Sulfur-bridged Co(III)Pt(II)Co(III) trinuclear complexes with mixed aliphatic and aromatic thiolate ligands: effect of nonbridging ligands on the homochiral linkage of cobalt(III) octahedrons by platinum(II).

The reaction of NiCo(aet)(2)(pyt) (aet = 2-aminoethanethiolate, pyt = 2-pyridinethiolate) with PtCl(4)(-) gave an S-bridged Co(III)Pt(II)Co(III) trinuclear complex composed of two [Co(aet)(2)(pyt)] units, PtCo(aet)(2)(pyt) (1). When a 1:1 mixture of NiCo(aet)(2)(pyt) and NiCo(aet)(2)(en) was reacted with PtCl(4)(-), a mixed-type S-bridged Co(III)Pt(II)Co(III) complex composed of one [Co(aet)(2)(pyt)] and one Co(aet)(2)(en) units, Pt[Co(aet)(2)(en)][Co(aet)(2)(pyt)] (2), was produced, together with 1 and PtCo(aet)(2)(en). The corresponding Co(III)Pt(II)Co(III) trinuclear complexes containing pymt (2-pyrimidinethiolate), PtCo(aet)(2)(pymt) (3) and Pt[Co(aet)(2)(en)][Co(aet)(2)(pymt)] (4), were also obtained by similar reactions, using NiCo(aet)(2)(pymt) instead of NiCo(aet)(2)(pyt). While PtCo(aet)(2)(en) formed both the deltalambda (meso) and deltadelta/lambdalambda (racemic) forms in a ratio of ca. 1:1, the preferential formation of the deltadelta/lambdalambda form was observed for 1 (ca. deltalambda:deltadelta/lambdalambda = 1:3) and 2 (ca. delta(en)lambda(pyt)/lambda(en)delta(pyt):deltadelta/lambdalambda = 1:2). Furthermore, 3 and 4 predominantly formed the deltadelta/lambdalambda form. These results indicate that the homochiral selectivity for the S-bridged Co(III)Pt(II)Co(III) trinuclear complexes composed of two octahedral [Co(aet)(2)(L)](0 or +) units is enhanced in the order L = en < pyt < pymt. The isomers produced were separated and optically resolved, and the crystal structures of the meso-type deltalambda-[1]Cl(2).4H(2)O and the spontaneously resolved deltadelta-4(3).H(2)O were determined by X-ray analyses. In deltalambda-1, the delta and Lambda configurational mer(S).trans(N(aet))-[Co(aet)(2)(pyt)] units are linked by a square-planar Pt(II) ion through four aet S atoms to form a linear-type S-bridged trinuclear structure. In deltadelta-4, a similar linear-type trinuclear structure is constructed from the delta-mer(S).trans(N(aet))-[Co(aet)(2)(pymt)] and delta-C(2)-cis(S)-Co(aet)(2)(en) units that are bound by a Pt(II) ion with a slightly distorted square-planar geometry through four aet S atoms.