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 [λex = 261 nm, λem = 317 and 361 nm, quantum yield = 0.0149 for 1; λex = 278 nm, λem = 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.