Thiolate-induced structural reconstruction of gold clusters probed by 197Au Mossbauer spectroscopy

We investigated the structures of a series of glutathionate-protected gold clusters, Au-n(SG)(m) with n = 10-45, using Au-197 Mossbauer 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 [Au-25(SCH3)(18)](+) explains the Mossbauer spectra of Au-25(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.