Cobalt complexes able to bind dioxygen: Thermodynamic studies and DFT calculations

The ligational properties of the ligand 2-[bis-(2-aminoethyl)-aminomethyl]phenol (L) towards Co(II) ion were studied by means of potentiometric measurements in aqueous solution (298.1 ± 0.1 K, I = 0.15 mol dm_3). L forms a stable mononuclear [CoH_1L]+ (logK = 13.42), a hydroxylated mononuclear [CoH_1LOH] and a dinuclear [(CoH_1L)2]2+ species in which the ligand/metal ratio is 2:2. The Co(II) species is prone to bind dioxygen forming a l-peroxo-l-hydroxo [(CoH_1L)2(lOH)(lO2)]+ dinuclear species. The stability constants of l-peroxo-l-hydroxo dinuclear and l-peroxo-mono-hydroxo species were analyzed in a series of open-chain polyamine and polyamino phenol ligands pointing out the role played by the ligand on the stability and the reversibility of the bound dioxygen. DFT calculations were carried out to predict the structure of the oxygenated Co(II)–dinuclear species for L and the related LI amino-phenol ligand. The crystal structure of the Co(III) species, derived from the oxydation of the Co(II)–oxygenated one, was also reported.