Sulfur-Bridged Co^IIIPt^IICo^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 [Ni{Co(aet)2(pyt)}2]2+ (aet = 2-aminoethanethiolate, pyt = 2-pyridinethiolate) with [PtCl4]2- gave an S-bridged CoIIIPtIICoIII trinuclear complex composed of two [Co(aet)2(pyt)] units, [Pt{Co(aet)2(pyt)}2]2+ ([1]2+). When a 1:1 mixture of [Ni{Co(aet)2(pyt)}2]2+ and [Ni{Co(aet)2(en)}2]4+ was reacted with [PtCl4]2-, a mixed-type S-bridged CoIIIPtIICoIII complex composed of one [Co(aet)2(pyt)] and one [Co(aet)2(en)]+ units, [Pt{Co(aet)2(en)}{Co(aet)2(pyt)}]3+ ([2]3+), was produced, together with [1]2+ and [Pt{Co(aet)2(en)}2]4+. The corresponding CoIIIPtIICoIII trinuclear complexes containing pymt (2-pyrimidinethiolate), [Pt{Co(aet)2(pymt)}2]2+ ([3]2+) and [Pt{Co(aet)2(en)}{Co(aet)2(pymt)}]3+ ([4]3+), were also obtained by similar reactions, using [Ni{Co(aet)2(pymt)}2]2+ instead of [Ni{Co(aet)2(pyt)}2]2+. While [Pt{Co(aet)2(en)}2]4+ formed both the ΔΛ (meso) and ΔΔ/ΛΛ (racemic) forms in a ratio of ca. 1:1, the preferential formation of the ΔΔ/ΛΛ form was observed for [1]2+ (ca. ΔΛ:ΔΔ/ΛΛ = 1:3) and [2]3+ (ca. ΔenΛpyt/ΛenΔpyt:ΔΔ/ΛΛ = 1:2). Furthermore, [3]2+ and [4]3+ predominantly formed the ΔΔ/ΛΛ form. These results indicate that the homochiral selectivity for the S-bridged CoIIIPtIICoIII 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 ΔΛ-[1]Cl2·4H2O and the spontaneously resolved ΔΔ-[4](ClO4)3·H2O were determined by X-ray analyses. In ΔΛ-[1]2+, the Δ and Λ configurational mer(S)·trans(Naet)-[Co(aet)2(pyt)] units are linked by a square-planar PtII ion through four aet S atoms to form a linear-type S-bridged trinuclear structure. In ΔΔ-[4]3+, a similar linear-type trinuclear structure is constructed from the Δ-mer(S)·trans(Naet)-[Co(aet)2(pymt)] and Δ-C2-cis(S)-[Co(aet)2(en)]+ units that are bound by a PtII ion with a slightly distorted square-planar geometry through four aet S atoms.