X‑ray Crystal Structure and Theoretical Analysis of Au25–xAgx(SCH2CH2Ph)18– Alloy

The atomic arrangement of Au and Ag atoms in Au25–xAgx(SR)18 was determined by X-ray crystallography. Ag atoms were selectively incorporated in the 12 vertices of the icosahedral core. The central atom and the metal atoms in the six [−SR–Au–SR–Au–SR−] units were exclusively gold, with 100% Au occupancy. The composition of the crystals determined by X-ray crystallography was Au18.3Ag6.7(SCH2CH2Ph)18. This composition is in reasonable agreement with the composition Au18.8Ag6.2(SCH2CH2Ph)18 measured by electrospray mass spectrometry. The structure can be described in terms of shells as Au1@Au5.3Ag6.7@6×[−SR–Au–SR–Au–SR−]. Density functional theory calculations show that the electronic structure and optical absorption spectra are sensitive to the silver atom arrangement within the nanocluster.