| Abstract
| - Two pairs of racemic isomers of[{Co2(aet)2}{Co(aet)3}2]4+(1a and 1b) were produced by the ligand transferreactions of [Ni(aet)2] (aet =2-aminoethanethiolate) with[CoCl(NH3)5]2+ or[CoCl2(en)2]+. Thecrystal structures of 1a and 1b were determinedby X-ray crystallography, which demonstrated the novel S-bridgedtetracobalt(III) structure with a boat-type metal array.1a and 1b were optically resolved, and theconfigurational assignment of their optically active isomers was madeby the CD curve analysis, considering that the CD contributions fromthe inner and the outer cobalt chiral centers areadditive.
- A novel S-bridged tetracobalt(III) complex,[{Co2(aet)2}{Co(aet)3}2]4+(1), was prepared by reacting[Ni(aet)2](aet = 2-aminoethanethiolate) with[CoCl(NH3)5]2+ or[CoCl2(en)2]+ (en =ethylenediamine) in water. 1 formedtwo pairs of racemic isomers, 1a and 1b, whichwere separated by fractional crystallization and/orcation-exchangecolumn chromatography. The crystal structures of 1a and1b were determined by X-ray crystallography.1a(NO3)4·2H2O,empirical formulaC16H52N12O14S8Co4,crystallizes in the triclinic space group P1̄ witha =13.585(3) Å, b = 15.132(3) Å, c =10.699(2) Å, α = 101.46(1)°, β =104.78(1)°, γ = 95.89(1)°, and Z =2.1b(NO3)4·2H2Ocrystallizes in the monoclinic space group Cc witha = 26.633(6) Å, b = 10.204(1) Å,c =15.907(4) Å, β = 110.33(1)°, and Z = 4.Each of 1a and 1b contains four cobalt atomswhich are linked by onedouble and two triple sulfur bridges in a boat-type metal array.The two outer cobalt atoms have afac-Co(N)3(S)3 chromophore, while the two inner cobalt atoms have aCo(N)(S)5 chromophore. The isomers possiblefor 1are discriminated by a combination of the Δ or Λ configuration forthe outer cobalt centers and the C orAconfiguration for the inner cobalt centers, and X-ray analysesindicated that 1a and 1b have theΔAAΔ/ΛCCΛand ΔCCΔ/ΛAAΛ configurations,respectively. Each of 1a and 1b wasoptically resolved, and their electronicabsorption, circular dichroism (CD), and NMR spectral properties arealso reported. The additivity on CD wasconsidered to assign the absolute configuration for the opticallyresolved isomers of 1a and 1b.
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