Cu(II) complexes of pyridine-2,6-dicarboxylate and N-donor neutral ligands: Synthesis, crystal structure, thermal behavior, DFT calculation and effect of aromatic compounds on their fluorescence

Two copper(II) complexes [Cu(pdc)(im)] (1) and {[Cu(pdc)(2-ap)(H2O)].2H2O} (2) [pdc, pyridine- 2,6-dicarboxylate; im, imidazole and 2-ap, 2-aminopyridine] have been synthesized and characterized by elemental analysis, IR spectroscopy, X-ray crystallography, and thermal analysis. Complexes 1 and 2 show a square planar and square pyramidal Cu(II) coordination sphere, respectively, and in solid state form hydrogen bonded 3D supramolecular networks. Both the complexes exhibit fluorescence in water– methanol solution at room temperature [kex = 261 nm, kem = 317 and 361 nm, quantum yield = 0.0149 for 1; kex = 278 nm, kem = 351 nm, quantum yield = 0.0031 for 2]. The effect of the presence of different aromatic compounds such as m-toluidine, aniline, nitrobenzene, p-cresol, phenol, etc., on the fluorescence of these copper complexes in solution has been inspected. Results indicate that complex 2 behaves as a fluorescence sensor for p-cresol, but loses its fluorescent properties in association with phenol. The optimized geometry from density functional theory (DFT) study shows a good agreement with the X-ray structural data. The electronic and IR spectra of these compounds are compared with results obtained by employing DFT and time-dependent density functional theory (TD-DFT) calculations.