Synthesis, characterisation and polynuclearisation reaction of trans(S)-[Co(aminothiolate-N,S)(2)(en)]-type cobalt(III) complexes with 2-aminoethanethiolate, L-cysteinate and D-penicillaminate

The trans(S)-[Co(N)(4)(S)(2)]-type mononuclear complexes [Co(L)(2)(en)](+or -) (L=2- aminoethanethiolate (aet) 1, L-cysteinate (L-cys) 3 or D-penicilla minate (3-sulfanyl-D-valinate) (D-pen) 5) were newly prepared by the reacti on of trans-[CoCl2(en)(2)](+) with L at pH 8.5 and 25 degrees C. The crysta l structure of 1 was determined by X-ray diffraction analysis. The geometry around the cobalt atom is approximately octahedral and two thiolate donor atoms in the aet ligands occupy trans positions to each other. Two Co-S bon ds are lengthened by the double sulfur trans influence across the cobalt ce ntre attributable to two thiolato sulfur donor atoms. The diastereomers of 3 and 5 were separated by the column chromatographic technique and characte rised on the basis of their UV/Vis, CD and C-13 NMR spectra. The Lambda(DD) isomer of 5 (5 Lambda(DD)) is preferably formed by attractive (COO ... H-N -H) interactions. Though cis(S)-[Co(L)(2)(en)](+or-) (L=aet 2, L-cys 4 or D -pen 6) were also produced by the same preparative reaction, they could not be separated into the geometrical isomers because of very rapid isomerisat ion and/or polynuclearisation reaction during elution from the column. It i s clear that all trans(S) complexes also show drastic and characteristic UV /Vis spectral changes with time in aqueous solutions and tend to isomerise to the cis(S) isomer, followed by the formation of S-bridged polynuclear co mplexes owing to both the double sulfur trans influence and high nucleophil icity of the thiolate donor atoms. The polynuclearisation reactions of the three trans(S) isomers proceed according to different processes depending o n their ligands. In the polynuclearisation reaction of 3, especially, the n ovel dinuclear complex Lambda(LLL)-[Co{Co(L-cys-N,S)(3)}(L-cys- >$($) over bar N,O,S)](2-) 7, which has not so far been identified in usual dinucleari sation reactions, was newly obtained.