Versatile Coordination of Ag and Cu Ions towards cyclo-As Ligands.

The reactions of the cyclo-As complex [Cp*Fe(η -As )] (B) with the Ag and Cu salts of the weakly coordinating anion (WCA) [FAl{OC F (C F )} ] ([FAl] ) are studied. These reactions allow the synthesis of the mononuclear complexes [M(η  : η -B) ][FAl] (M=Ag (1), Cu (2)) when a ratio of B/M(FAl) 2 : 1 is used. Compound 1 shows an unusual disorder of the central Ag cation between two π-coordinating cyclo-As ligands, which is absent in 2 pointing to a weak interaction of the Ag center towards the cyclo-As ligands in B. When the ratio of B/Ag(FAl) is changed to 3 : 1 or 1 : 1, the respective coordination compounds [Ag(η -B) ][FAl] (3) and [Ag (η  : η -B) ][FAl] (4) are accessible. The coordination modes of the cyclo-As units in 1, 3 and 4 are all different, reflecting the adaptive coordination behavior of B towards Ag ions. The optimized geometries in the gas phase of 1-4 are determined by DFT calculations to support the bonding situation observed in their solid-state structures.