Benign synthesis of the unsymmetrical ligand N-(8-quinolyl)quinoline-2-carboxamide (Hqcq) and the varied crystal chemistry of its Cu(II), Zn(II), and Cd(II) complexes bearing acetato and aqua co-ligands

A new benign and highly efficient procedure, with the ionic liquid tetrabutylammonium bromide as reaction medium, has been used for synthesis of the unsymmetrical ligand N-(8-quinolyl)quinoline-2-carboxamide. Three new complexes [Cu(qcq)(OAc)(H2O)], [Zn(qcq)(OAc)(H2O)], and [Cd(qcq)(OAc)(H2O)] were synthesized and characterized by elemental analysis, IR, UV-visible and H-1 NMR spectroscopy, and X-ray crystallography. The mono-anionic qcq(-) is a tridentate unsymmetrical ligand furnishing an N3 set, such that two N atoms of the two quinoline rings and one amido N atom occupy three meridional positions. In [Cd(qcq)(OAc)(H2O)] the acetate anion has a chelating bidentate coordination mode, whereas in [Cu(qcq)(OAc)(H2O)] and [Zn(qcq)(OAc)(H2O)] it acts as a terminal monodentate ligand. The coordination geometry around the M(II) ion is distorted square pyramid in the Cu complex, distorted trigonal bipyramid in the Zn complex, and distorted octahedron in the Cd complex. The discrete molecular units of these complexes are linked by hydrogen bonds and face-to-face pi-pi stacking interactions. The spectroscopic and electrochemical properties of these complexes are reported and discussed. .