The preparation, characterization, and evaluation of a cobalt(III) complex [Inline graphic] with 13-membered tetraamide macrocyclic ligand (TAML) is described. This is a square-planar (X-ray) S = 1 paramagnetic (1H NMR) compound, which becomes an S = 0
diamagnetic octahedral species in excess d5-pyridine. Its one-electron oxidation at an electrode is fully reversible with the lowest E
½ value (0.66 V vs SCE) among all investigated CoIII TAML complexes. The oxidation results in a neutral
blue species which is consistent with a CoIII/radical-cation ligand. The ease of oxidation is likely due to the two benzene rings incorporated in the ligand structure (whereas there is just one in many other CoIII TAMLs). The oxidized neutral species are unexpectedly
EPR silent, presumably due to the π-stacking aggregation. However, they display eight-line hyperfine patterns in the presence of excess of 4-tert-butylpyridine or 4-tert-butyl isonitrile. The EPR spectra are more consistent with the CoIII/radical-cation ligand formulation
rather than with a CoIV complex. Attempts to synthesize a similar vanadium complex under the same conditions as for cobalt using [VVO(OCHMe2)3] were not successful. TAML-free decavanadate was isolated instead.
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Document Type: Research Article
Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, USA
Inorganic Chemistry, Department of Chemistry, Royal Institute of Technology, Stockholm, Sweden
Publication date: July 3, 2018