SLi₄X₃^- (X = Cl, Br, I): fan-shaped superhalogen anions featuring planar tetracoordinate sulfur

The first planar tetracoordinate sulfur (ptS) SLi₄X₃^- (X = Cl, Br, I) mono-anionic clusters have been designed by using the "partially eliminating after isoelectonic-replacing" strategy, inspired by the previously reported ptF FLi₄X₄^- (X = Cl, Br, I) clusters. They are true ptS global minima featuring fan-shaped structures with a SLi₄ core and three peripheral X bridges. They are also dynamically stable at room temperature, according to Born-Oppenheimer molecular dynamics simulations. Chemical bonding analyses indicate that the ptS centers are mainly ionically connected to the Li ligands, due to their significant difference in electronegativity. Encouragingly, the exotic SLi₄X₃^- (X = Cl, Br, I) clusters have ground-state vertical detachment energies of 4.33, 4.60, and 4.90 eV at the OVGF/def2-TZVPP level, respectively, which are greater than the electron affinity of the chlorine atom (3.61 eV) and can be considered as the superhalogen anions. The current work not only presents a new strategy for designing ptS species but also builds an important link between ptS and superhalogens.