[Bi4]6– – The Zintl Anion with the Highest Charge per Atom Obtained from Solution


  • Dedicated to Professor Bernt Krebs on the Occasion of His 75th Birthday

  • Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/zaac.201300464 or from the author.


From the dark-purple solution of the Zintl phase KBi in liquid ammonia dark-blue crystals of the ammonia solvate K6[Bi4](NH3)8 were obtained. In contrast to known Bin polyanions the chemical bond in the anion [Bi4]6– is in accordance with the (8-N) rule featuring solely Bi–Bi single bonds. [Bi4]6– is a butane-analog valence compound, and with 6 negative charges per 4 atoms it is the anion with the highest known charge per atom obtained from solution. The planarity of the trans-[Bi4]6– unit hints at π orbital contributions of the bismuth atoms. The corresponding reactions of the phases K5Bi4 and K3Bi2 in liquid ammonia in the presence of [2.2.2]crypt(4, 7, 13, 16, 21, 24-hexaoxa-1, 10-diazabicyclo-[8.8.8]hexacosane) lead to the salt [K([2.2.2]crypt)]2[Bi2](NH3)4 with the known electron-deficient [Bi2]2– polyanion and a Bi=Bi double bond.