First one-dimensional homochiral stairway-like Cu(ii) chains: crystal structures, circular dichroism (CD) spectra, ferroelectricity and antiferromagnetic properties

Abstract

The reactions of enantiopure chiral ligands (+)/(−)-4,5-pinenepyridyl-2-pyrazine (L_S/L_R) with CuCl₂·2H₂O in CH₃OH/CH₂Cl₂ solution led to the formations of one-dimensional homochiral enantiomeric pairs with the formula [Cu(L_R/S)Cl₂]n·2H₂O (R-1 and S-1, the isomers containing the L_R and L_S ligands, respectively). The circular dichroism (CD) spectra verified their chiroptical activities and enantiomeric natures. Their structures have been determined by X-ray single-crystal analyses, showing stairway-like and mirror-symmetric features, which represent the first examples of homochiral metal complexes with stairway-like structures. The ferroelectric property measurement indicated that R-1 exhibits ferroelectricity with the remnant polarization (P_r) value of 0.02 μC cm⁻² under an applied electric field of 6.1 kV cm⁻¹ at room temperature. The magnetic investigation of R-1 showed a weak intrachain antiferromagnetic coupling between Cu(II)–Cu(II) ions mediated by pyrazine, which can be interpreted by a spin-polarization mechanism. All these results suggested that R-1 and S-1 are potential multifunctional molecule-based materials combining optical activity, ferroelectricity and magnetism within one molecule.