The solely motif-doped Au36−xAgx(SPh-tBu)24 (x = 1–8) nanoclusters: X-ray crystal structure and optical properties

Abstract

We report the observation of new doping behavior in Au_36−xAg_x(SR)₂₄ nanoclusters (NCs) with x = 1 to 8. The atomic arrangements of Au and Ag atoms are determined by X-ray crystallography. The new gold–silver bimetallic NCs share the same framework as that of the homogold counterpart, i.e. possessing an fcc-type Au₂₈ kernel, four dimeric AuAg(SR)₃ staple motifs and twelve simple bridging SR ligands. Interestingly, all the Ag dopants in the Au_36−xAg_x(SR)₂₄ NCs are selectively incorporated into the surface motifs, which is in contrast to the previously reported Au–Ag alloy structures with the Ag dopants preferentially displacing the core gold atoms. This distinct doping behavior implies that the previous assignments of an fcc Au₂₈ core with four dimers and 12 bridging thiolates for Au₃₆(SR)₂₄ are more justified than other assignments of core vs. surface motifs. The UV-Vis adsorption spectrum of Au_36−xAg_x(SR)₂₄ is almost the same as that of Au₃₆(SR)₂₄, indicating that the Ag dopants in the motifs do not change the optical properties. The similar UV-Vis spectra are further confirmed by TD-DFT calculations. DFT also reveals that the energies of the HOMO and LUMO of the motif-doped AuAg alloy NC are comparable to those of the homogold Au₃₆ NC, indicating that the electronic structure is not disturbed by the motif Ag dopants. Overall, this study reveals a new silver-doping mode in alloy NCs.