A 66-Nuclear All-Alkynyl Protected Peanut-Shaped Silver(I)/Copper(I) Heterometallic Nanocluster: Intermediate in Copper-Catalyzed Alkyne-Azide Cycloaddition

Ligand-protected heterometallic nanoclusters in contrast to homo-metal counterparts show more broad applications due to the synergistic effect of hetero-metals but their controllable syntheses remain a challenge. Among heterometallic nanoclusters, monovalent Ag-Cu compounds are rarely explored due to much difference of Ag(I) and Cu(I) such as atom radius, coordination habits, and redox potential. Encouraged by copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction, comproportionation reaction of Cu(II)X and Cu(0) in the presence of (PhC≡CAg) complex and molybdate generated a core-shell peanut-shaped 66-nuclear Ag(I)-Cu(I) heterometallic nanocluster, [(MoO)@CuAg(PhC≡C)] (referred to as AgCu). The structure and composition of Ag-Cu heterometallic nanocluster are fully characterized. X-ray single crystal diffraction reveals that AgCu has a peanut-shaped silver(I)/copper(I) heterometallic nanocage protected by fifty phenylacetylene ligands in µ-modes and encapsulated two mutually twisted tetramolybdates. Heterometallic nanocage contains a 54-Ag-atom outer ellipsoid silver cage decorated by 12 copper inside wall. Nanosized AgCu is a n-type narrow-band-gap semiconductor with a good photocurrent response. Preliminary experiments demonstrates that AgCu itself and activated carbon supported AgCu/C are effective catalysts for 1,3-dipole cycloaddition between alkynes and azides at ambient conditions. The work provides not only a new synthetic route toward Ag(I)-Cu(I) nanoclusters but also an important heterometallic intermediate in CuAAC catalytic reaction.