Synthesis and characterization of cis and trans cobalt(ii) nalidixate complexes having a 1-(4-chlorophenyl)-3-(pyridin-4-ylmethyl)urea ligand

Abstract

The synthesis and characterization of specific cis- and trans-isomers of a cobalt(II) bis-nalidixate complex with a pyridine-based urea, 1-(4-chlorophenyl)-3-(pyridin-4-ylmethyl)urea (L), ligand are reported. The two isomers, cis-[Co(L)₂(NALD)₂]·0.5DMF·H₂O and trans-[Co(L)₂(NALD)₂]·2DMF·2H₂O (the nalidixate anion is abbreviated to NALD) were prepared by anion-guided synthesis. When cobalt(II) chloride was used as one of the reactants, the reaction yielded the trans-isomer under ambient reaction conditions. Whereas a reaction using cobalt(II) nitrate provided only the cis-isomer when the reaction was continued for a prolonged time. On the other hand, the cis-isomer was converted to the trans-isomer in solution upon treatment with chloride ions. The chloride-assisted formation of the trans-isomer was investigated by a UV-visible study, and it passed through a bond reorganization by forming a tetrahedral intermediate complex. A DFT calculation was carried out to show the difference in energy between the isomers as well as the energy of a plausible tetrahedral cobalt complex. The aggregation behavior of the cis-isomer in different solvents was investigated, and solvent-dependent aggregation and a solvent-dependent Cotton effect were observed.