and Cu(II) salts in methanol. The employed α-hydroxyalkynes not only form multidentate α-hydroxyalkynyl ligands to stabilise the clusters from outside, but also release acetelyenediide (C₂^2-) under ambient conditions in situ to template the formation of clusters from inside. Notably, although Cu15 and Cu17 share quite similar overall structures, the latter exhibits a photoluminescence quantum yield (PLQY) 15 times higher than the former in ethanol. A full and rigid protection formed by inner μ₉-C₂^2-, outer μ₅-CCC(OH)R₂² ligands, and bridging CF₃CO₂^- anions in Cu17 is responsible for such significantly enhanced photoluminescence, as confirmed by theoretical calculations. This work demonstrates a mixed inner-outer and hetero-multidentate-ligand strategy for synergistically stabilising metal nanoclusters and generating intense photoluminescence, and α-hydroxyalkynes are highly applicable in achieving alkynyl-protected metal acetelyenediide clusters in a two birds, one stone manner.