A Square As 4 and a Prismatic As 6 Structure as Complex Ligands

[As 7 (SiMe 3 ) 3 ] reacts with [(Cp * CoCl) 2 ] to give black crystals of the ionic compound [(Cp * Co) 3 As 6 ][CoCl 4 ] ( 1 ). The cation [(Cp * Co) 3 As 6 ] 2+ consists of an As 6 prism, with squares capped by [Cp * Co] fragments. When [(Cp t Bu CoCl) 2 ] is used instead of [(Cp * CoCl) 2 ] in the reaction, dark red crystals of [(Cp t Bu Co) 3 As 6 ][CoCl 3 (thf)] 2 ( 2 ) and green–black crystals of [(Cp t Bu Co) 2 As 4 ][Co 3 Cl 8 (thf) 2 ] ( 3 ) can be obtained. The cation in 2 shows a structure very similar to that of 1 . The [(Cp t Bu Co) 2 As 4 ] 2+ cations in 3 can be described as a triple‐decker sandwich complex with two [Cp t Bu Co] + fragments bridged by an As 4 ligand. Density functional calculations reproduce the experimental data of 1 and 3 and allow an interpretation of molecular electronic structure and bonding in these and related compounds with As replaced by P and Co by Fe.