Planar Hexacoordinate Chlorine

Abstract

Cl©Zn6O6– is identified as a genuine global minimum, which contains a planar hexacoordinate chlorine atom, extending the coordination limit of halogens from five to six. An exhaustive potential energy surface exploration, combined with high-level CCSD(T)/aug-cc-pVTZ calculations, confirms its thermodynamic stability, while Born–Oppenheimer molecular dynamics shows that the planar framework retains its structural integrity up to 900 K. Bonding analyses indicate that Cl©Zn6O6– is stabilized predominantly by multicenter ionic interactions between Cl– and the Zn6O6 ring. The electronic structure features four Cl lone pairs, Zn–O σ bonds, Zn–O–Zn π bonds, and electrostatic Cl–Zn interactions. With a HOMO–LUMO gap of 5.31 eV and a vertical detachment energy of 7.40 eV, Cl©Zn6O6– qualifies as a superhalogen anion. These results show the coexistence of planar hypercoordination and superhalogen character, establishing structural and electronic principles for designing planar hypercoordinate superhalogens.