Derivatives of the thiolate-protected gold cluster Au-25(SR)(18)(-1)

Loss of small fragments (like AuL, Au2L3, Au4L4) have been found systematically in several MALDI and FAB experiments on thiolate-protected gold clusters of different sizes. When using the cluster Au25L18 (-1) as parent cluster, the fragmented cluster Au21L14 (-1) has been reported to be obtained in high proportion (L = SCH2CH2Ph). Here we analyse a few possible fragmentation patterns of the well-known parent cluster Au25L18 (-1) (L = SCH3). Using DFT calculations we study the different atomic configurations obtained after a AuL fragment is lost from Au25L18 (-1). We found energetically favourable configurations that can be written as Au-13 [Au2L3](6-z) [AuL2] (z) (-1), where the modification can be described as a replacement of the long protecting unit by a short one (Au2L3 -> AuL2). A full replacement (z = 6) gives rise to a protected Au19L12 (-1) cluster. This mechanism does not modify the super-atomic electronic structure of the gold core, i.e., all these fragments remain an 8 electron super-atom clusters exactly like the parent Au25L18 (-1). We suggest that the Au19L12 (-1) cluster could be realized by using a bulky thiolate, such as the tert-butyl thiolate SC(CH3)(3) .