The Identity of "Ternary" A/Tl/Pb or K/Tl/Bi Solid Mixtures and Binary Zintl Anions Isolated From Their Solutions

Investigations of solid mixtures of the elemental combinations A/Tl/Pb (A=Na, K) and K/Tl/Bi indicate the presence of multiple binary and ternary Zintl phases, among them new ones containing Tl and Pb or Bi, respectively. Extractions with en/crypt-222 afford single crystals of several novel binary anions, including [Tl@Tl₄ Pb₈ ]^4- and (Tl₄ Bi₃ )^3- . [Tl@Tl₄ Pb₈ ]^4- adopts a closo-type cage structure despite possessing one additional electron; it is therefore isostructural, yet not isoelectronic, with homoatomic [Tl@Tl₁₂ ]^11- obtained by solid state reactions. (Tl₄ Bi₃ )^3- is a rare case of a pentagonal bipyramidal Zintl anion, yet the first binary one, and (unlike Tl₇^7- ) the first one with a proper closo-type electron count. Assignment of the numbers and positions of the Tl/Pb or Tl/Bi atoms within the anionic clusters, indistinguishable in classical X-ray diffraction experiments, was achieved by means of quantum chemistry. The studies shed light on the complex situation in solid heavy element mixtures and their substantial differences from the composition of the Zintl anions obtained from them by extraction.