Cl©K ₄ I ₄ – : A Star-Like Planar Tetracoordinate Chlorine Superhalogen Anion

A planar tetracoordinate chlorine anion, Cl©K₄I₄⁻, is identified as a global minimum, in which a central chlorine atom is embedded within a square K₄ framework bridged by four peripheral iodine atoms. This assignment is supported by unbiased isomer searches at the density functional theory level combined with high-level single-point CCSD(T) calculations. Born-Oppenheimer molecular dynamics simulations confirm its dynamical stability. Bonding analyses indicate that stabilization of the planar tetracoordinate chlorine center is dominated by electrostatic interactions. The anion exhibited a large first vertical detachment energy of 6.09 eV at the single-point CCSD(T)/def2-TZVPPD level, describing it as a superhalogen anion. The coexistence of planar tetracoordinate chlorine coordination and superhalogen character identifies Cl©K₄I₄⁻ as a viable target for future gas-phase experimental characterization.