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.