Two pairs of Zn(II) coordination polymer enantiomers based on chiral aromatic polycarboxylate ligands: synthesis, crystal structures and properties

Two pairs of Zn-based chiral coordination polymers (CCPs), namely, [Zn((R)-cbca)center dot H2O], [Zn((S)-cbca)]center dot H2O], [Zn((R)-cna)center dot 2H(2)O] and [Zn((S)-cna)center dot H2O] {H(2)cbca = (R) or (S)-4'-(1-carboxyethoxy)-[1,1'-biphenyl]- 4-carboxylic acid, H(2)cna = (R) or (S)-6-(1-carboxyethoxy)-2-naphthoic acid} were synthesized under hydrothermal conditions. Their structures were determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, infrared spectroscopy, powder X-ray diffraction, circular dichroism (CD) spectroscopy. CCPs 1-4 crystallized in chiral space groups and the CD spectra demonstrate obvious positive or negative Cotton effects. Second-harmonic generation (SHG) measurements show that CCPs 1-4 are SHG active and the SHG efficiencies are 0.6, 0.6, 0.5 and 0.5 times as much as that of urea, respectively. CCPs 1-4 exhibit relatively high luminescence properties originating from ligand centered emission.