Planar hexacoordinate chlorine

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.