Synthesis, Structure, Anion-Driven Reorganization, and Catalytic Activity of Pt1Ag21 Nanocluster Featuring a Defective Icosahedral Pt1Ag9 Core

Atomically precise metal nanoclusters (NCs) are ideal model systems for elucidating the principles of cluster structural transformation and establishing structure–activity relationships. Herein, we successfully synthesize a multiligand-co-protected 6-electron nanocluster, Pt1Ag21(Dppm)4(S-Adm)10Cl3, which possesses a distorted defective icosahedral Pt1Ag9 kernel. Upon induction by the weakly coordinating SbF6– anion, the cluster undergoes structural reconstruction and transforms into an 8-electron nanocluster Pt1Ag31(Dppm)3(S-Adm)16(DppmO)Cl3 with a perfect icosahedral Pt1Ag12 core. Single-crystal X-ray diffraction (SC-XRD) precisely resolves the full atomic structures of both clusters and clearly illustrates the atomic-level evolution pathway from the defective Pt1Ag9 kernel to the intact Pt1Ag12 kernel. Characterizations via ultraviolet–visible (UV–vis) absorption spectroscopy combined with theoretical calculations verify that structure reconstruction remarkable regulatory effects on the optical absorption features, energy level structures of the clusters. For catalytic investigations, Pt1Ag21 and Pt1Ag31 are immobilized on carbon nanotubes to afford Pt1Ag21@CNT and Pt1Ag31@CNT composite catalysts, which are systematically evaluated in the Knoevenagel condensation of benzaldehyde with malononitrile. The two supported catalysts display distinct, structure-dependent catalytic behaviors: Pt1Ag21@CNT reaches its maximum yield (95%) in MeOH at 30 °C, whereas Pt1Ag31@CNT performs best (95%) in EtOH at 40 °C. This crossover of the optimal operating windows reflects their differences in kernel structure, valence-electron count and frontier electronic structure. This research further enriches the anion-regulation platform for precisely tailoring the atomic structures and catalytic functions of metal nanoclusters.