Size-Focusing Synthetic Process and Properties of [Au25Cu8(S-Adam)19(PPh3)5]+ Nanocluster

Abstract

Compared with nanoparticles, nanoclusters have some unique properties, such as definite structure, surface effect, and quantum size effect. In this work, AuCu nanocluster protected by triphenylphosphine and adamantane mercaptan is synthesized and it is formulated to [Au₂₅Cu₈(S-Adam)₁₉(PPh₃)₅]⁺. With the characterization of UV-Vis absorption spectrum and Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF), the synthesis of [Au₂₅Cu₈(S-Adam)₁₉(PPh₃)₅]⁺ nanocluster is demonstrated to be a size-focusing process: polydisperse Au_mCu_n(S-Adam)_x(PPh₃)_y precursor with a size ranging from 900 Da to 2000 Da generates firstly and it transforms into [Au₂₅Cu₈(S-Adam)₁₉(PPh₃)₅]⁺ nanocluster in 3 days. TEM image demonstrates it is monodisperse distributing between 0.84 and 2.0 nm with an average size of 1.4 nm. TG shows a weight loss of 38.70% with ligands continuously breaking down between 200 and 330°C. Thermal stability test shows that it keeps well thermal stability at 40°C: the peaks of UV-Vis absorption spectrum gradually get weaken at 6 h and completely become a decaying curve at 8 h. This work provides a simple method to prepare AuCu nanocluster and affords new ideas for preparing Au-based alloy nanoclusters.