Planar hexacoordinate gallium

Abstract

We report the first planar hexacoordinate gallium (phGa) center in the global minimum of the GaBe₆Au₆ ⁺ cluster which has a star-like D _6h geometry with ¹A_1g electronic state, possessing a central gallium atom encompassed by a Be₆ hexagon and each Be-Be edge is further capped by an Au atom. The electronic delocalization resulting in double aromaticity (both σ and π) provides electronic stability in the planar form of the GaBe₆Au₆ ⁺ cluster. The high kinetic stability of the title cluster is also understood by Born-Oppenheimer molecular dynamics simulations. The energy decomposition analysis in combination with the 'natural orbitals for chemical valence' theory reveals that the bonding in the GaBe₆Au₆ ⁺ cluster is best expressed as the doublet Ga atom with 4s²4p_⊥ ¹ electronic configuration forming an electron-sharing π bond with the doublet Be₆Au₆ ⁺ moiety followed by Ga(s)→[Be₆Au₆ ⁺] σ-backdonation and two sets of Ga(p_‖)←[Be₆Au₆ ⁺] σ-donations.