Syntheses and Characterization of Coin Metal Clusters Protected by Alkynyl And/or Phosphine

Author:Qu Mei

Supervisor:zhang xian ming li huan


Degree Year:2019





In the past few decades,great progress has been made in the synthesis,structural determination and performance studies of coinage metal nanoclusters.Monodisperse colloidal nanoclusters with well-defined molecular structure,which is very beneficial to investigate the correlation between their structure and properties,has caused great concern.Colloidal metal nanoclusters are mostly macromolecules composed of many components,so how to prepare and characterize nanoclusters is a huge challenge for scientists.It has been found that properties can be optimized by controlling the geometry and electronic structureds of the nanoclusters.A metal nanocluster usually consists of a metal core and peripheral ligands.The ligands are usually used as a stabilizer,and in many cases,they can affect the formation of nanoclusters,and even determine the size,shape and properties of the nanoclusters.Commonly used ligands include thiols,phosphines,halides,etc.In recent years,alkynyl ligands have been increasingly used for the synthesis of coinage metal nanoclusters due to their versatile coordination modes.In this paper,a series of silver and copper nanoclusters were synthesized using alkynyl and/or phosphine ligands.The main contents are divided into the following points:(1)The first all-alkynyl-protected [Ag74(C≡CPh)44](NO3)2 nanocluster was synthesized by using a bidentate phosphine ligand as an auxiliary ligand.The crystal structure was characterized by single-crystal X-ray diffraction.It was found that the core of Ag74 is arranged in a Ag4@Ag22@Ag48 three shell structure,and all phenylacetylenes coordinated with Ag in a μ3 mode.31P NMR results showed that dppp firstly combined with Ag atoms to form a dinuclear complex,and after the reduction,the Ag atoms were released to the phenylethynyl ligands.On this basis,the influence of the steric hindrance effect of the substituents at different positions on the cluster structure was also investigated,and two other [Ag74(2-MePhC≡C)44](NO3)2 and [Ag74(3-Me Ph C≡C)44](NO3)2 nanoclusters were synthesized.Mass spectrometry and single crystal analysis indicate that their cores are the same as Ag74.Both are Ag4@Ag22@Ag48 core-shell structures,each containing (44) alkynyl ligands,and charge number of the skeletons are +2.In addition,an alkynyl-phosphine co-protected Ag33(4-MePhC≡C)22(dppp)4 nanocluster was synthesized,and its structure and optical properties are studied,the Ag atoms are arranged in a Ag3@Ag20@Ag10 three shell structure.(2)We have successfully synthesized three alkynyl-phosphine co-protected Cu53 nanoclusters containing Cu(0),including Cu53(C≡CPhPh)9(dppp)6Cl3(NO3)9,Cu53(C≡CPh)9(dppp)6Cl3(NO3)9 and Cu53(4-FPh C≡C)9(dppp)6Cl6-(OAc)6,and the synthesis process,structure and properties were characterized in detail.X-ray single crystal analysis show that the 41 Cu atoms in the core of Cu53 are layered in an unusual mixed FCC and HCP stacking sequence(ABABC),while the bulk metallic copper usually featured FCC stack,giving strong evidence that Cu atoms can be arranged in non-FCC lattice at ambient condition when confined by proper ligands.To our knowledge,Cu53 is also the copper nanoclusters with the most Cu(0)so far.And characterization methods including XPS,X-ray absorption,ESI-MS,IR and UV-visible spectroscopy etc.have been carried out.It is revealed that CuⅡ first turned into CuⅠ when coordinated with phosphine.The following addition of Na BH4 and aging step further reduced it to Cu53.The effects of different electron withdrawing groups on the structure and catalytic properties of the clusters were also investigated.(3)A top-down approach has been developed to synthesize three novel alkynyl and phosphine protected Cu(Ⅰ)clusters whose structure and properties are well defined,including Cu4dppp3(PhC≡C)3](NO3)2 with a rare centered triangular planar configuration,a trigonal prism type [Cu6dppe3(PhC≡C)5]NO3,and a zigzag Cu4dpph2(PhC≡C)4.Mechanism study indicated Cu nanoparticles were gradually oxidized at ambient condition to give CuO and Cu2O as precipitate and Cu cluster was crystallized from the supernatant.In addition,the two planar Cu4 clusters,especially Cu4dppp3(PhC≡C)3](NO3)2,indicate outstanding luminescent properties,the quantum yield is as high as 69.84%.