Bismuth polyanions in solution: Synthesis and structural characterization of (2,2,2-crypt-A)₂Bi₄ (A = K, Rb) and the formation of the laves phases ABi₂ (A = K, Rb, Cs) from solution

The possibility to synthesize and isolate different types of bismuth polyanions by dissolving various intermetallic precursors (binary samples from A-Bi or ternary samples from A-A'-Bi systems, A and A' = K, Rb, Cs) in ethylenediamine or dimethylformamide in the presence of sequestering agents (2,2,2-crypt or 18-crown-6) was investigated. The crystals of (2,2,2-crypt-K)₂Bi₄ (1) and (2,2,2-crypt-Rb)₂Bi₄ (2) compound were obtained from such solutions, the latter for the first time, and their structures were determined. The two compounds are isostructural (P1, Z = 1, a = 11.052(2) Å, b = 11.370(2) Å, c = 11.698(2) Å, α = 61.85(3)°, β = 82.58(3)°, γ = 81.87(3)°, R₁ = 0.058, wR² = 0.149 for 1 and a = 11.181(2) Å, b = 11.603(2) Å, c = 11.740(2) Å, α = 61.96(3)°, β = 81.45(3)°, γ = 82.26(3)°, R₁ = 0.041, wR² = 0.109) and contain Bi₄^2- square planar cluster anions and cryptated alkali metal cations. In the case of the presence of 18-crown-6 the Laves phases ABi₂ (A = K, Rb, Cs) could be isolated from the solutions. A mechanism for the formation of ABi₂ is proposed.