Synthesis and crystal structure of [Li(NH3)4]4[Sn9]·NH3 and [Li(NH3)4]4[Pb9]·NH3

Abstract

The reduction of an excess of Sn or Pb with a concentrated solution of Li in liquid ammonia yielded black crystals of [Li(NH₃)₄]₄[Sn₉]·NH₃ or [Li(NH₃)₄]₄[Pb₉]·NH₃ as main product, respectively. The compounds are isotypic and crystallise in space group P2₁/c. They contain the isolated Zintl anions Sn₉⁴⁻ and Pb₉⁴⁻, which form slightly distorted monocapped square antiprisms. The lead compound is the first example of a “naked” Pb₉⁴⁻ cage without contacts to metal atoms.