Synthesis, structures and properties of novel coordination polymers based on benzoate derivatives

Seven new transition metals coordination polymers based on 4,4′-bipyridine (4,4′-bipy) with meta-substituted benzoate derivatives namely 3-chlorobenzoate (3-Clbenz) and 3-nitrobenzoate (3-NO2benz) ligands have been successfully synthesized, such as {[Co3(4,4′-bipy)4(3-Clbenz)6(H2O)2]∙2CH3OH}n (1), {Ni(4,4′-bipy)(3-NO2benz)3}n (2), {Zn(4,4′-bipy)(3-NO2benz)2}n (3), {Cu(4,4′-bipy)0.5- (3-Clbenz)2]n (4), {Zn(4,4′-bipy)0.5(3-Clbenz)2}n (5), {Cu(4,4′-bipy)0.5(3-NO2benz)2}n (6) and {Zn(4,4′-bipy)0.5(3-NO2benz)2}n (7). All compounds, except the insufficient and unrepeatable compounds 2 and 7 have been fully characterized by using Fourier transform infrared (FT-IR) spectroscopy, elemental analysis (EA), solid state diffuse reflectance spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction (SCXRD) techniques. The crystal structures of these compounds display various types of topologies, 1D ladder chain-like structure for compound 1, 1D linear chain-like structure for compound 2, 1D zigzag chain-like structure for compound 3, 1D linear chain-like structure with paddle wheel units for compounds 4-7. The crystal structures of these compounds are further stabilized by weak interactions such as hydrogen bonding, C-H···π and π···π stacking interactions. For the investigation of their properties, the solid-state PL emission spectra of all measured compounds present the quenched intensities (λex 350 nm), revealing no photoluminescent properties in this CPs system. The PL sensing properties for small organic solvents of compounds 3 and 5 have been investigated. The results showed that the PL signals of compound 3 present the highest quenching emission for nitrobenzene. While that of compound 5 present the highest quenching emission for nitrobenzene and 2-propanol. The quenching emission of these compounds may be attributed to electron transition between the coordination structure and solvent guest molecules. Moreover, the expected gas adsorption properties of compounds 4-6 have been investigated. The results showed that compounds 4-6 are not exhibit adsorption with the gate-opening behavior because there is densely packing by C−H⋯π and π⋯π intermolecular interactions, resulting the less flexible in the crystal structures. Finally, the catalytic properties of Zn(II) compounds 3 and 5 have been performed in transesterification reaction of phenyl acetate/p-nitrophenyl acetate and methanol. The results show that compounds 3 and 5 present the good catalytic properties improving the yield of methyl acetate (MA) product in comparison to the control catalyst reaction.