[Ag 15 (N-triphos) 4 (Cl 4 )](NO 3 ) 3 : a stable Ag-P superatom with eight electrons (N-triphos = tris((diphenylphosphino)methyl)amine).

A first and stable Ag-P superatom nanocluster [Ag15 (N-triphos)4 (Cl4 )](NO3 )3 (1) has been successfully synthesized and characterized. X-ray analysis shows that this Ag15 cluster has a hexacapped body-centered cubic (bcc) framework which is consolidated by four tripodal N-triphos ligands. The identity of 1 is confirmed by high resolution ESI-MS. Cluster 1 has an electronic and geometric shell closure structure with 8 free electrons, matching the stability idea of superatom theory for a nanocluster. DFT calculation of this Ag15 cluster reveals the superatom feature with a 1S2 1P6 configuration. The chelation of multidentate phosphines enhances the stability of this Ag15 cluster. The AgAg distances between the centered and the vertical Ag atoms of this bcc (Ag@Ag8 ) are in the range of 2.57-2.71 Å, and the distances between the face-capped and the vertical silver atoms are in the range of 2.84-2.92 Å, showing strong AgAg interactions within this cluster core. This superatom complex exhibits a relatively high thermal and photolytic stability.