Total Structure and Optical Properties of a Phosphine/Thiolate-Protected Au₂₄ Nanocluster

We report the synthesis and total structure determination of a Au24 nanocluster protected by mixed ligands of phosphine and thiolate. Single crystal X-ray crystallography and electrospray ionization mass spectrometry (ESI-MS) unequivocally determined the cluster formula to be [Au24­(PPh3)10­(SC2H4Ph)5­X2]+, where X = Cl and/or Br. The structure consists of two incomplete (i.e., one vertex missing) icosahedral Au12 units joined by five thiolate linkages. This structure shows interesting differences from the previously reported vertex-sharing biicosahedral [Au25­(PPh3)10­(SC2H4Ph)5­X2]2+ nanocluster protected by the same type and number of phosphine and thiolate ligands. The optical absorption spectrum of Au24 nanocluster was theoretically reproduced and interpreted.