Synthesis of novel S-bridged heterotrinuclear complexes containing six-membered chelate rings:: Structural, spectroscopic, and electrochemical properties of [Co{Rh(apt)3}2]3+ (apt=3-aminopropanethiolate)

A bidentate ligand, 3-ammopropanethiolate (apt), was synthesized and treated with RhCl3-3H(2)O in basic water to yield a novel mononuclear complex, fac(S)-[Rh(apt)(3)] (1), which was characterized by spectroscopic methods. Furthermore, the reaction of 1 with COCl2-6HO in water formed the linear-type, S-bridged trinuclear complexes Delta Lambda-{Co(Rh(apt)(3)}(2)](3+) (2a) and Delta Delta/Lambda Lambda-[Co(Rh(apt)(3))(2)](3+) (2b), which were characterized by stereochemical, spectrochemical, and electrochemical methods. 2a and 2b are stable and exhibit trivalency in water. X-ray crystallographic analysis of 2a and 2b showed that all of the bridging sulfur atoms are fixed in the R configuration for the A unit and in the S configuration for the A unit, and each complex has six six-membered chelate rings, all of which are in the chair conformation. The crystal structure of the corresponding 2-aminoethanethiolate (act) trinuclear complex Delta Lambda-[Co[Rh(aet)(3))(2)](3+), (4a) was also deter-mined. The structures of 2a and 2b have some differences from that of 4a as a result of the six-membered chelate rings. The Co center dot center dot center dot Rh distances in 2a and 2b [3.0490(4) and 3.063(1) angstrom] are significantly longer than this distance in the aet complex 4a [2.9139(2) angstrom]. The UV/Vis absorption spectra of 2a and 2b indicate a shift to higher energies as compared with 4a and AA/AA-[Co{Rh(aet)(3)}(2)](3+) (4b). The chemical shifts for the NCH2 and SCH2 carbon atoms in 2a and 2b are shifted to higher fields than those for 4a and 4b in the NMR spectra. The Co-III/II redox potential values are -0.56V (2a) and -0.57V (2b) compared with -0.35V (4a) and -0.36V (4b). This shows that the Co-III state is more stable in 2a and 2b than it is in 4a and 4b. (c) Wiley-VCH Verlag GmbH & Co.