Golden Opportunity: A Clickable Azide-Functionalized [Au25(SR)18]-Nanocluster Platform for Interfacial Surface Modifications

Ultrasmall atomically precise monolayer-protected gold thiolate nanoclusters are an intensely researched nanomaterial framework, but there is a lack of a system that can be directly synthesized and undergo interfacial surface chemistry. We report an [Au<sub>25</sub>(SCH<sub>2</sub>CH<sub>2</sub>-<i>p</i>-C<sub>6</sub>H<sub>4</sub>-N<sub>3</sub>)<sub>18</sub>]<sup>-</sup> nanocluster platform with azide moieties appended onto <i>each </i>surface ligand. The structure of this surface reactive cluster has been confirmed by single-crystal X-ray crystallography, mass spectrometry and UV-Vis, IR and NMR spectroscopies. We show that <i>all</i> surface azide moieties are amenable to cluster-surface strain-promoted alkyne-azide cycloaddition (CS-SPAAC) chemistry with a strained cyclooctyne, opening this as a new <i>platform </i>to allow functional, post-assembly surface modifications to this very prominent nanocluster.