Preparation, structure and luminescent characterization of a series of metal–organic frameworks based on flexible ligands with nitrogen heterocycles and carboxyl

Seven new compounds, [Zn(pypymba)2]n(1), [Co(pypymba)2]n(2), [Cd(pypymba)2]n(3), [Cd(Hpypymba)Cl2]n(4), {[Cd(pypymba)Cl]·C2H5OH·H2O}n(5), [Cd(pypyaa)Cl]n(6), {[Cd2(pyznpy)2Cl2H2O]·H2O}n(7) [Hpypymba = 4-((3-(pyrazin-2-yl)-1H-pyrazol-1-yl)methyl)benzoic acid, Hpyznpy = 4-((3-(pyridin-2-yl)-1H-pyrazol-1-yl)methyl)benzoic acid, Hpypyaa = 2-(3-pyridin-2-yl)-1H-pyrazol-1-yl)acetic acid], were hydrothermally synthesized by tuning the metal ion's species, counter anions, solvents and pH values and characterized by routine methods: XRD, elemental analysis, fluorescence properties analysis, TGA and crystal structure analysis and single-crystal X-ray crystallography. The main structures of the compounds 1, 2, and 3 are extended to similar 3D structures by C–H…N, C–H…O hydrogen bonds and π…π stacking under the same synthesis method. Each Cd(II) node of compound 4 has four chlorine bridges (two pairs of double chlorine); Each Cd(II) node of compounds 5, 6 has two chlorine bridges (a pair of double chlorine bridges), while their spatial structures are expanded in different ways. Compound 7 also contains chlorine atoms, but does not contain chlorine bridged structures. The luminescent properties of compound 7 and the ones immersed in various kinds of organic compounds and [email protected] solutions have been investigated. Importantly, 7 shows highly sensitive response to nitrobenzene and Fe3+ through luminescence quenching effects, making it a promising luminescent sensor for nitrobenzene and Fe3+.