Thermodynamic studies on the addition of molecular oxygen to cobalt(II) complexes. Part 3. The cobalt(II)–tetraethylenepenta-amine–O2 system in aqueous solution at 25 °C

Abstract

Calorimetric measurements have been carried out on the heat evolved when O₂ is bubbled into KNO₃(0.1 mol dm^–3) aqueous solutions of Co(NO₃)₂, tetraethylenepenta-amine (tetren) and HCl, or when a Co(NO₃)₂ stock solution is added to a KNO₃(0.1 mol dm^–3) aqueous solution of tetren and HCl under both anaerobic (p_N2= 1 atm) or aerobic (p_O2= 1 atm) conditions. An acceptable agreement is found between the value for the enthalpy change of formation of [Co₂L₂O₂]⁴⁺(L = tetren) when it is obtained through direct measurements of oxygen addition to [CoL]²⁺ or by using the enthalpy changes relative to the formation of [CoL]²⁺ and [Co₂L₂O₂]⁴⁺ starting from Co²⁺. The thermodynamic data for the binding of oxygen to complexes of Co^II with tetren and other linear polyamines are compared and discussed.