Why Do Five Ga Cations Form a Ligand-Stabilized [Ga ] Pentagon and How Does a 5:1 Salt Pack in the Solid State?

The reaction of the Ga source [Ga(PhF) ] [Al(OR ) ] with the neutral σ-donor ligand dmap (4-Me N-C H N) produces the unexpectedly large and fivefold positively charged cluster cation salt [Ga (dmap) ] ([Al(OR ) ] ) . It includes a regular and planar Ga pentagon with strong metal-metal bonding. Additionally, the compound represents the first salt in which an ionic 1:5 packing is realized. We discuss the nature of this structure which results from the conversion of the non-bonding 4s lone-pair orbitals into fully Ga-Ga-bonding orbitals and the solid-state arrangement of the ions constituting the lattice as an almost orthohexagonal AX lattice, possibly the aristotype of any 5:1 salt.