Syntheses, Properties And Au Doping Of Tiara-like Thiolated Palladium Nanoclusters

Thiolated metal nanoclusters with tiara-like structure ([M(SR)2]n, M denotes Ni, Pd, Pt) currently consititutes one new hot topic in the nanoscience and nanotechnology research. Owning to the uniform tiara structure and continuous tunability of metal atom number n, [M(SR)2]n nanoclusters serve as ideal materials for systematically investigating the n-properties correlation. The provious study of [M(SR)2]n focuses on the [Ni(SR)2]n nanoclusters, however, the various ligands and limited values of n in [Ni(SR)2]n nanoclusters impede the systematical investigation on the relationship between structure, properties and metal atom number. In this work, we have successfully synthesized a series of tiara-like [Pd(SR)2]n nanoclusters with same ligand but continuously changed values of n, and doped Au atom(s) into [Pd(SR)2]4 and [Pd(SR)2]s. The relations between the optical absorption (electrochemical properties or HOMO-LUMO gap) and the palladium atom number, the doping law of Au into tiara-like [Pd(SR)2]n, and the evolution of optical properties, electrochemical properties, HOMO-LUMO gap with Au doping have also be studied systematically.The main points of this work are shown as follows:1. A modified strategy (reacting M(II) salt with phenylethanethiol under weak alkaline condition at room temperature) has been applied to facilely prepare a series of tiara-like [M(SR)2]n nanoclusters in one-pot; preparative thin lay chromatography (PTLC) was introduced to isolated a family of [Pd(SC2H4Ph)2]n (4≤n≤20) nanoclusters, all of which have been successfully characterized by matrix-asisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) after adding Na+ to assist the ionization of palladium nanoclsuters. Their tiara structures were determined by single crystal X-ray crystallography together with theoretical calculation; their formation mechanism was proposed to be substitution-polycondensation-ring closure process supported by experimental evidences. All of these clusters are rather robust (anti-reductive, anti-oxidative, heat-resistant and long-term ambient-stable) owing to their special tiara-like structures. The optical absorption and electrochemical properties evolves with the increase of n value, and a turning point occurs when the value of n reaches 8. The HOMO-LUMO gaps enlarge with the size increase when the value of n in [Pd(SR)2]n nanoclusters is less than 8, while it keep almost unchanged after the value of n is larger than 8.2. Doping Au into tiara-like [Pd(SC2H4Ph)2]n nanoclusters. Three thiolated Au-Pd alloy clusters (Au2Pd3(SC2H4Ph)8, Au4Pd2(SC2H4Ph)8, Au2Pd4(SC2H4Ph)10) have been successfully synthesized by reacting the mixed Au(Ⅲ) and Pd(Ⅱ) salts with HSC2H4Ph under weak alkaline condition, isolated by PTLC, identified by MALDI-TOF-MS, and structurally resolved by single crystal X-ray crystallography together with theoretical calculation. It is revealed that two Au atoms substitute a Pd atom without changing the tiara-like structure during Au doping of [Pd(SR)2]n nanoclusters. With the content of Au increases, the optical absorption and electrochemical properties of Au doped palladium nanoclusters evolve regularly, especially, both the optical and electrochemical gaps enlarge, which retionally interpreted by theoretical calculation. It is worth noting that Au4Pd2(SC2H4Ph)8 nanocluster bears chirality originating from the opposity twist of Au4Pd2S8 framework and thiolate ligands, and Au4Pd2(SC2H4Ph)8 nanocluster is the smallest chiral cluster thus far to our best knowledge.In the end, a summary of this work and a prospect for further work are presented.