Study of the structure and electronic state of thiolate-protected gold clusters by means of 197Au Mössbauer spectroscopy

Abstract

We have investigated the structures and electronic states of a series of glutathionate-protected Au clusters, Au n (SG) m with n = 10 − ∼55, using 197 Au Mössbauer spectroscopy, which allows us to probe the local environment of the constituent Au atoms via isomer shift (IS) and quadrupole splitting (QS). The spectral profile abruptly changes on going from Au 22 (SG) 17 to Au 25 (SG) 18 , then it smoothly changes to that of Au∼ 55 (SG) m . However, the spectral profile dramatically changes on going from Au∼ 55 (SG) m to the dodecanethiolate-protected Au cluster with average diameter of 2 nm. The 197 Au Mössbauer spectra of glutathionateprotected Au clusters and dodecanethiolate-protected Au clusters were successfully analyzed on the basis of the structure and electronic state of Au 25 (SG) 18 .

Fine structure of gold nanoparticles stabilized by buthyldithiol: Species identified by Mössbauer spectroscopy

“…The third component can be assigned to surface gold [29] in good correspondence with the quadrupole splitting values shown in Table 1. The fourth component can probably be originated from the middle of the mentioned bridging "staples", namely from gold atoms removed from the metallic surface and located in between two sulphurs, in good correspondence with data reported earlier for this S Au(I) S component [3,4,21,23,29]. It is worth noticing that the fraction of the surface components extracted from the relative intensity values shown in Table 1 is 53%.…”

“…The second component can probably be assigned to a surface bare metallic component. Evolution of a surface component with quadrupole splitting in 1.7-3.5 mm/s range in dependence of decrease of particles size is reported in [29]. Analogously, the component with 2.02 mm/s quadrupole doublet may be attributed to these bare surface gold atoms.…”

“…A particular advantage is that oxidation state of gold can also be derived from spectra [28]. Glutathione encapsulated various Au m (10 < m < 45) molecular clusters have already been characterized by the method, existence of different types of Au S bonds were revealed [21,29]. Studies were also performed starting from the other, metallic side of the transition region.…”

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles

“…Several other spectroscopic techniques such as magnetic circular dichroism (MCD), − electron paramagnetic resonance (EPR), − extended X-ray absorption fine structure (EXAFS), − Mössbauer, − X-ray diffraction (XRD), magnetophotoluminescence spectroscopy, etc., have also been used for detailed understanding of the structure of atomically precise gold clusters, and a comprehensive list can be found in Table S1. A recent example of the power of EXAFS was shown by Yamazoe et al, where hierarchy in the bond stiffness in clusters such as Au 25 (PET) 18 , Au 38 (PET) 24 , and Au 144 (PET) 60 has been measured successfully.…”