Synthesis and Surface Modification of Azide Decorated Silver Nanoclusters

Alexander H. Stöckli, The University of Western Ontario

Abstract

In nanocluster research, easy modification of the cluster surface while maintaining the cluster core remains a key challenge. Herein we report the synthesis, structure, and properties of four targeted Ag₂₀ nanoclusters (NCs) with surface azide moieties, two of which have 8 azide moieties, [CO₃@Ag₂₀(S^tBu)₁₀(m-N₃-C₆H₄COO)₈(DMF)₄] and [CO₃@Ag₂₀(S^tBu)₁₀(p-N₃-C₆H₄COO)₈(DMF)₄], and two of which have 6 azide moieties, [CO₃@Ag₂₀(S^tBu)₁₀(m-N₃-C₆H₄COO)₆(NO₃)₂(DMF)₄] and [CO₃@Ag₂₀(S^tBu)₁₀(p-N₃-C₆H₄COO)₈(NO₃)₂(DMF)₄]. These Ag₂₀ NCs with surfaces azide moieties are the first examples of Ag nanoclusters that can undergo cluster surface strain-promoted azide alkyne cycloaddition (CS-SPAAC) click reactions, introducing new functionality to the cluster surface. Reactivity was screened on the 8-azide NCs using a model strained cyclooctyne framework in exo-bicyclo[6.1.0]non-4-yn-9-ylmethanol (BCN) and a ferrocene functionalized derivative. Reaction products and parent clusters were characterized by UV-Vis., FT-IR, and NMR spectroscopies. The structure of the parent clusters and presence of surface azides was further confirmed by SCXRD analysis and XPS. Both tested clusters were found to be amenable to CS-SPAAC reactions with retention of the NC frameworks.