text: Bismuth polycations form despite the fact that they possess fewer total valence electrons than would seem necessary for the number of sigma bonds. The shapes of these clusters are generally dictated by Wade's rules, which are based on the treatment of the electronic structure as delocalized molecular orbitals. The bonding can also be described with three-center two-electron bonds in some cases, such as the  cluster.
  Bismuth clusters have been observed to act as ligands for copper and ruthenium ions. This behavior is possible due to the otherwise fairly inert lone pairs on each of the bismuth that arise primarily from the s-orbitals left out of Bi–Bi bonding.