Cyanido Antimonate(III) and Bismuthate(III) Anions

The reaction of in situ generated E(CN)₃ (E = Sb, Bi) with different amounts of [Ph₄P]CN and [PPN]CN ([PPN]⁺ = [Ph₃P-N-PPh₃]⁺) was studied, affording salts bearing the novel ions [E(CN)₅]^2-, [Bi₂(CN)₁₁]^5-, and [Bi(CN)₆]^3-. The valence lone pair of electrons on the central atom of antimony and bismuth(III) compounds can be either sterically active in an unsymmetric fashion (three shorter bonds + x longer bonds) or symmetric (with rather long averaged bonds). In the presence of weakly coordinating cations (e.g., [Ph₄P]⁺ and [PPN]⁺), the solid-state structures of salts with [E(CN)₅]^2- anions contain well-separated cations and monomeric anions, which display a sterically active lone pair and a monomeric square-based pyramidal (pseudo-octahedral) structure. The [Bi(CN)₅·MeCN]^2- acetonitrile adduct ion exhibits a strongly distorted octahedral structure, which is better understood as a [5 + 1] coordination. The intriguing [Ph₄P]₆[Bi₂(CN)₁₁]CN salt consists of separated cations and anions as well as well-separated [Bi₂(CN)₁₁]^5- and CN^- ions. The structure of the molecular [Bi₂(CN)₁₁]^5- ion can be described as two square-based-pyramidal [Bi(CN)₅]^2- fragments connected by a disordered bridging CN^- ion, thereby leading to a distorted-octahedral environment around the two Bi centers. Here the steric effect of the lone pair is much less pronounced but still present.