The molecular formulas and charge state distributions of thus-far known ubiquitous alkanethiolate-protected gold clusters with core-masses of 8 and 29 kDa were assessed using electrospray ionization mass spectrometry. The 8 and 29 kDa clusters were determined to be composed of single species, [Au38(SCn)24]z and [Au144(SCn)59]z, respectively, with charge states of z >/= 0. Possible geometric structures for Au38(SCn)24 and Au144(SCn)59 are discussed, based on the structures of relevant systems that have been recently determined experimentally and theoretically: [Au25(SR)18]- and Au102(SR)44, in which the Au cores are protected by monomers [-SR-Au-SR-] and/or dimers [-SR-Au-SR-Au-SR-]. Their preferential formation and chemical robustness are proposed as being associated with high stability due to geometric factors, while the Au-thiolate interface takes on common motifs regardless of the underlying Au core.

Phosphine-stabilized Au11 clusters in chloroform were reacted with glutathione (GSH) in water under a nitrogen atmosphere. The resulting Au:SG clusters exhibit an optical absorption spectrum similar to that of Au25(SG)18, which was isolated as one of the major products from chemically prepared Au:SG clusters (Negishi, Y. et al. J. Am. Chem. Soc. 2005, 127, 5261). Rigorous characterization by optical spectroscopy, electrospray ionization mass spectrometry, and polyacrylamide gel electrophoresis confirms that the Au25(SG)18 clusters were selectively obtained on the sub-100 mg scale by ligand exchange reaction under aerobic conditions. The ligand exchange strategy offers a practical and convenient method of synthesizing thiolated Au25 clusters on a large scale.

A. Optical Absorption SpectraFigure S1. Optical absorption spectra of [Au 25 (PPh 3 ) 10 (SC n H 2n+1 ) 5 Cl 2 ] 2+ in ethanol.

Size matters: The core‐etching reaction by free glutathione is studied for glutathionate (SG)‐protected Aun(SG)m clusters with n=10–39 and m=10–24 (see picture). Only the Au25(SG)18 clusters remain unetched, whereas the Aun(SG)m clusters with n<25 and n>25 are transformed into a AuI:SG complex and stable Au25:SG, respectively. The selective synthesis of thiolate (SR)‐protected Au25:SR on a large scale may be possible.

The present work aims to test the validity of the electronic shell model for Au25(SC6H13)18 by monitoring the charge state of the Au:S core and thereby to elucidate the origin of magic stability. Electrospray ionization mass spectrometry revealed that the Schiffrin method yields [Au25(SC6H13)18] x with a distribution of charge states, which shifts toward negative values with reduction time. The stable ions [Au25(SC6H13)18]1+ and [Au25(SC6H13)18] - can be synthesized by chemical oxidation and reduction of [Au25(SC6H13)18]0, respectively. These findings lead us to conclude that electronic shell closing is not a crucial factor for the high stability of [Au25(SC6H13)18] x (x = 1−, 0, 1+). We ascribe magic stability to the core-in-cage structure predicted theoretically.

A magic‐number Au13 cluster with icosahedral geometry can be exclusively generated from a polydisperse mixture of ultrasmall 1,2‐bis(diphenylphosphino)ethane‐coordinated gold clusters upon treatment with HCl, which acts as an efficient promoter.

Cores and effect: A post‐synthetic approach using a diphosphine ligand gave two Au8 clusters with unique core geometries based on edge‐shared gold tetrahedron motifs (see picture). Although the clusters have isomeric cores, they have different colors and different optical properties. These differences are shown to depend on the core geometries.

Over recent years, research on the structures and properties of ligand-protected gold cluster molecules has gained significant interest. The crystal structure information accumulated to date has revealed the structural preference to adopt closed polyhedral geometries, but the use of multidentate ligands sometimes leads to the formation of exceptional structures. This Account describes results of our studies on diphosphinecoordinated [core+exo]-type gold clusters featuring extra gold atoms outside the polyhedral cores, highlighting (1) their distinct optical properties due to the unique electronic structures generated by the exo gold atoms and (2) electronic/attractive ligand−cluster interactions that cause definite perturbation effects on the cluster properties. Subnanometer gold clusters with [core+exo]-type geometries (nuclearity = 6, 7, 8, and 11) commonly displayed single absorption bands in the visible region, which are distinct in patterns from those of conventional polyhedral-only homologues. Theoretical studies demonstrated that the exo gold atoms are critically involved in the generation of unique electronic structures characterized by the HOMO−LUMO transitions with dominant oscillator strengths, leading to the appearance of the isolated absorption bands. On the basis of the frontier orbital distributions, the HOMO and LUMO were shown to be localized around the polyhedral cores and exo gold atoms, respectively. Therefore, the HOMO−LUMO transitions responsible for the visible absorptions occur in the core → exo direction. The HOMO−LUMO gap energies showed no clear trends with respect to the nuclearity (size), indicating that the individual geometric features of the inorganic framework primarily govern the clusters' electronic structures and properties. Systematic studies using octagold clusters bearing various anionic coligands revealed that electronic or attractive interactions between the gold framework and ligand functionalities, such as π-electron systems and heteroatoms, cause substantial perturbations of the wavelength of the visible absorption band due to the HOMO−LUMO transitions. Especially, significant red shifts were observed as a result of the electronic coupling with specific π-resonance contributors. It was also found that the orientation of aromatic rings around the inorganic framework is a factor that affects the cluster photoluminescence. These findings demonstrate the utility of the ligand moieties surrounding the gold frameworks for fine-tuning of the optical properties. During these studies, unusual but definite attractive interactions between the gold framework and C−H groups of the diphosphine ligand were found in the hexagold clusters. On the basis of careful crystallographic and NMR analyses, these interactions were deemed as a certain kind of M•••H hydrogen bonds, which critically affect the maintenance of the cluster framework. Such unique interaction activities are likely due to the valence electrons in the gold framework, which serve as the hydrogen-bond acceptor for the unfunc...