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

The synthesis and characterization of specific - and -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 -isomer under ambient reaction conditions. Whereas a reaction using cobalt(II) nitrate provided only the -isomer when the reaction was continued for a prolonged time. On the other hand, the -isomer was converted to the -isomer in solution upon treatment with chloride ions. The chloride-assisted formation of the -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 -isomer in different solvents was investigated, and solvent-dependent aggregation and a solvent-dependent Cotton effect were observed.