Formation of 1-D ladder- and 2-D sheet-like networks due to stereospecific π–π stacking and hydrogen bonding between enantiomeric sulfur-bridged dinuclear complexes of penicillaminates

Abstract

Reaction of trans(N)-[Co(D-pen)2]− (pen = penicillaminate) or trans(N)-[Co(L-pen)2]− with [MCl2(L)] {M = Pd or Pt, L = 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen)} in the presence of tetrafluoroborate stereoselectively gave an optically active S-bridged dinuclear complex, [M(L){Co(D-pen)2}]BF4 · 2H2O or [M(L){Co(L-pen)2}]BF4 · 2H2O. The mixture of equimolar amounts of these enantiomers in H2O crystallizes as [M(L){Co(D-pen)2}]0.5[M(L){Co(L-pen)2}]0.5BF4 · 4H2O (DLbpyM · 4H2O, DLphenM-A · 4H2O), in which the enantiomeric complex cations are included by the ratio of 1 : 1. In crystals of DLbpyM · 4H2O and DLphenM-A · 4H2O, [M(L){Co(D-pen)2}]+ and [M(L){Co(L-pen)2}]+ interact stereospecifically with each other through π-conjugated systems to form dimeric structures. Other racemic crystals with the same chemical compositions as DLphenM-A · 4H2O, DLphenM-B · 4H2O, were obtained from equimolar amounts of [M(phen){Co(D-pen)2}]+ and [M(phen){Co(L-pen)2}]+ in aqueous acetonitrile solution. In the crystals of DLphenM-B · 4H2O, [M(phen){Co(D-pen)2}]+ and [M(phen){Co(L-pen)2}]+ are arranged alternately while overlapping phen planes, and the π electronic systems of phen interact with each other. Although stereospecific hydrogen bonds between the coordinated −NH2 and −COO− groups are formed in both DLphenM-A · 4H2O and DLphenM-B · 4H2O, their bonding modes differ noticeably from each other. As a result, DLphenM-A · 4H2O builds up 1-D ladder-like networks due to the stereospecific π–π stackings and hydrogen bondings between enantiomers, while 2-D sheet-like networks are established for DLphenM-B · 4H2O.