Ag14 Nanocluster Featuring an Unconventional Non-FCC Metal Skeleton and Its Sensitivity to Oxygen

Despite the significant advancements in noble metal-based nanocluster research, challenges remain in making specific metal kernel geometries, especially protected by bulky ligand shells. Here, we synthesized and structurally characterized a neutral silver cluster, [Ag14(TRZ)12(TPP)3], where TRZ and TPP refer to 6-(dibutylamino)-1,3,5-triazine-2,4-dithiolate and triphenylphosphine, respectively. The cluster was synthesized under ambient conditions using a TPP-assisted, solvent-mediated structural transformation from the [Ag31(TRZ)10]2- precursor cluster. This non-face-centered cubic (non-fcc) cluster features a central Ag5 trigonal bipyramidal core surrounded by a distinct Ag(6+3) tricapped trigonal prismatic (TTP) shell. This type of unconventional metal skeleton differs significantly from the well-known fcc-type Ag14 cluster, which typically has an octahedral Ag6 core and a cubic Ag8 shell. It is also the first metal cluster to be structurally resolved with TRZ ligands. Quantum chemical calculations indicate that although the non-fcc Ag14 skeleton has a lower cohesive energy than the fcc Ag14 analogues, bulky TRZ ligands featuring multiple sulfide linkages and n-butyl chains stabilize it. The as-synthesized Ag14 cluster is non-emissive, but exposure to oxygen converts it into an orange-emitting species. Density functional theory calculations indicate that the TTP Ag(6+3) shell prefers binding with oxygen. Emissive lifetime and femtosecond transient absorption showed that oxygenation provided greater stabilization of excited states than the parent Ag14 cluster. This study presents a new approach for designing metal clusters with unique structural frameworks with unconventional ligand environments and allows for harvesting surface-sensitive electronic properties.