Orbital Localization-Driven Disruption of Peripheral Bonding in Valence-Isoelectronic B₁₂^- Clusters

Area of Science:

• Computational Chemistry
• Materials Science
• Quantum Chemistry

Background:

• The B₁₂^- cluster serves as a foundational model for studying electronic structure and bonding.
• Understanding the impact of substituting boron with heavier Group 13 elements is crucial for designing novel materials.
• Valence-isoelectronic substitutions offer a pathway to tune cluster properties while maintaining electron counts.

Purpose of the Study:

• To systematically investigate the geometric and electronic structural changes in B₁₂^- upon substitution with Al, Ga, and In.
• To determine the stability of various substituted cluster compositions (e.g., AlB₁₁^-, Ga₂B₁₀^-, AlGaB₁₀^-, Al₃B₉^-).
• To elucidate the bonding mechanisms and electron localization effects induced by these heavier dopants.

Main Methods:

• Global minimum structure searches were performed using the Coalescence Kick (CK) algorithm across different spin states.
• High-level electronic structure calculations (DLPNO-CCSD(T)/aug-cc-pVTZ//U-TPSSh-D4/def2-TZVPD) were employed for energy evaluations.
• Adaptive Natural Density Partitioning (AdNDP) analysis was used to characterize bonding and electron distribution.

Main Results:

• The B₁₂^- motif is preserved in clusters with up to two substitutions (Al₂B₁₀^-, Ga₂B₁₀^-) and mixed-metal compositions (AlGaB₁₀^-).
• Dopant substitution leads to the localization of unpaired electrons into s-type orbitals on dopant atoms, replacing delocalized π-bonding and causing geometric puckering.
• Extensive substitution (Al₃B₉^-) or the incorporation of heavier elements like Indium (InB₁₁^-, GaInB₁₀^-) breaks the valence-isoelectronic principle, leading to structural distortions and 3D structures due to lone-pair formation.

Conclusions:

• The study demonstrates that the quasi-planar B₁₂^- core can accommodate lighter Group 13 dopants while maintaining its structural integrity.
• Electron localization effects, particularly the formation of s-type lone pairs on heavier dopants, significantly influence cluster geometry and stability.
• The findings provide insights into the limits of the valence-isoelectronic principle in substituted boron clusters and guide the design of new materials with tailored electronic properties.