Planar Pentacoordinate Halogens

Planar hypercoordinate motifs represent an intriguing frontier in chemistry, challenging traditional bonding norms. As electronegativity of the central atom increases, achieving planar hypercoordination becomes more difficult due to restricted delocalization, making the design of planar hypercoordinate halogens particularly puzzling. Here, we conduct an extensive computational survey of LinXn+1- (n = 4, 5, 6; X = F, Cl, Br, I) clusters, revealing a starlike D5h-symmetry global minimum in Li5X6- (X = F, Cl, Br) with a planar pentacoordinate halogen (ppX), where X- is located at the center of Li5X5 crown. The clusters are stabilized predominantly through electrostatic interactions between X- and Li5X5, complemented by weak covalent bonding from dative interaction. Due to the weak orbital overlap, ppX clusters exhibit localized diatropic ring currents around X and Li.