Synthesis and structure of mononuclear copper(II) complexes with acyclic Schiff-base ligands containing organotellurium substituents: a comparative study with selenium analogs

Tellurium-bearing acyclic Schiff bases, 2,6-bis({N-2-(phenyltellurato)ethyl]}benzimidoyl)-4-methylphenol (HL³ ) and 2,6-bis({N-3-(phenyltellurato)propyl]}benzimidoyl)-4-methylphenol (HL⁴ ) of the Te₂N₂O type have been prepared by condensation of 4-methyl-2,6-dibenzoylphenol (mdbpH) with the appropriate phenyltellurato(alkyl)amine. HL³ and HL⁴ have been characterized by mass spectrometry, IR, electronic and ¹H-NMR spectroscopies and cyclic voltammetry. Their reactions with Cu(II) acetate monohydrate in a 2?:?1 molar ratio in methanol yield (C₆H₂(O)(Me){(C₆H₅)C=N(CH₂)_nTe(C₆H₅)}{(C₆H₅)C=O})₂Cu] (3 (n?=?2), 4 (n?=?3)) as suggested by analytical and spectroscopic data and single crystal X-ray crystallography of 3. In both complexes, one arm of the ligand undergoes hydrolysis at the C=N position and two molecules of the partially hydrolyzed ligand coordinate to Cu(II) through imido nitrogen and the phenolic oxygen. The telluriums do not form part of the copper(II) distorted square planar coordination sphere which has a trans-CuN₂O₂ core. Electrochemical studies of 3 and 4 indicate quasi-reversible reductions (E°′?=??1.113?V (3) and ?1.149?V (4)) corresponding to the reduction of copper(II) to copper(I). The interactions of 3 and 4 with calf thymus DNA, investigated by spectrophotometry and cyclic voltammetry, indicate that 3 and 4 bind to DNA via intercalation, and the binding affinity of 3 is lower than that of its selenium analog.