Aggregation of fac-[Ir(aet)3](aet = 2-aminoethanethiolate) around the [Co II 4O]6+ core. Structures and some properties of spontaneously resolved S-bridged octanuclear complexes [{Ir(aet)3}4M4O]Br6(M4= Co II 4, Zn II 4 or Zn II 2.8Co II 1.2)

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Abstract
Novel S-bridged octanuclear complexes, [{Ir(aet)3}4M4O]Br6[aet = 2-aminoethanethiolate; M = CoII1, ZnII2 or M4= ZnII 2.8CoII 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 CoIII 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 CoII.

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