A multicentre-bonded [ZnI]8 cluster with cubic aromaticity

Polynuclear zinc clusters [Znx] (x>2) with multicentred Zn-Zn bonds and +1 oxidation state zinc (that is, zinc(I) or Zn-I) are to our knowledge unknown in chemistry. Here we report the polyzinc compounds with an unusual cubic [Zn-8(I)(HL)(4)(L)(8)](12) (-) (L = tetrazole dianion) cluster core, composed of zinc(I) ions and short Zn-Zn bonds (2.2713(19) angstrom). The [Zn-8(I)]bearing compounds possess surprisingly high stability in air and solution. Quantum chemical studies reveal that the eight Zn 4s(1) electrons in the [Zn-8(I)] cluster fully occupy four bonding molecular orbitals and leave four antibonding ones entirely empty, leading to an extensive electron delocalization over the cube and significant stabilization. The bonding pattern of the cube represents a class of aromatic system that we refer to as cubic aromaticity, which follows a 6n + 2 electron counting rule. Our finding extends the aromaticity concept to cubic metallic systems, and enriches Zn-Zn bonding chemistry.