B₄-engine as the rotational driver of the B₁₃⁺ cluster: study based on BOMD analysis

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Boron clusters exhibit significant fluxionality and aromaticity.
• The B4 unit dynamically interconverts between square (TS, D4h) and diamond (GS, D2h) configurations.
• This B4 dynamic is crucial in the B13+ molecular rotor, driving outer ring rotation.

Purpose of the Study:

• To establish a dynamic correlation between isolated B4 clusters and B4 units within B13+ clusters.
• To investigate the role of B4 dynamics in the B13+ molecular rotor's collective rotational behavior.
• To analyze the transformation mechanisms governing the B13+ cluster's stepwise rotation.

Main Methods:

• Density Functional Theory (DFT) calculations using PBE1PBE/6-311+G(d).
• Born-Oppenheimer Molecular Dynamics (BOMD) simulations at 150 K for 5000 fs.
• Adaptive Natural Density Partitioning (AdNDP) analysis to study bonding evolution.

Main Results:

• Observed recurring diamond-square-diamond (DSD) to diamond-diamond (DD) transformations in B4 units.
• These transformations govern the stepwise rotation of the B13+ cluster.
• Timescale and bonding analyses revealed a direct correspondence between isolated B4 and embedded B4 dynamics.

Conclusions:

• The intrinsic dynamics of the B4 cluster are fundamental to the B13+ molecular rotor's function.
• The B4 unit's fluxionality orchestrates the collective rotational motion within the B13+ rotor.
• This study provides insight into the structure-dynamics relationship in complex boron clusters.