S-Bridged Polynuclear Complexes. I. Selective Formation and Crystal Structure of (+)600CD-Bis[tris( l -cysteinato-N,S)cobaltate(III)-μ-S,μ-S′,μ-S″]cobalt(III) Nitrate Pentahydrate

The crystal structure and the absolute configuration of the selectively formed title isomer, (+)600CD-[Co{Co(l-cys-N,S)3}2](NO3)2·5H2O, have been determined by X-ray diffraction. In the (+)600CD isomer, the six l-cysteinates coordinate through the nitrogen and sulfur atoms to give two terminal [Co(l-cys-N,S)3] moieties. The central cobalt atom spans the six sulfur atoms in these terminals to form a trinuclear structure. The (+)600CD isomer takes selectively a ΛLLLΛLLL configuration, in which both of the two terminals have a ΛLLL-fac(S) configuration, and the six sulfur donor atoms take an R one. The l-cysteinate chelate rings take a lel conformation along the C3 axis and the carboxyl or carboxylato groups take the axial orientations forming the intramolecular hydrogen bonds. The (−)600CD isomer is assigned to the ΔLLLΔLLL configuration on the basis of the electronic absorption, CD, and 13C NMR spectral behaviors. The selective formation for each of the (+)600CD and (−)600CD isomers is discussed in relation to their reaction conditions.