Alkali-Noble Metal Synergy in F©Li₄M₄^– (M = Ag, Au): A Novel Ionic Framework for Stabilizing Planar Tetracoordinate Fluorine

Planar tetracoordinate fluorine (ptF) has long been considered elusive due to the high electronegativity and lone-pair rigidity of fluorine. Herein, we report the star-like ptF clusters in noble metal-bridged clusters F©Li₄M₄^- (M = Ag, Au) via a purely ionic mechanism. Combining density functional theory (DFT) and coupled-cluster calculations, these <i>D</i>_4<i>h</i>-symmetric global minima feature a central F^- electrostatically confined by a Li₄ square with Ag/Au bridges optimizing the cavity size. Natural bond orbital analysis shows that there is a substantial charge transfer between F and Li, while covalency is almost negligible. Born-Oppenheimer molecular dynamics simulations reveal their excellent dynamic stability at room temperature. The high vertical detachment energies (3.62 and 5.07 eV) classify them as superhalogen anions. Notably, the stability of these clusters is not reliant on aromaticity; rather, it is primarily governed by electrostatic interactions. This work expands the field of ptF chemistry and highlights the role of noble metals as geometric enablers for ionic hypercoordination.