Synthesis,Structure And Properties Of Cu,Ag Nanoclusters Protected By Zwitterionic Ligands

As a new class of nanomaterials,coinage metal nanoclusters protected by organic ligands(such as alkynyl,thiolate,and phosphine,etc.)have been extensively studied.Due to the quantum size effect of clusters,they exhibit physical and chemical properties that are significantly different from those of bulk materials,among which photoluminescence is one of the most attractive properties of d10 metal nanoclusters,which have been applied in sensing,biomedicine and other fields.Controlling the synthesis and structure of nanomaterials at the atomic level is the basis for exploring their practical applications.Ligand engineering is one of the effective strategies to control the structure of nanoclusters.A class of has been widely used in metal nanoclusters.The molecule of zwitterionic ligand has both cationic and anionic groups,and has an electric dipole moment.The formed charge layer can effectively passivate the surface of metal nanoclusters,which is important for the self-assembly process of the clusters.In addition,experimental studies have shown that ligands with large steric hinderance will lead to unsaturated coordination of some metal atoms on the surface of the nanoclusters,while small auxiliary ligands can occupy the vacancies to stabilize metal nanoclusters.It is feasible to introduce small sterically hindered ligands(such as-Cl,-Br,-I)to prepare metal nanoclusters with diverse structures.In this thesis,we used large sterically hindered sulfur-containing zwitterionic ligands and different kinds of halide anions to construct several silver and copper nanoclusters.Based on this,our work is divided into the following two parts:First,three copper nanoclusters co-protected by large sterically hindered sulfurcontaining zwitterionic ligands(NaL·Br=NaS(CH2)3(C6H5)3PBr)and halogen anions(Cl-,Br-,and I-),[Cu14L6Br12C12](1),[Cu16.5L6Br16.5]n(2)and[Cr15L6Br2I12S](3),were successfully prepared by one-pot reduction method,and characterized by singlecrystal X-ray diffraction analysis and X-ray energy dispersive spectroscopy(EDS)analysis.Compounds 1-3 all have a three-layer parallel arrangement of "Cu3-Cu6Cu3".Interestingly,compound 2 contains two one-dimensional cluster-based chains extending in different directions and adopting different Cu14L6Br14(I)and Cu16L6Br16(Ⅱ)buiding units.Compounds 1-3 exhibit a reversible thermochromic luminescence upon UV irradiation,and the luminescence spectra reveal the maxum emissions of 1:λem=619 nm,2:λem=567 nm,3:λem=576 nm at room temperature,and 1:λem=608 nm,2:λem=546 nm,3:Aem=536 nm at 80 K.This work provides a reference for the preparation of metal nanoclusters from large organic ligands,and also shows that halides are crucial for the construction of metal nanoclusters.Second,we successfully prepared a series of silver nanoclusters,[Ag18L12Br12]Br6(4),[Ag33L20Br18](Ph4B)4(5)and[Ag23L12(CF3CO2)15](SbF6)4(6),with NaL-Br and different kinds of silver salts by optimizing the experimental conditions(such as introducing bisphosphine ligands and replacing anions)to control the self-assembly process of metal nanoclusters.The precise structures of compounds 4-6 were successfully determined by single-crystal X-ray diffraction analysis.Compound 4 was composed of five parallel and closed six-membered rings connected to form a column-like structure;compound 5 has a perfect "bipyramid" Ag11 core protected by a Ag12S12Br8 shell,and the upper and lower ends are connected with a twisted tetrahedron Ag6S4Br4 to form an "S-type" overall structure;the metal frame of compound 6 can be regarded as a twisted truncated tetrahedron structure.Compound 4 is non-emissive,while compound 5 exhibits bright red triplet phosphorescence emission(λem=681 nm)in the solid state with a microsecond-scale lifetime(τ=36.51 μs)and a large Stokes shift(Δ≈182 nm).Compound 6 only exhibits red photoluminescence(λem=670 nm)at low temperature of 80 K.