Stereospecific interactions between dinuclear complex cations involving square-planar [Pt(II)(μ-S)2(bpy)] (bpy = 2,2′-bipyridine) frameworks derived from optically active octahedral Co(III) units with d- or l-penicillaminates

The reaction of the octahedral mononuclear complex, trans(N)-[Co(l-pen-N,O,S)2]− (pen = penicillaminate), with [PtCl2(bpy)] (bpy = 2,2′-bipyridine) stereoselectively gave an optically active S-bridged dinuclear complex, [Pt(bpy){Co(l-pen)2}]Cl · 3H2O (2Cl · 3H2O), whose structure is enantiomeric to the previously reported [Pt(bpy){Co(d-pen)2}]Cl · 3H2O (1Cl · 3H2O). The mixture of equimolar amounts of 1Cl · 3H2O and 2Cl · 3H2O in H2O crystallizes as [Pt(bpy){Co(d-pen)2}]0.5[Pt(bpy){Co(l-pen)2}]0.5Cl · 7H2O (3Cl · 7H2O), in which the enantiomeric complex cations 1 and 2 are included in the ratio of 1:1. The crystal structures of 2Cl · 3H2O and 3Cl · 7H2O were determined by X-ray crystallography, and compared with that of 1Cl · 3H2O. The structural feature for 2 is essentially consistent with that for 1, except for the absolute configurations around the octahedral Co(III) center. The optically active complex cation 2 exists as a monomer, accompanied by no intermolecular interactions in the π-electronic systems of bpy moieties. In the crystals of 3Cl · 7H2O, on the other hand, the enantiomeric complex cations, [Pt(bpy){Co(d-pen)2}]+ and [Pt(bpy){Co(l-pen)2}]+, are arranged alternately while overlapping the bpy planes along a axis, and the π electronic system of the bpy framework in [Pt(bpy){Co(d-pen)2}]+ interacts with those in [Pt(bpy){Co(l-pen)2}]+. Differences between the crystal structures of 2Cl · 3H2O and3Cl · 7H2O significantly reflect their diffuse reflectance spectra. In aqueous solution, each cation in both 2Cl · 3H2O and 3Cl · 7H2O is comparatively put on a free environment without such intermolecular interactions.