Stereospecific π–π stacking interactions between pseudo-enantiomeric sulfur-bridged dinuclear Co(III)–Pd(II) and Co(III)–Pt(II) complexes of optically active penicillaminates

Abstract

The reactions of trans(N)-[Co(d-pen)2]− (pen=penicillaminate) with [MCl2(bpy)] (M=Pd or Pt, bpy=2,2′-bipyridine) and trans(N)-[Co(l-pen)2]− with [M′Cl2(bpy)] (M′=Pd or Pt) stereoselectively gave optically active S-bridged dinuclear complexes, [M(bpy){Co(d-pen)2}]+ and [M′(bpy){Co(l-pen)2}]+, respectively. Assemblies between these pseudo-enantiomers with different d8 metal centers, [M(bpy){Co(d-pen)}2]+ and [M′(bpy){Co(l-pen)}2]+ (M′≠M), have been examined from stereo- and spectrochemical aspects. As a result, a mixture of equimolar amounts of optically active sulfur-bridged dinuclear complex, [M(bpy){Co(d-pen)}2]Cl·3H2O, and its pseudo-enantiomer, [M′(bpy){Co(l-pen)}2]Cl·3H2O, in H2O crystallizes as [M(bpy){Co(d-pen)}2][M′(bpy){Co(l-pen)}2]Cl·14H2O, in which two complex cations with heterometallic square-planar units form a 1:1 π–π stacked unit. The 1:1 π–π stacked unit between pseudo-enantiomeric complex cations develops into a linear-chain with further π–π stacking contacts. These structural characteristics reflect their solid-state spectral behaviors.