Benign synthesis of the unsymmetrical ligand N-(quinolin-8-yl)pyrazine-2-carboxamide. Preparation, electrochemistry, antibacterial activity, and crystal structures of Cu(II) and Zn(II) complexes

Abstract

Hqpzc has been synthesized by a highly efficient procedure using the ionic liquid TBAB as an environmentally benign reaction medium. [Cu(qpzc)(OAc)]·H₂O (1) and [Zn(qpzc)(OAc)(H₂O)] (2), complexes of the deprotonated ligand, qpzc¯ [qpzc¯ = N-(quinolin-8-yl)pyrazine-2-carboxamide], have been synthesized and characterized by elemental analyses, spectroscopic methods, and X-ray crystallography. The coordination geometry around the metal ions in both complexes is distorted square pyramidal. The mono-anionic qpzc¯ is a tridentate unsymmetrical ligand furnishing an N3 set, occupying three of the four basal positions. Acetate is a bidentate ligand in 1 and unidentate in 2. The apical position in 2 is occupied by water. Quite strong O-H…O hydrogen bonds create columns of complexes [rod group p21(11)] in the copper complex, but in conjunction with π-π interactions, a 3D edifice in the zinc complex. The electrochemical behavior of the ligand and its copper and zinc complexes shows that the quinoline ring reduces at more positive potentials in these complexes relative to the free ligand. The in vitro antibacterial activities of these complexes were tested against Escherichia Coli and Staphylococcus Aureus.

Keywords:

• Cu(II)
• Zn(II) carboxamide complexes
• Crystal structure
• Cyclic voltammetry
• Antibacterial

Acknowledgements

Partial support of this work by the Isfahan University of Technology Research Council is gratefully acknowledged.