The effects of halogen elements on the opening of an icosahedral B12 framework

TL;DR

This study uses density functional theory to explore how different halogen atoms influence the structural stability and IR spectra of B12 clusters, revealing that heavier halogens increase the energy barrier for cage opening.

Contribution

It provides new insights into the effects of various halogen substitutions on B12 cluster stability and IR spectral shifts, expanding understanding of cluster chemistry.

Findings

Halogen elements do not significantly alter cluster geometries.

IR spectra show a blue-shift with heavier halogens.

Heavier halogens increase Gibbs free energy differences between open and closed structures.

Abstract

The fully halogenated or hydrogenated B12X12 (X = H, F, Cl, Br and I) clusters are confirmed to be icosahedral. On the other hand, the bare B12 cluster is shown to have a planar structure. A previous study showed that a transformation from an icosahedron to a plane happens when 5 to 7 iodine atoms are substituted. Later, the transition was confirmed to be seven iodine substitutions based on an infrared spectroscopy study. In this study, we investigated the effects of different halogen atoms on the opening of the B12 icosahedral cage by means of density functional theory calculations. We found that the halogen elements do not have significant effects on the geometries of the clusters. The computed IR spectra show similar representative peaks for all halogen substituted clusters. Interestingly, we found a blue-shift in the IR spectra with the increase in the mass of the halogen atoms. Further, we compared the Gibbs free energies at different temperatures for different halogen atoms. The results show that the Gibbs free energy differences between open and close structures of B12X7 become larger when heavier halogen atoms are present. This interesting finding was subsequently investigated by energy decomposition analysis.