HLi₄Cl₄^-: a planar tetracoordinate hydrogen superhalogen anion

Area of Science:

• Computational Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Planar tetracoordinate hydrogen (ptH) species and superhalogen anions are rare chemical entities.
• Previous designs of ptH species often relied on specific auxiliary atoms for stabilization.

Purpose of the Study:

• To design and characterize a novel ternary ptH cluster with enhanced stability.
• To explore a new strategy for designing ptH species by modifying auxiliary atoms.
• To investigate the bonding nature and superhalogen characteristics of the designed cluster.

Main Methods:

• Unbiased isomeric searches to identify the global minimum structure.
• Born-Oppenheimer molecular dynamics simulations at 300 K and 600 K.
• Quantum chemical calculations, including bonding analysis and vertical detachment energy calculations at the CCSD(T) level.

Main Results:

• A stable ternary ptH cluster, D4h HLi4Cl4-, was successfully designed, featuring a central hydrogen atom, a Li4 square, and four chlorine bridges.
• The cluster was confirmed as a true global minimum and demonstrated robustness against isomerization and dissociation at elevated temperatures.
• Multicenter ionic bonding, including 3c-2e Li-Cl-Li and a central 5c-2e sigma bond, was identified as the primary stabilizing factor.
• The HLi4Cl4- cluster exhibits a high vertical detachment energy (7.33 eV), classifying it as a superhalogen anion.

Conclusions:

• The 'altering the auxiliary atoms' strategy is effective for designing new ptH species.
• The HLi4Cl4- cluster represents a significant advancement in ptH chemistry and superhalogen research.
• This work provides a crucial link between the fields of ptH chemistry and superhalogens.