Full Protection of Intensely Luminescent Gold(I)-Silver(I) Cluster by Phosphine Ligands and Inorganic Anions

Abstract

An intensely luminescent gold(I)-silver(I) cluster [(C)(AuPPhpy₂ )₆ Ag₆ (CF₃ CO₂ )₃ ](BF₄ )₅ (PPhpy₂ =bis(2-pyridyl)phenylphosphine) (3) is synthesized by the reaction of [(C)(AuPPhpy₂ )₆ Ag₄ ](BF₄ )₆ with AgCF₃ CO₂ . All eight faces of the octahedral C@Au₆ core in 3 are capped, that is, six faces are capped by silver ions and two by tetrafluoroborates. Cluster 3 is intensely luminescent in solution with a quantum yield of 92 %. Ligation of CF₃ CO₂^- ions is vital for the construction and emission properties of 3, as confirmed by DFT calculations. BF₄^- ions are involved in the protecting sphere of the metal core, as evidenced by ¹⁹ F NMR data. The participation of phosphines, CF₃ CO₂^- , and BF₄^- ions in the protection of the emissive core and the enhancement of the rigidity of the cluster result in the high emission efficiency. This is the first example of organic ligands and inorganic anions forming a rigid protecting sphere for luminescent coinage-metal clusters.

Keywords: anions; cluster compounds; gold; luminescence; silver.