Syntheses of linear-type S-bridged trinuclear complexes composed of heavy d6 metal ions and 2-aminoethanethiolate: comparative characterization by X-ray diffraction, spectroscopy and electrochemistry

The S-bridged trinuclear complexes composed of heavy d6 metal ions, [RhIII{M(aet)3}2]3+ (M=IrIII(1), RhIII(2); aet = 2-aminoethanethiolate), have been prepared by the reactions of fac(S)-[M(aet)3] with RhCl3 · 3H2O. The complexes were separated into meso (1a, 2a) and rac (1b, 2b) isomers by SP-Sephadex C-25 column chromatography. 1b and 2b were optically resolved by the column chromatographic method and characterized by CD spectroscopy. Crystal structures of 1a, 1b and 2a were determined by X-ray diffraction, and it was found that they consist of linear-type trinuclear structures. The central Rh(III) ion in the present complexes has d6 electronic configuration with the non-degenerated A-type cubic field term, and showed long Rh⋯M distances, acute S–M–S angles and obtuse Rh–S–M angles. These are in contrast with the complexes having the degenerated T-type cubic field term such as [M′{M(aet)3}2]n+ (M′=VIII, MoIV and ReIII, M=IrIII, RhIII, n=3 or 4). All the isomers have been comparatively characterized and discussed in solid state and the solution for spectrochemical and electrochemical properties.