Bi-Zn bond formation in liquid ammonia solution: [Bi-Zn-Bi]^4-, a linear polyanion that is Iso(valence)-electronic to CO₂

Reactions of the zinc(I) complex [Zn₂(Mesnacnac)₂] (Mesnacnac=[(2,4,6-Me₃C₆H₂)NC(Me)] ₂CH) with solid K₃Bi₂ dissolved in liquid ammonia yield crystals of the compound K₄[ZnBi₂] ·(NH₃)₁₂ (1), which contains the molecular, linear heteroatomic [Bi-Zn-Bi]^4- polyanion (1a). This anion represents the first example of a three-atomic molecular ion of metal atoms being iso(valence)-electronic to CO₂ and being synthesized in solution. The analogy of the discrete [Bi-Zn-Bi]^4- anion and the polymeric ¹_∞ [(ZnBi_4/2)^4-] unit to monomeric CO₂ and polymeric SiS₂ is rationalized.