A 3D Zn(II) Metal-Organic Framework Based on Citraconic Acid and 1,2-Bi(4-pyridyl)ethylene Mixed Ligands: Crystal Structure, Luminescence, and [2+2] Cycloaddition Reaction

A Zn(II) coordination polymer, {[Zn(ca)(bpe)]·0.5H 2 O} n (H 2 ca = citraconic acid, bpe = 1,2-bi(4-pyridyl)ethylene) has been prepared by hydrothermal reaction, and characterized by single-crystal X-ray diffraction, elemental analysis, FT IR, PXRD, and TGA. Title compound exhibits a three-dimensional metal-organic framework with lvt topology type and 4 2 ⋅8 4 Schläfli symbol. The compound has good phase purity and high thermal stability. The emission spectrum of the complex is similar to that of the powdered free bpe molecule, but the obvious red-shift may be due to the coordination of bpe with Zn ions, resulting in a reduced nonradiative decay of the intraligand excited state. The center-to-center olefin bond distance of bpe ligand in the compound, 3.620 Å, is suitable to undergo [2+2] cycloaddition reaction. The 1 H NMR spectrum of the cycloaddition product after UV irradiation for 24 h shows that the double bonds were partially photodimerized (82.6%) into the rctt -tpcb and rtct -tpcb derivatives.