A fourfold interpenetrating cadmium(II) metal-organic framework based on 2,4,6-tris(pyridin-4-yl)-1,3,5-triazine with reversible photochromic properties.

Abstract

2,4,6-Tris(pyridin-4-yl)-1,3,5-triazine (tpt), as an organic molecule with an electron-deficient nature, has attracted considerable interest because of its photoinduced electron transfer from neutral organic molecules to form stable anionic radicals. This makes it an excellent candidate as an organic linker in the construction of photochromic complexes. Such a photochromic three-dimensional (3D) metal-organic framework (MOF) has been prepared using this ligand. Crystallization of tpt with Cd(NO3)2·4H2O in an N,N-dimethylacetamide-methanol mixed-solvent system under solvothermal conditions afforded the 3D MOF poly[[bis(nitrato-κ2O,O')cadmium(II)]-μ3-2,4,6-tris(pyridin-4-yl)-1,3,5-triazine-κ3N2:N4:N6], [Cd(NO3)2(C18H12N6)]n, which was characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis and single-crystal X-ray diffraction. The X-ray diffraction crystal structure analysis reveals that the asymmetric unit contains one independent CdII cation, one tpt ligand and two coordinated NO3- anions. The CdII cations are connected by tpt ligands to generate a 3D framework. The single framework leaves voids that are filled by mutual interpenetration of three independent equivalent frameworks in a fourfold interpenetrating architecture. The compound shows a good thermal stability and exhibits a reversible photochromic behaviour, which may originate from the photoinduced electron-transfer generation of radicals in the tpt ligand.