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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)18x with a distribution of charge states, which shifts toward negative values with reduction time. The stable ions Au25(SC6H13)181+ and Au25(SC6H13)181- can be synthesized by chemical oxidation and reduction of Au25(SC6H13)180, respectively. These findings lead us to conclude that electronic shell closing is not a crucial factor for the high stability of Au25(SC6H13)18x (x = 1−, 0, 1+). We ascribe magic stability to the core-in-cage structure predicted theoretically.
Negishi et al. (2007) studied this question.