Synthesis, spectroscopic, thermal, and antimicrobial studies of tetradentate 12 and 14 member Schiff bases and their complexes with Fe(III), Co(II), and Cu(II)

Abstract

Two Schiff bases, L¹ (5,6;11,12-dibenzophenone-2,3,8,9-tetramethyl-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene) and L² (6,7;13,14-dibenzophenone-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclotetradeca-1,4,8,11-tetraene), bearing functionalized pendant arms have been synthesized by cyclocondensation of 3,4-diaminobenzophenone with 2,3-butanedione and 2,4-pentanedione, respectively. Mononuclear macrocyclic complexes [FeL¹Cl₂]Cl, [FeL²Cl₂]Cl, [ML¹Cl₂], and [ML²Cl₂] (where M = Co(II) and Cu(II)) have been prepared by reacting iron(III), cobalt(II), and copper(II) with the preformed Schiff base. The ligands and their corresponding metal complexes were characterized by elemental analyses, ESI-mass spectra, conductivity, magnetic moments, UV-Vis, EPR, IR, ¹H-, and ¹³C-NMR spectral studies, and TGA-DTA/DSC data. The TGA profiles exhibit a two-step pyrolysis, although the iron complexes decompose in three steps, leaving behind metal oxides as the final product. The ligands and complexes were screened in vitro against Gram-positive bacteria, Gram-negative bacteria, and fungi.

Keywords:

• Antimicrobial studies
• Pendant arm
• Physico-chemical studies
• Schiff-base ligands
• Thermal studies

Acknowledgments

The authors acknowledge The Chairman, Department of Chemistry, Aligarh Muslim University, Aligarh, India for providing necessary research facilities. They are grateful to Dr Asad Ullah Khan, Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh for performing antimicrobial activity and SAIF, Panjab University Chandigarh, India for providing, NMR and elemental analysis, and to SAIF IIT-Madras, Chennai, India for performing EPR spectra. They thank Prof. R.J. Singh, Department of Physics, AMU, Aligarh for the discussion of EPR spectra.