“…Stibenium (R 2 Sb + ) and bismuthenium ions (R 2 Bi + ), which are six-valence-electron species such as silylenes (R 2 Si) or N-heterocyclic carbenes (NHCs), have a vacant p orbital and one electron lone pair, hence are able to react as Lewis acid and base as was initially shown in homoleptic ([Me 2 Sb(SbMe 3 )]MeSbBr 3 , [132] ) and heteroleptic 1:1 complexes of the type [Ph 2 E(PPh 3 )]PF 6 (E = As, Sb, Bi). [133,134,135,136] In addition, 1:2 complexes such as [Ph 2 E(PPh 3 ) 2 ]PF 6 (E = Sb, Bi) were synthesized for the heavier pnictogens.…”