Planar hexacoordinate gallium

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.

A star-like texture containing a planar hexacoordinate gallium center is reported in the lowest energy isomer of the GaBe6Au₆⁺ cluster. High thermodynamic and kinetic stability of the title cluster makes it suitable candidate for experimental realization.