Aggregation of fac-[Ir(aet)3](aet = 2-aminoethanethiolate) around the [CoII4O]6+ core. Structures and some properties of spontaneously resolved S-bridged octanuclear complexes [{Ir(aet)3}4M4O]Br6(M4= CoII4, ZnII4 or ZnII2.8CoII1.2)

Abstract

Novel S-bridged octanuclear complexes, [{Ir(aet)₃}₄M₄O]Br₆[aet = 2-aminoethanethiolate; M = Co^II1, Zn^II2 or M₄= Zn^II_2.8Co^II_1.23], containing a tetrahedral M₄O core, have been prepared. In the octanuclear complexes, the cobalt(II) oxidation state is stabilized and the species are not oxidized to Co^III either in the crystalline state or in aqueous solution. The crystal structure and absolute configuration of the spontaneously resolved (–)₃₀₀^CD, isomer for each of 1 and 3 were determined by single-crystal X-ray diffraction. The four octahedral fac-[Ir(aet)₃] sub-units aggregate around the tetrahedral [M₄O]⁶⁺ core in a tetrahedral arrangement. The chiral configurations of the (–)₃₀₀^CD isomer for each of 1 and 3 is Δ for all four fac-[Ir(aet)₃] sub-units and S for all 12 bridging sulfur atoms. Cyclic voltammetric measurements for 1 in water exhibited a reversible redox couple at –0.97 V (vs. Ag–AgCl), which corresponds to the [Co₄O]⁶⁺–[Co₄O]⁵⁺ redox reaction. The electronic absorption, circular dichroism (CD), ¹H and ¹³C NMR spectral behaviour of these complexes are discussed in relation to the geometry of the tetrahedral Co^II.