Silsesquioxane-Protected Silver Superatom

Silsesquioxanes as versatile organic-inorganic hybrids with terminal siloxyl sites have been utilized to construct diverse metallasilsesquioxane complexes, yet their niche in silver nanoclusters remains largely unexplored. Herein, we report the first silsesquioxane-protected superatomic silver nanocluster, [Ag₄₀(Ph₄Si₄O₈)₆(^tBuC≡C)₈] (Ag40), acquired through an "adaptive multipath synthesis" that circumvents the long-standing limitations imposed by hard and soft acids and bases principles in Ag(I) coordination chemistry. Single-crystal X-ray diffraction analysis reveals a kernel-shell architecture: a face-centered-cubic Ag₁₆⁸⁺ kernel, encapsulated by a [Ag₂₄(Ph₄Si₄O₈)₆] cage and ^tBuC≡C^- ligands. Synthetic methodology studies indicate that the macrocyclic all-cis-T₄: Ph₄Si₄O₈^4- ligands can be accessed via three distinct routes: in situ generation, pre-synthesis, and hierarchical-synthesis, all of which involve the hydrolytic condensation of PhSi(OR)₃ (R = Me, Et). Of these, the hierarchical approach addresses the limitations of the other two routes (poor stereochemical control in the in situ route and delayed supersaturation-induced slow crystallization in the pre-synthesis route), improving both the reproducibility and the growth efficiency of the Ag40 crystals. The mass spectrometry analysis not only provides compelling evidence for in situ transformation from cis,cis-T₃ to all-cis-T₄ ligands but also reveals the assembly pathways for the Ag₄₀ nanocluster either in pre-synthesis or in hierarchical-synthesis, underscoring the dynamic transformation of cyclic oligomeric silsesquioxanes and its critical role in capturing the ultrasmall subvalent silver kernel. Notably, Ag40 exhibits superatomic 1D→1P transition-dominated red phosphorescent emission, persisting in nondegassed solutions. As the highest-nuclearity oligosiloxane-capped metal cluster and first superatomic silver-silsesquioxane species, Ag40 establishes a paradigm for silica-supported superatom synthesis and advances hard-base-protected coinage metal nanoclusters.