Homochiral helical coordination polymers constructed from achiral ligand of 5-(3-pyridyl)-isophthalic acid

Reactions of achiral 5-(3-pyridyl)-isophthalic acid (H2L) with Co2+ and Ni2+ under solvothermal conditions yield two new homochiral helical coordination polymers [Co(L) (H2O)2]n (1), [Ni(L) (H2O)2]n (2). Single crystal X-ray diffraction analyses show that complexes 1 and 2 are isomorphous with infinite 3D structures and they both contain two enantiomers, 1a and 1b for Co and 2a and 2b for Ni, crystallizing in the chiral hexagonal space groups P65 and P61, respectively. The enantiomeric nature of them is confirmed by the results of CD spectra. The optical properties of them were investigated in terms of diffuse reflectance, IR and fluorescent spectra, which both exhibit strong luminescence. The electronic band structure along with the density of states (DOS) calculated by the DFT method indicate that compound 1 pose an energy band gap of 3.58 eV and that the origin of the emission band may be mainly ascribed to charge transfer (ILCT) where the charges are transferred between the O-2p state and C-2p state.