Abstract
Three mononuclear CoIII complexes, [Co(L1 tBu)(bdbp)]·2EtOH (1), [Co(L2 tBu)(bdbp)] (2), and [Co(L3 tBu)2]ClO4 (3) (where H2L1 tBu = bis[{6-benzoyl-4-tert-butyl-2-hydroxyphenyl}benzi-midoyl]-1,2-ethane, H2L2 tBu = bis[{6-benzoyl-4-tert-butyl-2-hydroxyphenyl}benzimidoyl]-1,3-propane, bdbpH = 4-tert-butyl-2,6-dibenzoylphenol and HL3 tBu = 2-{N-(4-amino-butyl)benzimidoyl}-6-benzoyl-4-tert-butylphenol), have been synthesized by one-pot condensation involving CoII perchlorate, ethane-1,2-diamine, propane-1,3-diamine, and butane-1,4-diamine. The Schiff bases, H2L2 and HL3, and 1–3 have been characterized by elemental analyses, conductivity measurements, mass spectrometry, IR, electronic, 1H and 13C NMR spectroscopy, cyclic voltammetry, and X-ray crystallography. In 1 and 2, the tetradentate ONNO ligand wraps around cobalt in a rare β cis-conformation. Complex 3 possesses a tridentate NNO ligand leading to two seven-membered chelate rings in a fac-CoN4O2 octahedral configuration. Density functional theory (DFT) calculations provide a satisfactory description of the electronic properties of the new compounds. All the complexes are redox active and display the Co(III)–Co(II) couple in the potential range −0.6– + 0.3 V (vs. Ag/AgNO3). Interaction of the complexes with calf thymus DNA (CT-DNA) has been investigated by a spectrophotometric method and cyclic voltammetry. Based on these observations, an intercalative binding mode of DNA has been proposed. The order of their intrinsic DNA binding constants Kb is Kb (1) < Kb (2) < Kb (3). The observed trend in the binding constant values is consistent with the energy gap between the HOMO and LUMO molecular orbitals.
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Acknowledgements
We thank Mr. V. Ramkumar (Department of Chemistry, IIT Madras) for assistance with the data collection and the XRD facility, Dr. J.D. Smith, University of Sussex, UK and Prof. Pavan Mathur, University of Delhi for discussion and referees for their constructive comments.