Tetrahedral [Sb(AuMe)4]3− Occurring in Multimetallic Cluster Syntheses: About the Structure-Directing Role of Methyl Groups

The anion of [K(crypt-222)]3[Sb(AuMe)4]·py (1; crypt-222 = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane; py = pyridine) represents a rare example of a homoleptic heavy p-block metal atom being surrounded by four free-standing transition metal complex fragments, and the third example for a corresponding Sb compound. In contrast to all reported complexes of this type, the transition metal atoms possess twofold coordination only, hence the complex as a whole does not exhibit significant steric shielding or further linkage of the metal atoms. This is reflected in a high flexibility, as confirmed by slight deviations from a tetrahedral coordination of the Sb atom in the crystal and soft vibrational modes. An alternative pyramidal conformer, observed for a related arsenic compound with terminal phosphine ligands, is apparently disfavored owing to electron correlation effects. The compound is formed in a reaction that in another solvent or at other reactant concentrations yields salts of ternary cluster anions. By a combined experimental and theoretical study of different reaction conditions and previously unidentified side-products, we provide insight into multimetallic cluster synthesis reactions.