Synthesis and characterization of cobalt(<scp>III</scp>) and cobalt(<scp>IV</scp>) complexes of N-(2-hydroxyphenyl)salicylamide and homologues

Abstract

Tridentate trianionic chelating ligands, N-(2-hydroxyphenyl)salicylamide (H3L1) and its homologues with a substituent on the 2-hydroxyphenyl moiety (5-Me, H3L2; 5-Cl, H3L3; 4-NO2, H3L4; 5-NO2, H3L5), were utilized for the synthesis of cobalt complexes. The ligands H3L1 and H3L2 gave uncharacterized substances when treated with a cobalt(II) salt, whereas H3L3—H3L5 formed cobalt(III) complexes of general formula K3[CoL2.] The cobalt(III) complexes were characterized by elemental analyses, thermogravimetric analyses, electronic spectra, and cyclic voltammograms. Cyclic voltammograms showed two redox couples at significantly low potential, which were assigned to the CoIV–CoIII and CoV–CoIV redox processes based on controlled-potential electrolysis and e.s.r. investigations. The cobalt(III) complexes were readily oxidized chemically (with I2,) or electrochemically to the cobalt(IV) complexes, which were identified by an e.s.r. signal near g= 2.0 with an eight-line hyperfine structure (Aav.= 0.001 92 cm–1).