Planar hexacoordinate sulfur and selenium

Abstract

Planar hexacoordinate atoms are challenging to achieve. The first planar hexacoordinate sulfur and selenium (phS/Se) X©Li6H62− (X = S, Se) clusters were predicted. High-level quantitative calculations reveal that the global minima of X©Li6H62− (X = S, Se) adopt singlet D6h-symmetric structures, each consisting of a central S/Se atom coordinated by a Li6 hexagon, with every Li–Li edge further capped by an H atom. Born–Oppenheimer molecular dynamics simulations confirm that the phX structures of X©Li6H62− (X = S, Se) are robust. Furthermore, bonding analyses reveal that there is one lone pair for the central S2−/Se2−, three delocalized σ bonds within the S©Li6/Se©Li6 core, and six delocalized 3c–2e σ bonds along the periphery. Energy decomposition analysis—natural orbitals for chemical valence analysis—indicates that electrostatic interactions dominate between phS/Se and the Li6H6 ring, with a contribution rate of 75.8% and 75.6%. The stability of the phS/Se center is dominated by multicenter ionic bonds. The current results not only break the conventional coordination limit for chalcogen elements but also motivate further theoretical and experimental studies on novel phS/phSe complexes.