Ag44(SR)304−: a silver-thiolate superatom complexElectronic supplementary information (ESI) available: Extended mass spectra and SV-AUC data. See DOI: 10.1039/c2nr30773a

Intensely and broadly absorbing nanoparticles (IBANs) of silver protected by arylthiolates were recently synthesized and showed unique optical properties, yet question of their dispersity and their molecular formulas remained. Here IBANs are identified as a superatom complex with a molecular formula of Ag 44 (SR) 30 4− and an electron count of 18. This molecular character is shared by IBANs protected by 4-fluorothiophenol or 2-naphthalenethiol. The molecular formula and purity is determined by mass spectrometry and confirmed by sedimentation velocity-analytical ultracentrifugation. The data also give preliminary indications of a unique structure and environment for Ag 44 (SR) 30 4− . Intensely and broadly absorbing nanoparticles protected by arylthiolates are identified as Ag 44 (SR) 30 4− , a monodisperse silver-thiolate superatom complex.