Abstract: The present invention provides a conjugatable metal cluster complex comprising a metal cluster of type Mk and a multivalent thioether ligand comprising at least two ligand subunits and having one reactive site or one protected reactive site which can be rendered reactive for conjugation, and each of said subunits having at least three thioether moieties, the thioether ligand, its production, and the use of the complex for PCR, labeling, fluorescence quenching and identification.