H©Cu₄I₄^–: A Planar Tetracoordinate Hydrogen Superhalogen Anion Stabilized by Covalent Multicenter Bonding

Planar tetracoordinate hydrogen (ptH) superhalogen anions are very rare. To date, only a few examples dominated by electrostatic interactions have been reported. Herein, using Cu as the ligands and I as the auxiliary bridges, we computationally design a star-like ptH H©Cu₄I₄^- cluster, which is a global minimum (GM) based on unbiased structural searches, followed by high-level quantum chemical calculations. Born-Oppenheimer molecular dynamics simulations show the resistance of the ptH H©Cu₄I₄^- GM to deformation and isomerization. Chemical bonding analyses reveal that there is one delocalized 5c-2e σ bond over the HCu₄ core and four Cu-I-Cu 3c-2e σ bonds along the periphery, except for the lone pairs (LPs). These covalent multicenter bonds dominate the stability of the system rather than aromaticity. Encouragingly, H©Cu₄I₄^- has a high vertical detachment energy (4.74 eV) at the single-point CCSD(T)/def2-TZVPP level and can be viewed as a superhalogen anion. It represents the first covalent bonding dominated ptH superhalogen anion, enriching the ptH chemistry as well as superhalogens.