Two pure silver nanoparticles (Ag-210((PrPhS)-Pr-i)(71)(Ph3P)(5)Cl and Ag-211((PrPhS)-Pr-i)(71)(Ph3P)(6)Cl labeled as SD/Ag210 and SD/Ag211 (SD=SunDi), were found to co-crystallize in forming compound 1. Single-crystal X-ray diffraction (SCXRD) revealed that they differ by only one Ag(PPh3). Their four-shell nanoparticles consist of three pure Ag metal shells (Ag-19@Ag-52@Ag-45) shielded by a silver-organic Ag-89((PrPhS)-Pr-i)(71)Cl[Ag(Ph3P)](n) outermost shell. The number (n) of Ag(Ph3P) is five for SD/Ag210 and six for SD/Ag211. The pseudo-fivefold symmetric Ag nanoparticles exhibit surface plasmon absorption similar to a true metallic state but at the nanoscale. This work exemplifies the important effects of phosphine in stabilizing large silver nanoparticles; and offers a platform to investigate the origin of differences in nanoscale metal materials, even differing by only one metal atom; it also sheds light on the regioselective binding of auxiliary Ph3P on the surface of silver nanoparticles.