Thiolate-Induced Structural Reconstruction of Gold Clusters Probed by ¹⁹⁷Au Mössbauer Spectroscopy

Abstract

We investigated the structures of a series of glutathionate-protected gold clusters, Au n (SG) m with n = 10−45, using 197Au Mössbauer spectroscopy, which allows us to probe the local environment of the Au sites via isomer shift (IS) and quadrupole splitting (QS). The spectral analysis, with the help of recent theoretical results on methanethiolated gold clusters, revealed that Au−SG oligomeric rings are preferentially formed around the Au core. Specifically, a core-in-cage structural motif theoretically predicted for [Au25(SCH3)18]+ explains the Mössbauer spectra of Au25(SG)18 fairly well and thereby explains the high stability against the core-etching reaction. The positive IS and QS values for the Au cores of Au n (SG) m suggest a nontrivial effect of thiolate ligation on the electronic structure of the underlying gold clusters.

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

“…Among small Au clusters, the Au-thiolate compound composed of 25 Au atoms and 18 thiolates (Au 25 (SR) 18 ) has been studied most extensively as a prototype system of stable Au n (SR) m clusters [3]. In 2007, we proposed the structure of Au 25 (SG) 18 by 197 Au Mössbauer spectroscopy [4], based on the "core-in-cage" model theoretically predicted by Iwasa and Nobusada; the Au 7 core is caged by two -[Au-S(R)-] 3 and one -[Au-S(R)-] 12 cyclic oligomers [5]. Since then, the geometrical structure of Au 25 (SC 2 H 4 Ph) 18 was determined by single crystal X ray diffraction [6] and by theoretical calculation [7].…”

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

“…Appearance of an intense band at 285 cm −1 clearly attests for the presence of Au S bonds in good correspondence with [4]. Other characteristic bands also appear, namely symmetrical skeleton vibration at 1035 cm −1 , bending and valence vibrations for CH 2 at 1452 and 2926-2853 cm −1 , respectively. It is worth mentioning that the band for free SH is missing from the spectrum (it should appear at 2550-2600 cm −1 ).…”

“…Beside the Au S linear bonds additional monomeric (Au metal -SRAu(I)-SR-Au metal ) and dimeric (Au metal -SR-Au(I)-SR-Au(I)-SRAu metal ) "staples" can be formed in large molecular complexes, containing only a few dozens of core gold atoms. These structures are dominant at small thiolate encapped Au m (10 < m < 45) molecular clusters [2,4,21,22] and they can be observed on the sur face of larger particles as well [3,23]. On well-developed crystal faces of larger particles thiol molecules may form self-assembled monolayers [24].…”

“…In the low size range there are certain x values for Au x clusters at which their stabilization is preferred (25, 38, 55, 144, etc. ) [2][3][4][5]. Transition from these large molecular complexes (exhibiting separate valence bands) to metallic particles is around at Au 55 , i.e.…”

DFT calculations for the heterojunction effect between metal clusters and the stabilizer molecules

“…However, the metal clusters are missing the surface active metal atoms as the strong covalent bond between the surface metal atoms in cluster and S atom in the stabilizer is generated in case of metal clusters stabilized with thiol group [19,20]. On the other hand, the surface-exposed Pd atoms in Pd clusters are covered only partly with amine groups in PPI and the number of the connection points between Pd cluster and amino groups in PPI is limited, as PPI has only one amino group in one propylene imine molecule unit in the dendrimer structure, as shown in Figure 1(a).…”