Preparation, structural, spectroscopic, thermal and DFT characterization of cadmium(II) complexes with quinaldic acid

Cadmium(II) complex with quinaldic acid (quinH), [Cd(quin)2(H2O)2] (1), was prepared by the reaction of cadmium(II) acetate and quinaldic acid in water–ethanol mixture, while another cadmium(II) complex, [Cd(quin)2(DMSO)2] (2), was prepared by the recrystallization of 1 in DMSO. Both complexes were characterized by IR spectroscopy and TGA/DTA methods. The crystal structure of 2 was determined by X-ray structure diffraction analysis. Cadmium(II) ion is octahedrally coordinated by two N,O-bidentate quinaldate ligands in equatorial and by two DMSO molecules in axial positions. Only weak intermolecular C–H···O hydrogen bonds and π–π stacking interactions as packing forces are present in the crystal structure of 2. The theoretical investigations included geometry optimizations of both complexes at DFT level (B3LYP and mPW1PW91 functionals) and calculations of vibrational frequencies. Calculated and experimental IR spectra were compared and characteristic bands assigned. The electronic properties of the complexes were investigated by the NBO analysis. Thermogravimetric studies showed the initial loss of two coordinated water molecules in 1 and of DMSO in 2 and then complete decomposition of quinaldate ligands for both 1 and 2.

Two cadmium(II) complexes, [Cd(quin)2(H2O)2] (1) and [Cd(quin)2(DMSO)2] (2) were prepared and the crystal structure of 2 revealed by X-ray structural analysis. The structures of 1 and 2 were optimized and their calculated vibrational frequencies compared with the experimental IR spectra. The electronic properties of 1 and 2 were analyzed by NBO analysis resulting with additional insights about donor–acceptor interactions.Figure optionsDownload as PowerPoint slideHighlights
► CdII complexes [Cd(quin)2(H2O)2] (1) and [Cd(quin)2(DMSO)2] (2) prepared.
► Characterization by spectroscopic and thermal methods; X-ray crystal structure of 2.
► CdII ion octahedrally coordinated by two quinaldate ligands and two DMSO molecules.
► DFT calculations on monomer units of 1 and 2 and comparison with experimental data.
► NBO analysis for additional insights about donor–acceptor interactions in complexes.