Stereoselective association of ferrocene-contained molecular clips in coordination polymers

Abstract

The assembly of racemic molecular clipsSS- and RR- 1,1'-bis(1-(1,2,4-triazol-1-yl)ethyl)ferrocene (FcTz) into coordination polymers has been studied systematically. Stereoselective homochiral association of Zn(CH₃COO)₂·4 H₂O leads to the formation of one-dimensional helical chains having a right handed enantiomer 1 and a left-handed enantiomer 1′ viaself-assembly. The CD spectra of crystals of 1 and 1′ exhibit the opposite Cotton responses and suggest that two enantiomers of the molecular clips are resolved by the metal-induced crystallization. On the other hand, the meso type association of CdI₂ results in the formation of centro-symmetric two-dimensional sheets. It is shown that the product of the homochiral association is predominately formed when the metal center is tetrahedrally coordinated, and that of the meso-association is generated at the time the metal centers is sited in a mirror symmetric tetragonal pyramidal geometry. The weak but significant intermolecular interactions are also found to be essential in controlling the homochiral aggregation of these helical polymers and achiral sheets.