Crystal Structure of AuAg(S-Bu) and Effect of the Ligand on Ag Alloying in Gold Nanomolecules.

We report the X-ray crystal structure of the AuAg(S-Bu) alloy and the effect of the ligand on alloying site preferences. Gold-silver nanoalloys prepared by co-reduction of metal salts are known to have only partial Ag occupancies. Interestingly, AuAg(S-Bu) has on the surface, capping, and staples sites. The AuAg(S-Bu) ( = 1-5) composition was confirmed by X-ray diffraction and electrospray ionization mass spectrometry studies. Thiolate ligands can be categorized into three classes on the basis of the groups at the α-position as aliphatic, aromatic, and bulky thiols. The effect of the ligand on Ag doping can be clearly seen in the crystal structures of AuAg(SPh-Bu) and AuAg(SCHCHPh) when compared with that of AuAg(S-Bu). Ag is preferentially doped onto the core surface when the ligand is aliphatic, and Ag is doped in both core surface and staple metal sites when the ligand is aromatic or bulky.