Engineering magic number Au₁₉ and Au₂₀ cage structures using electron withdrawing atoms.

Area of Science:

• Computational Chemistry
• Materials Science
• Nanotechnology

Background:

• Gold cages, a type of gold nanoparticle, possess favorable physicochemical properties.
• Chemical stability is crucial for the practical application of gold cage structures.
• Transforming non-magic number cages into magic number cages enhances stability.

Purpose of the Study:

• To investigate the electronic properties of gold cages (Au19X and Au20X2, where X = F, Cl, Br, I).
• To enhance the chemical stability of gold cages by introducing electron-withdrawing groups.
• To determine if halogen substitution can convert non-magic number gold cages into magic number structures.

Main Methods:

• Computational optimization of initial gold cage geometries to verify local minima.
• Attachment of halogen atoms (F, Cl, Br, I) to gold cages.
• Calculation of Nuclear Independent Chemical Shift (NICS) values and Highest Occupied Molecular Orbital-Lowest Unoccupied Molecular Orbital (HOMO-LUMO) gaps.

Main Results:

• More electronegative halogens resulted in more negative NICS values, indicating increased aromaticity.
• Au19F and Au20F2 exhibited the most negative NICS values, signifying enhanced spherical aromaticity.
• Iodine substitution led to the most positive NICS value and the smallest HOMO-LUMO gap.

Conclusions:

• Electron-withdrawing halogen groups can positively charge gold cages, enhancing their stability.
• Fluorine substitution is most effective in achieving magic number gold cage structures with high aromaticity.
• The study provides insights into tuning the electronic properties and stability of gold nanoparticles.