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    Home > Angelw: derivative ligands regulate the electronic structure of gold nanoclusters

    Angelw: derivative ligands regulate the electronic structure of gold nanoclusters

    • Last Update: 2019-09-03
    • Source: Internet
    • Author: User
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    Gold nanoparticles have been widely used in photocatalysts, photovoltaic devices, chemical sensors and nonlinear optical media due to their atomic accuracy

    Electronic structure has a great influence on the properties and reactivity of nanoparticles

    However, up to now, there is no clear boundary between the geometric structure and electronic structure of nanoclusters, especially the particle environment interface

    The framework of electronic properties of nanoparticles can be achieved by chemical derivatization and precise measurement, but its surface chemistry is difficult to explore due to the need for precise synthesis and separation methods

    Anisotropic solvent environment, thermal average, dissociation of impurities from ligands or core isomerization affect the quantitative comparison of substances and hinder the development of electronic structure rationalization framework

    In order to overcome these challenges, Professor Christopher J

    Johnson of Stony Brook University in the United States designed a fine electronic structure probe by using the low-temperature ion trap Photofragmentation spectrum, a measurement method combining mass spectrometry with low-temperature UV Vis Spectrum

    Based on the standard wet synthesis method, a group of gold nanoclusters with different size and ligand composition were reported (Au 8 (PPh 3) 2+ 7 and Au 9 (PPh 3) 3+ 8), and were verified by electrospray ionization mass spectrometry

    Relevant achievements were published on angel

    Chem

    Int

    ed

    (DOI: 10.1002 / anie

    201907586) under the title of "systematically tuning the electronic structure of gold nanocluster through living derivation"

    Firstly, the crystal structure of Au 8 (PPH 3) 2 + 7 and Au 9 (PPH 3) 3 + 8 is analyzed

    It is found that the metal nuclei of Au 9 (PPH 3) 3 + 8 and Au 8 (PPH 3) 2 + 7 are d 2H symmetrical (Figure 1a), which shows that the two clusters are related by cutting a single Au (I) PPH 3 unit

    Then, the UV Vis spectra of the same reaction mixture were compared with that of the mass separation cluster

    The UV Vis spectra show five distinct transitions, with the centers at 291, 316, 344, 416 and 479 nm, respectively

    In the Photofragmentation spectrum, there are 14 bands in each cluster, and there are key transitions in the lowest energy region, including the band centered at 505 nm for Au 9 (PPH 3) 3 + 8 and the band centered at 601 nm (Figure 1b)

    At short wavelengths, there is a close correspondence between the main features of the two spectra, which shows that although their compositions are different, they have striking similarities in electronic structure

    (source: angelw

    Chem

    Int

    ed.) next, the author compared the spectra in Figure 1 in EV

    The broken line of figure 2A shows the electronic transition between Au 8 (PPH 3) 2 + 7 and Au 9 (PPH 3) 3 + 8

    The four lowest energy transitions between 2.0 and 2.8 EV may be produced under the dominant state of delocalized gold

    The transition between 2.8 EV and 4.4 EV is mainly caused by the transition of electrons from the metal core orbit to the orbit on the ligand (metal ligand charge transfer (MLCT) band)

    The Hammett constants (σ P) of triphenylphosphine, tris (4-methylphenyl) phosphine and tris (4-methoxyphenyl) phosphine linked Au 8 (PPH 3) 2 + 7 and Au 9 (PPH 3) 3 + 8 nanoclusters are compared

    It is found that the electron strength of the substituent is - H < - me < - ome (Figure 2a-c)

    At the same time, with the increase of the electron strength, the energy of the ligand appears a red shift (Figure 2D)

    In addition, there is a good linear correlation between the peak centers of the two nanoclusters and σ P (Figure 2e)

    The results show that the electronic structure of nanoclusters can be controlled systematically and quantitatively by the electronic properties of ligands

    The analysis of different substituent crystal structures in Figure 2F further verifies that it is electrons rather than geometry that cause the red shift

    (source: angelw

    Chem

    Int

    ed.) in order to find out whether there is a weaker binding substance that can be used as a probe for the electronic structure of the interface, the author measured the spectrum of N 2 instead of he as a mass action marker of triphenylphosphine protected cluster (Figure 3)

    The response of the two spectra is the characteristics of the probe

    The maximum value of the peak has a change of up to 50 MeV, which shows that the electronic structure of the probe is similar

    The dominant trend of the low energy peak is blue shift after the introduction of N2, which shows that the adsorption of N2 significantly reduces the charge density on the metal core

    The larger offsets of Au 8 (PPH 3) 2 + 7 and Au 9 (PPH 3) 3 + 8 occur in the range of 2.50-2.80 EV, indicating that at least one orbit involved in these two transitions shows significant interface characteristics

    (source: angelw

    Chem

    Int

    ed.) in a word, the author found that ligands can not only stabilize the metal core, but also have some influence on the electronic structure, even on the orbit with small direct probability density on the ligands

    Ligand chemistry affects the electronic structure of nanoclusters with similar size and symmetry

    In addition, solvent and interface effects can be used to fine tune the specific electronic structure, especially for the directly involved interface process of nanoclusters

    This hierarchical structure has formed a preliminary framework, which can be used for reference in the reasonable design of nanoclusters, and can be extended to space effect, ligand binding group effect and alloy composition

     
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