An Atomically Precise Alkynyl-Functionalized Silver–Polyoxotungstate Nanocluster with Sandwiched Three-Layer {Ag₁₃}¹³⁺ Cluster Architecture and Enhanced Antitumor Activity

The synthesis of atomically precise, structurally well-defined polyoxometalate (POM)-stabilized silver clusters with accessible silver surfaces remains a significant challenge. Here, we report an alkynyl-functionalized silver–POM hybrid nanocluster, [(n-Bu)₄N]₇[(C₆H₉)₆(PW₁₁O₃₉)₂Ag₁₃] ((PW₁₁)₂-Ag₁₃), which comprises of a distinctive homovalent three-layer {Ag₁₃}¹³⁺ cluster. This architecture yields a lower HOMO − LUMO energy gap of 1.93 eV, compared to the precursor [PW₁₁O₃₉]⁷⁻ (2.74 eV). Structural characterization and theoretical calculations confirm that the lacunary [PW₁₁O₃₉]⁷⁻ and alkynyl units direct the formation of the atomically precise {Ag₁₃}¹³⁺ cluster, preventing undesirable silver aggregation while maintaining exposed silver surfaces that are crucial for catalytic activity. The synergistic redox capabilities of the POM and silver components enhance the redox reactivity of (PW₁₁)₂-Ag₁₃, promoting efficient reactive oxygen species (ROS) generation via a Fenton-like mechanism. Additionally, biological evaluations further reveal that (PW₁₁)₂-Ag₁₃ exhibits significantly superior antitumor activity than [PW₁₁O₃₉]⁷⁻, primarily through ROS-induced apoptosis facilitated by the active silver cluster sites. These findings highlight the potential of silver cluster-POM hybrids as promising candidates for anticancer therapeutic applications.