The Au25(SR)18 cluster carrying icosahedral dodecaborate and glutathione ligands: A spectroscopic view

The functionality of Au-25(S-glutathione)(18) clusters change when some of the ligands in the cluster shell are replaced for other species. In this study we report on the synthesis and characterisation of a new cluster in which undecahydro-closo-dodecaborate thiolates are introduced as constituents of the shell surrounding the gold core. This is the first reported example in which the Au-13 core of the Au-25(S-glutathione)(18) cluster is covered with an Au-S-B linkage instead of an Au-S-C on the dimeric shell units using a ligand exchange reaction. The spectra of the new cluster species clearly indicate a successful ligand exchange while retaining the gold core with undisrupted semirings containing both thiolate species. The resulting clusters were identified as Au-25 [(S-glutathione)(18-x) (S-closo-borate)(x)(-))] (x = 3, 4). Despite the achiral character of the closo-borate thiolates entering the semiring, increased chirality traces were observed in the high-energy region. Circular dichroism (CD) responses are ligand dependent and provide a fingerprint characteristic of the ligands present in the cluster. The next generation of such surface functionalized clusters provides unique base for computational and application studies.

Automated summary

The synthesis and characterisation of a new Au-25 cluster with Au-S-B linkages in the shell surrounding the gold core is reported in this study. The successful ligand exchange in the new cluster was indicated by the spectra while maintaining the gold core and semirings containing two thiolate species. This surface functionalized cluster provides a unique base for computational and application studies.