Hetero-biicosahedral [AuPd(PPh)(SCHPh)Cl] nanocluster: selective synthesis and optical and electrochemical properties.

A recent study implied that a hetero-biicosahedral 25-atom cluster composed of two kinds of icosahedral 13-atom clusters could serve as a molecular rectifier and dipole material. However, no hetero-biicosahedral 25-atom clusters containing three types of ligands, in this case, phosphines, halogens, and thiolates, have been reported. In this study, we selectively synthesized [Au24Pd(PPh3)10(SC2H4Ph)5Cl2]Cl (Au = gold, Pd = palladium, PPh3 = triphenylphosphine, SC2H4Ph = phenylethanethiolate, Cl = chloride), in which one Au was replaced with a Pd. The single-crystal X-ray structural analysis demonstrated that [Au24Pd(PPh3)10(SC2H4Ph)5Cl2]Cl was a hetero-biicosahedral 25-atom cluster in which the central atom of one icosahedral Au13 core was replaced by a Pd atom. Optical absorption spectroscopy suggested that the electronic structure of each individual icosahedral 13-atom core in [Au24Pd(PPh3)10(SC2H4Ph)5Cl2]+ was reasonably well maintained, similar to the case of [Au25(PPh3)10(SC2H4Ph)5Cl2]2+. Density functional theory calculation revealed that the peak splitting in the region below 2.2 eV of the optical absorption spectrum of [Au24Pd(PPh3)10(SC2H4Ph)5Cl2]+ is due to the splitting of HOMOs and also suggested that this cluster has dipole moment. Electrochemical measurements showed that [Au24Pd(PPh3)10(SC2H4Ph)5Cl2]+ was relatively stable to reduction. These results are expected to contribute to the development of molecular rectifiers and dipole materials based on hetero-biicosahedral 25-atom clusters.