Preparation, stereochemistry, and reactivity of linear-type S-bridged MCrIIIM (M=RhIII, IrIII) trinuclear complexes with 2-aminoethanethiolate (aet).: Crystal structures of ΔΛ-[Cr{M(aet)3}2]3+

S-Bridged trinuclear complexes. [C-III(M(aet)(3)}(2))(3+), (M = Rh-III (1), Ir-III (2); aet = NH2CH2CH2S-) were newly prepared by the reaction of fac(S)-[M(aet)(3)] with chromium(III) nitrate. They were separated and optically resolved into the Delta Delta, Lambda Delta, and Delta Lambda isomers. Of these isomers for 1 and 2, the crystal structures of the Delta Lambda isomers (1a and 2a) were determined by an X-ray diffraction method. Each of la and 2a consists of two Sac(S)-[M(aet)(3)] subunits, a central Cr atom, three nitrates, and three water molecules, [Cr(M(aet)(3)}(2)](NO3)(3) . 3H(2)O, in which three metals are aligned so as to be exactly linear. The central Cr atom is situated in an octahedral environment with the (CrS6)-S-III chromophore, which is formed by the coordination of two terminal fac(S)-[M(aet)(3)] units. The other isomers for 1 and 2 were characterized by the absorption and CD spectra, the molar conductivity, and the magnetic susceptibility. Each cyclic voltammogram of Delta Lambda -[Cr{M(aet)(3)}(2)](3+) in water showed a reversible redox couple (M(IV)/M(III)) and an irreversible reduction wave (Cr(III)/Cr(II)). The stabilities of the S-bridged (MCrM)-M-III complexes are also discussed in relation to the Cr-S bond strengths.