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Keywords:

  • Helical structures;
  • Metal–organic frameworks;
  • Luminescence;
  • Magnetic properties

Abstract

Four new helical metal–organic frameworks (MOFs), namely [ZnL(bpp)]n·4nH2O {1, H2L = 3-[4-(carboxymethoxy)phenyl]propanoic acid, bpp = 1,3-di-4-pyridylpropane}, [CdL(bpp)]n (2), [CoL(bpp)(H2O)0.5]n (3), and [NiL(bpp)(H2O)0.5]n (4), have been synthesized and characterized. X-ray crystallographic analyses show that 1 exhibits a 3D supramolecular framework, which is composed of 2D layers further linked by π–π stacking interactions. Compound 2 displays a 2D framework structure consisting of (Cd–L)n and (Cd–bpp)n double helices with right- or left-handed helical chains, in which the right- and left-handed homochiral layers are alternatively arrayed though π–π stacking interactions to finally form a racemic 3D structure. Compound 3 features a 3D architecture with right- and left-handed helical chains, in which 1D (Co–bpp)n and 2D (Co–L)n achiral layers are observed. The structure of 4 is very similar to that of 3, and its most notable characteristic is the tetraflexural [Ni–L]n helical chains in the [010] plane. Compounds 1 and 2 exhibit strong violet and blue photoluminescence emissions, respectively. The magnetic properties for 3 and 4 have been investigated at 2–300 K, and they exhibit antiferromagnetic and ferromagnetic interactions, respectively.