A ternary Li₃B₇Si₃ cluster: when reduced electron delocalization enhances thermodynamic stability

Area of Science:

• Computational Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Investigating the stability and electronic properties of boron-silicon clusters is crucial for understanding novel materials.
• The B7Si3 cluster exhibits interesting electronic structures, but its planar triangular isomer (T+) is thermodynamically unstable despite double aromaticity.

Purpose of the Study:

• To investigate the stability and electronic structure of B7Si3(q) (q = +, 0, -, 2-, 3-), Li3B7Si3, and Li3B10H3 clusters.
• To explore strategies for stabilizing the planar triangular form of B7Si3+.
• To elucidate the electronic origins of stabilization in these boron-silicon systems.

Main Methods:

• Comprehensive isomer search to identify stable cluster structures.
• Theoretical calculations including ring current maps, Atoms in Molecules (AIM) analysis, Electron Localization Function (ELFσ), and Natural Orbitals for Chemical Valence (ETS-NOCV).
• Analysis of electronic structure, aromaticity, and bonding characteristics.

Main Results:

• The planar triangular T+ isomer of B7Si3+ is thermodynamically unstable.
• Sequential addition of up to four electrons stabilizes the cluster, with T2- being the most favorable charged isomer.
• Incorporation of lithium atoms leads to a significantly more stable star-shaped Li3B7Si3 cluster, which exhibits a balanced sigma-pi aromatic character.

Conclusions:

• Stabilization of the triangular B7Si3 cluster can be achieved by electron addition or lithium incorporation.
• The Li3B7Si3 cluster displays enhanced stability due to a shift towards a benzene-like sigma-pi aromatic system.
• Peripheral sigma delocalization plays a critical role in stabilizing planar aromatic clusters.