Norberto Ceccanti

Isothermal vapour/liquid equilibria of binary mixtures with dibutyl ether at 298.15 K

A head-space gas chromatographic technique has been used to determine vapour/liquid equilibria at 298.15 K of binary mixtures of di-n-butyl ether plus an organic compound (hexane, octane, diethyl ether, tetrahydrofuran, propylamine, butylamine, propanone, cyclopentanone, methanol, butan-1-ol, acetonitrile). Excess molar Gibbs energies, GE, for the systems investigated have been obtained by a least-squares treatment of equilibrium data. Mixtures with hexane, octane and diethyl ether revealed an almost ideal behaviour. Other systems showed positive deviations, which increase with the polarity of the second component. Dibutyl ether + butanol and + cyclopentanone revealed the formation of azeotropic compositions. The Kirkwood–Buff integrals over the entire composition range have been calculated from the composition dependence of GE, and briefly discussed.

Thermodynamic and kinetic aspects of the binding reaction of molecular oxygen on Co(II) complexes in aqueous solutions

A short survey is given of the main characteristics of the reaction of uptake of molecular oxygen by biological dioxygen carriers. Co(ll) complexes able to bind dioxygen are then examined in order to determine whether the type and features of the peroxocomplexes formed are related to the nature of the ligand and the solvent. The thermodynamic and kinetic data relative to the formation in aqueous solution of peroxocompounds starting from Co(ll) complexes with ligands belonging to three families (open-chain, macrocyclic and macropolytopic) of saturated polyamines are also examined in greater detail.

Thermodynamic study of organic compounds in di-n-butyl ether. Enthalpy and Gibbs energy of solvation

The Gibbs energies and enthalpies of solvation of some hydrocarbons (n-hexane, n-octane, cyclohexane), alcohols (methanol, propan-1-ol, butan-1-ol, butan-2-ol), ethers (diethyl ether, tetrahydrofuran), ketones (propanone, pentan-3-one, cyclopentanone), amines (n-propylamine, n-butylamine), and acetonitrile in di-n-butyl ether have been determined at 298.15 K from vapour–liquid equilibrium measurements and from limiting enthalpies of solution. The data obtained have been compared with the corresponding values of the solvation functions in octan-1-ol and hexadecane. The phenomenology has been discussed in terms of a simple group additivity scheme. The interaction effects of polar and non-polar groups with the solvents have been deduced from the above group contributions combined with the cavity terms estimated through the scaled particle theory. The linear solvation energy relationships (LSER) have also been used for correlating the thermodynamic solvation function to the structural features of the solutes. All the approaches consistently highlight that the hydrophobic groups exhibit interactions with the solvent of nearly the same strength in the three media, while clearly different interactions are shown by polar groups.

Thermodynamics and kinetics of dioxygen binding to Co(II) complexes with saturated macrocyclic tetraamines

Some thermodynamic and kinetic aspects of the reactions of dioxygen binding to Co(II) complexes with the two cyclic tetraamines 1,4,7,10-tetraazacyclododecane ([12]aneN4) and 1,4,8,11-tetraazacyclotridecane ([13]aneN4) are examined. Specifically, results are reported on: (1) the determination of the protonation constants and protonation enthalpies for both [12]aneN4 and [13]aneN4 ligands; (2) the study of the kinetics of the formation of the precursor CoL complexes for L=[12]aneN4 and [13]aneN4 carried out by monitoring the uptake rate of molecular dioxygen; (3) the recognition of the type of dioxygen adducts formed at various pH values; (4) the determination of the kinetic and thermodynamic data characterising the reactions of isomerization of monobridged μ-peroxo-monohydroxo (CoL)2(μ-O2)(OH) complexes into the dibridged μ-peroxo-μ-hydroxo (CoL)2(μ-O2)(μ-OH) complexes, and the reactions of conversion of the dibridged μ-peroxo-μ-hydroxo (CoL)2(μ-O2)(μ-OH) complexes into the monobridged μ-peroxo-dihydroxo (CoL)2(μ-O2)(OH)2 complexes.

Cobalt(II) dioxygen carriers based on dinucleating ligands: Part 2. Kinetics of dioxygen binding

Abstract We consider here the kinetics of the reaction of formation of dioxygenated Co(II) complexes with the binucleating ligands 1,23-bis(methylamino)-3,6,9,12,15,18,21-heptaazatricosane (Me2Octaen), 1,4,7,10,13,16,19,22,25-nonaazacycloheptacosane ([27]aneN9), 1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane ([30]aneN10), and 1,4,7,10,13,16,19,22,25,28,31-undecaazacyclotritriacontane ([33]aneN11). The most important result is that the Co(II) complexes with these polyamines in aqueous solution and at room temperature are very flexible in binding dioxygen: by changing the value of the ligand to cobalt concentration ratio ( R= C L 0 C Co 0 ) and the pH of the solution, it is possible to modulate the dioxygen uptake obtaining two-to-one or one-to-one, Co/O2 superoxo complexes. As to the kinetics of the formation of these complexes, we find that the rate-determining step is the transformation of a cobalt-ligand precursor complex, inert towards dioxygen, to yield an active form, whereas the reaction of dioxygen uptake is fast in all the investigated systems.

Cobalt(II) dioxygen carriers based on dinucleating ligands.: Part 1. Thermodynamics of dioxygen binding in aqueous solution

The equilibria involving the uptake of dioxygen (O2) to the dicobalt(II) complexes of the macrocyclic ligands [27]aneN9 (1,4,7,10,13,16,19,22,25-nonaazacycloheptacosane) and [30]aneN10 (1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane), and of the acyclic polyamine Me2octaen (1,25-dimethyl-1,4,7,10,13,16,19,22,25-nonaazapentacosane) have been studied by potentiometric measurements in 0.15 mol dm−3 NaClO4 aqueous solution at 298.1±0.1 K, and the relevant equilibrium constants have been reported. All three ligands form stable oxygenated complexes of the type [Co2L(O2)]4+ and [Co2L(O2)OH]3+, in which the O2 molecule is bound in the end-on mode to a single metal ion. In the case of the macrocyclic complexes the coordination of O2 and OH− reveals a cooperativity effect, i.e. a significant stability increase is observed when one of these species coordinates to a dinuclear complex containing the other one, with respect to the same reactions involving (Co2L)4+. This behaviour suggests the interaction via hydrogen bonding between the two species (O2 and OH−) coordinated to different cobalt(II) ions.

Cascade complex formation by phosphate in the cobalt(II)/[30]aneN10 anaerobic system

Abstract The interaction of phosphate with the mono- and binuclear cobalt(II) complexes of [30]aneN 10 (1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane) has been studied by potentiometry in 0.15 mol dm −3 NaClO 4 solution at 298.15 K under anaerobic conditions. The stable species [CoH 2 ([30]aneN 10 )PO 4 ] + , [CoH 4 ([30]aneN 10 )PO 4 ] 3+ , [Co 2 H([30]aneN 10 )PO 4 ] 2+ , [Co 2 H 2 ([30]aneN 10 )PO 4 ] 3+ and [Co 2 H 3 ([30]aneN 10 )PO 4 ] 4+ , where the phosphate anion is directly bound to the metal ions or acts as a second sphere ligand, are formed and their stability constants have been determined. The results obtained allowed for the selection of suitable conditions for the study of dioxygen uptake.

Thermodynamic studies on the addition of molecular oxygen to Co(II)-1,4,8,12 tetraazacyclopentadecane in aqueous solution at 25C

Aqueous solutions containing Co2+ and the macrocyclic ligand 1,4,8,12-tetraazacyclopentadecane (L) are able to bind reversibly molecular oxygen to form the species Co2L2O24+ between pH 5 and 7. This species at pH greater than 8 is replaced by the complex Co2L2O2 (OH)22+ whose concentration in the solution increases to about pH 10.5. At pH greater than 10.5, Co(II) exists totally in this μ-peroxobisydroxo complex. Both the above mentioned oxygenated forms suffer a relatively slow irreversible oxidation to Co(III). From oxygen binding curves, approximate values of the equilibrium constants were calculated for the addition of oxygen to CoL2+ to form the μ-peroxo and the μ-peroxo-bishydroxo complexes. The enthalpies of formation of this latter complex starting from both Co2+ or CoL2+ have been obtained by means of calorimetric measurements. The effects of the size of the macrocyclic ligand on the affinity and the enthalpy of oxygen binding have been considered.

Thermodynamic studies on the addition of molecular oxygen to cobalt(II) complexes. Part 1. The cobalt(II)–ethylenediamine–oxygen system in aqueous solution at 25 °C

The equilibrium constant for the formation of [Co2(en)4(O2)(OH)]3+(en = ethylenediamine) in 1 mol dm–3 KCI aqueous solution, at 25 °C, has been determined using polarographic oxygen analysis, pH metric, and spectrophotometric techniques. The enthalpy of formation of this complex has been obtained by direct calorimetric measurements. The thermodynamic functions for the addition of O2 to [Co(en)2]2+ in order to form the doubly bridged dicobalt complex [Co2(en)4(O2)(OH)]3+ have been calculated. The enthalpy change is very large, but the stability of the binuclear species with respect to [Co(en)2]2+ is strongly reduced by a large entropy effect which cannot be explained in terms of the value of the partial molar entropy of oxygen in 1 mol dm–3 KCI solution.

Dioxygen addition to cobalt(II) complexes with a binucleating macrocyclic ligand

The behavior of Co(NO3)2 and 1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane aqueous solutions towards molecular dioxygen has been examined over a large range of ratios R between the ligand and cobalt(II) concentrations and in the presence of different types of anions at high concentrations. Both binuclear, Co2L(O2)(OH), and mononuclear, Co(HmL)(O2), peroxo complexes are formed depending on the value of R. The formation of the binuclear species is rapid, while that of the mononuclear complexes is slow. Phosphate anions (Y) enter into the bi- and mono-nuclear peroxo complexes, giving Co2L(O2)Y and CoL(O2)Y species. The kinetics of dioxygen uptake under various experimental conditions has been studied and reaction schemes are proposed.