Stereosensitive formation and interconversion of sulfur-bridged cobalt(III)–mercury(II) polynuclear complexes with d- and/or l-penicillaminates

The reaction of trans(N)-[Co(d-pen)2]− (pen = penicillaminate) with HgCl2 or HgBr2 in the molar ratios of 1:1 gave the sulfur-bridged heterodinuclear complex, [HgX(OH2){Co(d-pen)2}] (X = Cl (1a) or Br (1b)). A similar reaction in the ratio of 2:1 produced the trinuclear complex, [Hg{Co(d-pen)2}2] (1c). The enantiomers of 1a and 1c, [HgCl(OH2){Co(l-pen)2}] (1a′) and [Hg{Co(l-pen)2}2] (1c′), were also obtained by using trans(N)-[Co(l-pen)2]− instead of trans(N)-[Co(d-pen)2]−. Further, the reaction of cis · cis · cis-[Co(d-pen)(l-pen)]− with HgCl2 in the molar ratio of 1:1 resulted in the formation of [HgCl(OH2){Co(d-pen)(l-pen)}] (2a). During the formations of the above six complexes, 1a, 1b, 1c, 1a′, 1c′, and 2a, the octahedral Co(III) units retain their configurations. On the other hand, the reaction of cis · cis · cis-[Co(d-pen)(l-pen)]− with HgCl2 in the molar ratio of 2:1 gave not [Hg{Co(d-pen)(l-pen}2] but [Hg{Co(d-pen)2}{Co(l-pen)2}] (2c), accompanied by the ligand-exchange on the terminal Co(III) units. The X-ray crystal structural analyses show that the central Hg(II) atom in 1c takes a considerably distorted tetrahedral geometry, whereas that in 2c is of an ideal tetrahedron. The interconversion between the complexes is also examined. The electronic absorption, CD, and NMR spectral behavior of the complexes is discussed in relation to the crystal structures of 1c and 2c.