LAUSR

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.