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 dimethylform amide 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.