Through spectrophotometric and potentiometric measurements it has been verified that in aerated aqueous solutions of CoII containing tris(2-aminoethyl)amine (tren) as ligand, the doubly bridged μ-peroxo-μ-hydroxo dicobalt ion [Co2L2(O2)(OH)]3+ (L = tren) is totally formed at pH > 6.5. In aerated aqueous solutions of CoII and 3,7-diazanonane-1,9-diamine (dadn) at pH 6.5 only the singly bridged μ-peroxo dicobalt ion [Co2L2(O2)]4+ (L = dadn) is present. This complex at higher pH adds OH- ions in its axial positions; at pH > 10.5 the singly bridged μ-peroxo-dihydroxo dicobalt ion [Co2L2(O2)(OH)2]2+ is totally formed. The singly bridged complex [Co2L2(O2)]4+, after several hours, converts irreversibly into the doubly bridged μ-peroxo-μ-hydroxo ion [Co2L2(O2)(OH)]3+, while the single bridged [Co2L2(O2)(OH)2]2+ ion slowly autoxidizes to CoIII. By means of calorimetric measurements, usually carried out at constant pH, the enthalpies of formation of [Co2L2(O2)]4+ and [Co2L2(O2)(OH)2]2+ (L = dadn) and [Co2L2(O2)(OH)]3+ (L = tren) have been obtained. These results are compared with the enthalpies relative to the oxygen addition to [Co(trien)]2+ ion (trien = triethylenetetra-amine), and the enthalpy effects, connected with the change from a linear amine (trien) to its branched isomer (tren) and from the sequence 5,5,5 (trien) to the sequence 5,6,5 (dadn) of the chelate rings, are discussed.

Calorimetric Study on Oxygen Addition to Cobalt(II) Complexes with Tris-(2-aminoethyl)amine and 3,7-Diazanonane-1,9-diamine

CABANI, SERGIO;CECCANTI, NORBERTO;TINE', MARIA ROSARIA
1988

Abstract

Through spectrophotometric and potentiometric measurements it has been verified that in aerated aqueous solutions of CoII containing tris(2-aminoethyl)amine (tren) as ligand, the doubly bridged μ-peroxo-μ-hydroxo dicobalt ion [Co2L2(O2)(OH)]3+ (L = tren) is totally formed at pH > 6.5. In aerated aqueous solutions of CoII and 3,7-diazanonane-1,9-diamine (dadn) at pH 6.5 only the singly bridged μ-peroxo dicobalt ion [Co2L2(O2)]4+ (L = dadn) is present. This complex at higher pH adds OH- ions in its axial positions; at pH > 10.5 the singly bridged μ-peroxo-dihydroxo dicobalt ion [Co2L2(O2)(OH)2]2+ is totally formed. The singly bridged complex [Co2L2(O2)]4+, after several hours, converts irreversibly into the doubly bridged μ-peroxo-μ-hydroxo ion [Co2L2(O2)(OH)]3+, while the single bridged [Co2L2(O2)(OH)2]2+ ion slowly autoxidizes to CoIII. By means of calorimetric measurements, usually carried out at constant pH, the enthalpies of formation of [Co2L2(O2)]4+ and [Co2L2(O2)(OH)2]2+ (L = dadn) and [Co2L2(O2)(OH)]3+ (L = tren) have been obtained. These results are compared with the enthalpies relative to the oxygen addition to [Co(trien)]2+ ion (trien = triethylenetetra-amine), and the enthalpy effects, connected with the change from a linear amine (trien) to its branched isomer (tren) and from the sequence 5,5,5 (trien) to the sequence 5,6,5 (dadn) of the chelate rings, are discussed.
Cabani, Sergio; Ceccanti, Norberto; Tine', MARIA ROSARIA
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/11555
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