Planar hexacoordinate gallium.

We report the first planar hexacoordinate gallium (phGa) center in the global minimum of the GaBe 6 Au 6 + cluster which has a star-like D 6h geometry with 1 A 1g electronic state, possessing a central gallium atom encompassed by a Be 6 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 GaBe 6 Au 6 + 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 GaBe 6 Au 6 + cluster is best expressed as the doublet Ga atom with 4s 2 4p ⊥ 1 electronic configuration forming an electron-sharing π bond with the doublet Be 6 Au 6 + moiety followed by Ga(s)→[Be 6 Au 6 + ] σ-backdonation and two sets of Ga(p ‖ )←[Be 6 Au 6 + ] σ-donations.