Planar hexacoordinate gallium.

We report the first planar hexacoordinate gallium (phGa) center in the global minimum of the GaBeAu cluster which has a star-like geometry with A electronic state, possessing a central gallium atom encompassed by a Be 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 GaBeAu 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 GaBeAu cluster is best expressed as the doublet Ga atom with 4s4p electronic configuration forming an electron-sharing π bond with the doublet BeAu moiety followed by Ga(s)→[BeAu ] σ-backdonation and two sets of Ga(p)←[BeAu ] σ-donations.