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

Abstract

Abstract 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.