Why Do Five Ga+ Cations Form a Ligand-Stabilized [Ga5]5+ Pentagon and How Does a 5:1 Salt Pack in the Solid State?

Abstract

The reaction of the Ga+ source [Ga(PhF)2]+[Al(ORF)4]− with the neutral σ-donor ligand dmap (4-Me2N-C6H4N) produces the unexpectedly large and fivefold positively charged cluster cation salt [Ga5(dmap)10]5+([Al(ORF)4]−)5. It includes a regular and planar Ga5 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 4s2 lone-pair orbitals into fully Ga-Ga-bonding orbitals and the solid-state arrangement of the ions constituting the lattice as an almost orthohexagonal AX5 lattice, possibly the aristotype of any 5:1 salt.