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The reactions of fac-[Rh(aet)3] (aet=2-aminoethanethiolate) or ΔLLL-fac-[Rh(l-cys-N,S)3]3− (l-cys=l-cysteinate) with [CoCl(NH3)5]2+ produced [CoIII{RhIII(aet or l-cys-N,S)3}2]3+or3−, while the reactions with Co2+ formed [CoII{RhIII(aet or l-cys-N,S)3}2]2+or4− which were oxidized to give [CoIII{RhIII (aet or l-cys-N,S)3}2]3+or3−. These complexes were optically resolved or separated by fractional crystallization or column chromatography, and characterized from their absorption, CD and 13C NMR spectra. The reactions of fac-ΔLLL-[Rh(l-cys-N,S)3]3− with [CoCl(NH3)5]2+ or Co2+ at room temperature proceeded with retention of the starting ΔLLL configuration to give the ΔLLLΔLLL isomer, while the reaction with Co2+ at high temperature (ca. 95 °C) was accompanied by inversion to form the ΔLLLΛLLL, ΛLLLΛLLL, and ΔLLLΔLLL isomers. Cyclic voltammetric measurements of [CoIII {RhIII(aet or l-cys-N,S)3}2]3+or3− in water showed a quasi-reversible redox couple corresponding to the central Co(III)/(II) at ca. −0.3 V vs. Ag/AgCl. Their absorption and CD spectra and cyclic voltammograms are discussed in comparison with those of the corresponding [CoIII{CoIII (aet or l-cys-N,S)3}2]3+or3−.

The crystal structure and the absolute configuration of the selectively formed title isomer, (+)600CD-[Co{Co(l-cys-N,S)3}2](NO3)2·5H2O, have been determined by X-ray diffraction. In the (+)600CD isomer, the six l-cysteinates coordinate through the nitrogen and sulfur atoms to give two terminal [Co(l-cys-N,S)3] moieties. The central cobalt atom spans the six sulfur atoms in these terminals to form a trinuclear structure. The (+)600CD isomer takes selectively a ΛLLLΛLLL configuration, in which both of the two terminals have a ΛLLL-fac(S) configuration, and the six sulfur donor atoms take an R one. The l-cysteinate chelate rings take a lel conformation along the C3 axis and the carboxyl or carboxylato groups take the axial orientations forming the intramolecular hydrogen bonds. The (−)600CD isomer is assigned to the ΔLLLΔLLL configuration on the basis of the electronic absorption, CD, and 13C NMR spectral behaviors. The selective formation for each of the (+)600CD and (−)600CD isomers is discussed in relation to their reaction conditions.

tics of the singlet-singlet -* transition and reproduce the exciton CD pattern, for the following reasons. First, the CD behaviors are consistent with the theoretically anticipated pattern; that is, two CD bands in the charge-transfer region reproduce the exciton CD splitting in the long-axispolarized -* transition region. Second, the CD spectrum of (+)s46 [Cr(acac)(acaBr)(en)]+ is similar to those of (+)546-[Cr(acac)2(en)]+ and (+)546 [Cr(acaBr)2(en)]+ in both the charge-transfer and the -* transition regions. Third, two CD pairs of (+)s46 [Cr(acac)(acaBr)(en)]+ are found to be at the intermediate position between (+)546 [Cr(acac)2(en)]+ and (+)s46 [Cr(acaBr)2(en)]+ as may be predicted by the Contribution from the

The reactions of newly prepared fac(S)-[IrIII(aet)3] or ΔLLL-fac(S)-[IrIII(l-cys-N,S)3]3− with Co2+, followed by the air or H2O2 oxidation, gave linear-type S-bridged trinuclear complexes, [CoIII{IrIII(aet)3}2]3+ and ΔLLLΔLLL-[CoIII{IrIII(l-cys-N,S)3}2]3−. The aet trinuclear complex was separated and optically resolved into the ΔΛ, ΔΔ, and ΛΛ isomers and the crystal structure of the ΔΛ isomer was determined by X-ray diffraction. [Co{Ir(aet)3}2](NO3)3·2H2O, chemical formula C12H40N9S6O11CoIr2, crystallizes in the triclinic, space group with a = 8.945(2), b = 12.073(3), c = 8.849(3) Å, α = 110.36(2), β = 102.55(2), γ = 70.88(2)°, U = 841(2) Å3, Z = 1, and R = 0.059. The central Co(III) has a trigonally distorted octahedral geometry, coordinated by six thiolato sulfur atoms from the octahedral Δ- and Λ-fac(S)-[Ir(aet)3] terminals. The other trinuclear complexes were characterized by their absorption, CD, and 13C NMR spectra. The meso–racemic isomerization, which results from the cleavage of the Co–S bonds, was recognized for [Co{Ir(aet)3}2]3+ in D2O, methanol–H2O, and ethanol–H2O. The cyclic voltammogram of rac-[Co{Ir(aet)3}2]3+ in water showed two almost reversible redox couples at −0.23 V and +0.73 V (vs. Ag/AgCl). The chemical properties of the present IrIIICoIIIIrIII complexes are discussed in comparison with those of the corresponding RhIIICoIIIRhIII and CoIIICoIIICoIII complexes.