New method to dope gold nanoclusters by using metal surfaces of silver, copper and cadmium as sources of heteroatoms.

The fast metal exchange reaction between Au and AgAu nanoclusters in solution at -20 °C has been studied by in situ X-ray absorption spectroscopy (time resolved quick XAFS) in transmission mode. A cell was designed for this purpose consisting of a cooling system, remote injection and mixing devices. The capability of the set-up is demonstrated for second and minute time scale measurements of the metal exchange reaction upon mixing Au/toluene and AgAu/toluene solutions at both Ag K-edge and Au L-edge. It has been proposed that the exchange of gold and silver atoms between the clusters occurs via the SR(-M-SR) (n = 1, 2; M = Au, Ag) staple units in the surface of the reacting clusters during their collision. However, at no point during the reaction (before, during, after) evidence is found for cationic silver atoms within the staples. This means that either the exchange occurs directly between the cores of the involved clusters or the residence time of the silver atoms in the staples is very short in a mechanism involving the metal exchange within the staples.

A CuAu bimetallic nanocluster was synthesized by adding a single copper atom to the Au(2-PET) nanocluster. The absence of CuAu(2-PET) doped species was demonstrated by MALDI-TOF mass spectrometry. A separation of bimetallic clusters was attained for the first time where isomers of the E2 enantiomer of the AuCu(2-PET) adduct were successfully isolated from their parent cluster using chiral HPLC. The CD of the isolated isomers revealed a change in their electronic structure upon copper addition. The luminescence of the AuCu adduct is significantly enhanced in comparison with the parent Au nanocluster. The stability of the newly formed adduct is strongly dependent on the coexistence of the Au nanoclusters.