Flexible Cu^I-thiolate clusters with relevance to metallothioneins

Abstract

Simple Cu-thiolate chemistry was developed to demonstrate the presence of copper clusters with {Cu₄S₆}, {Cu₅S₇} and {Cu₆S₄} cores in relevance to copper-containing metallothioneins. The new hexanuclear tricoordinate triply bridging thiolatocopper(I) clusters [NEt₄]₄[Cu₆(SPh)₄Cl₆] (1) and[NEt4]4[Cu6(SPh)4Br6] (2) were synthesized from the soup of polymeric [CuISPh]n and quaternary ammonium halide. These complexes readily converted into [Et₄N]₂[Cu₅(SPh)₇] (3) and [Et₄N]₂[Cu₄(SPh)₆] (4) in the presence of excess amounts of thiol. All are structurally characterized by single-crystal X-ray crystallography and these smaller clusters may be inscribed into the structurally characterized larger cluster {Cu₈S10} obtained from synthetic copper yeast metallothioneins. Like Cu-MT proteins, all these clusters show photoluminescence around 560 nm on excitation at 350 nm, and these emission spectra are completely quenched by molecular oxygen. Variable copper stoichiometry and the interconversion of only monodentate thiolate ligands in these clusters convey the importance of flexibility, which is relevant to metallothioneins.