Architectures of transition metal(ii) polymeric frameworks constructed from 3- fluorophthalic acid and 1,3-bis(4-pyridyl)propane: synthesis, crystal structures and properties

Abstract

Reactions of transition metal(II) salts with a rigid 3-fluorophthalic acid (H₂Fpht) and a flexible ligand, 1,3-bis(4-pyridyl)propane (bpp), afforded a series of coordination polymers, [Cu(Fpht)bpp]·0.5H₂O (1), [Cu(Fpht)bpp·H₂O] (2), [Cd(Fpht)bpp·H₂O]·H₂O (3), [Co(Fpht)bpp·H₂O] (4) and [Ni(Fpht)bpp·H₂O] (5). The five complexes were characterized by single crystal X-ray diffraction. 1 and 2 were obtained from a one-pot reaction. 1 possesses a very rare achiral 6⁶ self-catenated layer topology with a {CuO₃N₂} square-pyramidal coordination geometry; whereas 2 exhibits a chiral 3D 6⁵.8 topology framework with two crystallographically different copper sites, {CuO₄N₂} octahedral and {CuO₃N₂} square pyramidal coordination fashions. 3 contains two rare types of double-stranded helices, based on {CdO₅N₂} pentagonal bipyramidal and {CdO₄N₂} octahedral coordination fashions. Complexes 4 and 5 are isostructural 3D coordination polymers and are built from right-/left-handed M-Fpht helices and bpp linkers and they possess a 6⁵.8 topology. The results show that metal(II) complexes composed of H₂Fpht and bpp ligands exhibit diverse MOF structures depending on the geometric requirement of the metal(II) ions. Complex 5 exhibits ferroelectric and SHG properties, while 4 shows a ferroelectric feature. The fluorescence of the five complexes comes from the π^*–π transition of the ligands.