Synthesis, characterization, and biological evaluation of Cu(II) complexes with the proton transfer salt of 2,6-pyridinedicarboxylic acid and 2-amino-4-methylpyridine

Abstract

A proton transfer compound, (Hamp)⁺(Hdipic)⁻ · 1.5H₂O (1), and Cu(II) complexes, [Cu(dipic)(amp)(H₂O)] · [Cu(dipic)(amp)] · H₂O · CH₃COOH (2) and [Cu(dipic)(amp)Cu(dipic)(amp)(H₂O)Cu(dipic)(amp)(H₂O)] · 3H₂O (3), have been synthesized from 2,6-pyridinedicarboxylic acid (H₂dipic) and 2-amino-4-methylpyridine (amp). They have been characterized by elemental, spectral (¹H-NMR, IR, and UV-Vis), and thermal analyses. In addition, magnetic measurements and single crystal X-ray diffraction have been applied to 2 and 3. The crystal structure of 2 consists of two independent and different cationic sites with Cu²⁺ ions. Cu1 is four-coordinate in a distorted square planar geometry and Cu2 is five-coordinate in a distorted square pyramid. Compound 3 has three independent and different cationic sites of Cu²⁺ ions. Cu1 is four-coordinate in a distorted square planar geometry and Cu2 and Cu3 have five-coordinate, distorted square-pyramidal sites. Inhibitory effects of 1, 2, and 3 have been studied and compared with starting compounds (amp and H₂dipic) on bacterial growth of Staphylococcus aureus and Escherichia coli cultures. Compounds 2 and 3 prevent bacterial growth although 1 has no effect. Compounds 2 and 3 are more effective than amp and H₂dipic, at similar concentrations on preventing bacterial growth for both organisms.

Keywords:

• Proton transfer
• Cu(II) complex
• Crystal structure
• Staphylococcus aureus
• Escherichia coli
• Bacterial growth

Acknowledgments

The authors gratefully acknowledge the support provided by Dumlupınar University, Turkey (under grant no. 2007/2 of the University Research Fund). The also thank the Faculty of Arts and Sciences, Ondokuz Mayis University, Turkey, for using the Stoe IPDS-2 diffractometer purchased under grant F.279 of the University Research Fund.