Crystal structures and spectroscopic characterization of linear-type S-bridged trinuclear complexes Delta Lambda- and Delta Delta/Lambda Lambda-[Re-III{Rh-III(aet)(3)}(2)](3+) (aet=2-aminoethanethiolate)

The reduction of an acidic mixture of fac(S)-[Rh-III(aet)(3)] (aet = 2-amin oethanethiolate) and (NH4ReO4)-O-VII gave the first linear-type S-bridged t rinuclear complexes containing a d(4) metal ion, [Re-III{Rh-III(aet)(3)}(2) ](3+). The meso (1a) and racemic (1b) isomers were selectively isolated by using HCl and HBr solutions, respectively, although both isomers were forme d in each case. The crystal structures of 1aCl(ReO4)(2). 4H(2)O and 1b(ClO4 )(3) were determined by X-ray crystallography. Both complex cations consist of two terminal fac(S)-[Rh-III(aet)(3)] units and a central rhenium, atom, which is situated in an octahedral environment with the (ReS6)-S-III chrom ophore. Ib was optically resolved by a column chromatographic method and ch aracterized by CD spectroscopy. la and Ib were fairly stable in water, even under aerobic conditions, unlike in the case of previously reported [Mo-II I{Rh-III(aet)(3)}(2)](3+). The Re(III) ion, which is incorporated into the S-bridged polynuclear structure, indicated a lower magnetic moment (1.32 mu (B) for 1b) at room temperature than the spin-only value for the d(4) elec tronic configuration. The H-1 and C-13 NMR spectra of la and Ib showed para magnetic shifts compared with those of the corresponding diamagnetic comple xes, [Co-III{Rh-III(aet)(3)}(2)](3+). 1a and 1b were also characterized on the basis of the IR and UV-vis absorption spectra and the molar conductivit ies.