Planar tetracoordinate fluorine atoms in binary M₄F₄ ⁻ (M = Li, Na) clusters have been predicted using quantum chemical methods.

Planar tetracoordinate fluorine (ptF) species are rare and exotic due to the extreme electronegativity of fluorine. Herein, a ptF species is predicted in the binary Li₄F₄ ⁻ and Na₄F₄ ⁻ clusters. The global minimum of the clusters features C _2v geometry and are stabilized by significant electrostatic interaction. Moreover, multicenter ionic bonds also play a vital role in the stability of the planar C _2v geometry. The present study establishes the first example of ptF center in binary alkali halide cluster.