Luminescent materials based on N-(3-nitrophenyl)-N'-(4-R-C₆H₄)oxamato zincate(II) complexes

A series of N-(3-NO2-C6H4)-N'-(4-R-C6H4)oxamato zincate(II) complexes (3a, R = OMe; 3b, R = Me; 3c, R=H; 3d, R=F; 3e, R = Cl; 3f, R = Br; 3 g, R = NO2) was synthesized by the treatment of N-(3-nitrophenyl)-N'-(4-R-C6H4)oxamides (2a g) with [Zn(OAc)(2)(H2O)(2)] in a 2:1 molar ratio in the presence of four equivalents of [(n)Bu4N] OH to study the influence of electron-withdrawing and electron-donating groups R on the electronic properties of 3a g. The structures of 3c,f in the solid state were determined by single crystal X-ray structure analysis confirming the tetrahedral environment around Zn(II) set-up by the respective oxamato ligands. The calculated electrostatic potentials of 3f rationalize the formation of C-H center dot center dot center dot Br-C and C-Br center dot center dot center dot p contacts resulting in the formation of a chain structure. Complexes 3a-g show characteristic LLCT ( pi -> pi*) bands in their UV-Vis spectra, which were additionally confirmed by TD-DFT calculations. DFT calculations confirm that the Zn(II) orbitals neither contribute to the HOMO nor LUMO orbitals, since they are mainly localized on the ligands. The thermal decomposition behavior of 3a g was performed by thermogravimetric analysis and differential scanning calorimetry and the results showed that the complexes are thermally stable. Strong photoluminescence was observed in complexes 3a g at ambient temperature both in solid state and in solution and the complexes making them good candidates for potential luminescent materials.