Roberto Portanova

Critical evaluation of stability constants for alpha-hydroxycarboxylic acid complexes with protons and metal ions and the accompanying enthalpy changes. Part II. Aliphatic 2-hydroxycarboxylic acids (IUPAC Technical Report)

Stability constants for different aliphatic 2-hydroxycarboxylic acid complexes in aqueous solutions with protons and metal ions published between 1960 and the end of 1994 have been critically evaluated.

Relative stabilities of complexes of MO22+ (M = U, Np, and Pu) with monocarboxylate anions

Abstract Stability data for complexes of yl(VI) ions MO 2 2+ (M = U, Np, and Pu) with monocarboxylic ligands L are reported and discussed (L = CH 3 CO 2 − , C 2 H 5 CO 2 − , and CH 2 ClCH 2 CO 2 − ). Stability constants refer to the formation equilibria of complexes in aqueous NaClO 4 solution at 20° and 1 M ionic strenght. In the range of ligand concentrations examined, complexes are formed in which the highest average ligand number, n is three. The stability order of complexes of the various ligands examined is UO 2 2+ >NpO 2 2+ >PuO 2 2+ . The stabilities of complexes of a given MO 2 2+ ion increase with increasing ligand basicity, which suggests a strong hard character for these oxycations.

Lanthanide(III) complex formation with diethylenetriamine in anhydrous N,N-dimethylformamide

Abstract The formation of diethylenetriamine (dien) complexes of the lanthanide(III) ions has been studied in N,N-dimethylformamide (dmf) containing 0.1 mol dm−3 tetraethylammoniumtrifluoromethanesulfonate as constant ionic medium at 298 K. The stability constants have been obtained by potentiometry using the method of competitive reactions, silver(I) being the auxiliary central ion. The thermodynamic investigations have therefore been extended also to this metal ion. The data concerning lanthanide(III) complexation are well explained in terms of formation of two successive mononuclear complexes which are enthalpy stabilized, entropy changes being unfavourable. Dien coordinates with all N atoms both in ML and ML2 lanthanide(III) complexes; with silver(I), tridentation is achieved only when the first mononuclear complex is formed. The trends in enthalpy and entropy values of the lanthanide(III) complexes are discussed taking into account the presence of multiple solvation equilibria which involve the bare ions and the complexes in solution. Comparison with similar data previously obtained in dimethylsulfoxide (dmso) both for the lanthanide(III)- and silver(I)-dien systems, shows the remarkable influence of the solvent on the thermodynamics of complex formation.

Oxygenation reaction of Co(trien)2+ complex in dimethylsulfoxide and the aerobic oxidation of 2,6-di-tert-butylphenol catalyzed by Co(II)–amine complexes

Abstract The kinetics and the thermodynamics of the oxygenation reaction of Co(trien)2+ complex (trien=1,4,7,10-tetraazadecane) have been studied in dimethylsulfoxide (dmso) at 298 K and in a medium adjusted to 0.1 mol dm−3 with Et4NClO4 by means of UV–Vis spectrophotometric technique. The reaction mechanism is consistent with the fast formation of an initial CoL–O2 species, followed by a rate determining step which gives the final (CoL)2O2 adduct. The results are compared with similar data in water and discussed considering the effects of ligand/solvent substitution. The catalytic activity of Co(trien)2+ as well as that of other diamine complexes, CoL2 (L=ethylenediamine (en), N,N′-dimethylethylenediamine) has also been tested towards the aerobic oxidation of 2,6-di-tert-butylphenol in mild conditions and the results are discussed in term of both catalytic ability and selectivity.

Thermodynamics of complex formation in dimethyl sulphoxide. Silver(I) with quadridentate polyamines

The changes in free energy, enthalpy, and entropy for the complex-formation reactions in dimethyl sulphoxide (DMSO) between silver(I) and tetraamines 1,4,7,10-tetraazadecane (TRIEN), tris(2-aminoethyl)amine (TREN), and 1,5,8,12-tetraazadodecane (TNENTN) have been determined by potentiometric and calorimetric measurements at 25 °C and an ionic strength of 0.1 mol dm–3. All three amines form the very stable 1 : 1 complexes, acting as tetradentate ligands. Only TREN and TNENTN form other mono- and poly-nuclear coordinated species. Compositions and stabilities of the complexes are discussed in relation to the different structures of the ligands. From a comparison of the available experimental results on silver (I)–amino complexes in the two solvents, water and DMSO, some conclusions are made regarding the main factors determining the coordination properties in these systems.

Complex of plutonyl ion with acetate

Abstract The complex formation between plutonyl and acetate ion has been investigated by means of potentiometric [H + ] measurements. The value of the complexity constants of the three mononuclear complexes have been determined in perchlorate medium of ionic strength I = 1 M at 20°C.

Affinity of lanthanide(III) ions for oxygen- and mixed oxygen-nitrogen-donor ligands in dimethylsulfoxide: a thermodynamic and spectroscopic investigation

Abstract The interactions of lanthanide(III) ions with the following oxygen- and mixed oxygen–nitrogen-donor ligands: 2-methoxyethylamine ( L1 ), 2-aminoethanol ( L2 ), 2-methoxyethylether ( L3 ), di(ethyleneglycol) ( L4 ), 2,2′-oxydiethylamine ( L5 ) and 1,5-diaminopentane ( L6 ) have been investigated in dimethylsulfoxide (DMSO) at 298 K and I =0.1 mol dm −3 (Et 4 NClO 4 ). Calorimetric and 1 H NMR results show that L1 – L4 and L6 are not able to complex Ln(III) ions. L5 is shown to be able to bind heavier Ln(III) ions (LnHoLu). Potentiometric and calorimetric measurements have been carried out to obtain the Ln(III)– L5 thermodynamic parameters of complexation. All the complexes are formed in exothermic reactions being the entropy terms generally negative or slightly positive. Comparison between the complexing abilities of L1 and L5 shows that at least two CH 2 CH 2 NH 2 side-arms added to an ether function are needed to promote effective interaction between an ether O atom and Ln(III) ions in the high coordinating solvent DMSO. The results are discussed in terms of different donor properties and solvation of NR and O groups towards metal ions. A comparison with data previously obtained in DMSO for the complex formation of Ln(III) with the purely N donor diethylenetriamine (dien) is made.

Silver(I)–polyamine systems in dimethyl sulphoxide. A thermodynamic and spectroscopic investigation

The thermodynamic parameters ΔG°, ΔH° and ΔS° of complexes of silver(I) with 3,3′-diaminopropylamine(DPT) as well as the heats of formation of silver(I) with 1,2-diaminoethane (EN), 1,3-diaminopropane (TN), and diethylenetriamine (DIEN) have been measured in dimethyl sulphoxide (DMSO) at 25 °C and in a medium of ionic strength 0.1 mol dm–3. N.m.r. spectra of solutions of silver(I) and ligands investigated have also been performed. From a combination of thermodynamic and spectroscopic data conclusions are drawn about the nature and structure of the complexes formed in solution. The silver(I) complexes are all stronger in DMSO than in water, reflecting the higher solvation of the ligands in water, through stronger hydrogen bonds, than in DMSO.

Equilibrium and enthalpy measurements on the copper(I) and silver(I) chloride, bromide, iodide and thiocyanate systems in tetrahydrothiophene

Abstract Potentiometric and calorimetric measurements have been carried out for the determination of the stability constants and the enthalpy changes of the formation of copper(I) and silver(I) halide and thiocyanate complexes in tetrahydrothiophene (THT). THT is a sulfur donor solvent, which solvates the soft acceptors copper(I) and silver(I) well. THT has a low dielectric constant ϵ≈8, which affects the stability constants and the complex distribution, since the solvent has limited ability to neutralize ionic charges. Two mononuclear complexes are formed in all systems. The stabilities of the stepwise silver(I) halide complexes increase in the order Cl − − − . The stabilities of the first copper(I) halide complexes are almost identical, while the stabilities of the second copper(I) halide complexes follow the sequence Cl − >Br − − . The neutral complexes of these systems are considerably more stable in THT than in any other previously studied solvent, in spite of the strong solvating properties of THT. This is because the electrostatic forces become predominant in a solvent with a low dielectric constant where charges are neutralized through ion pair formation. The enthalpy changes of the formation of the first complexes are small and negative, except for copper- (I) chloride and iodide where small positive values are found. For all systems, the second complexes are formed in strongly endothermic reactions.

Co(II) and Cd(II) complexation with two dipyridine-containing macrocyclic polyamines in water and dimethyl sulfoxide

Solvent effects in the formation of Co(II) and Cd(II) complexes with the two macrocyclic ligands 2,5,8,11,14-pentaaza[15]-[15](2,2′)[1,15]-bipyridylophane (L1) and trimethyl-5,8,11-2,5,8,11,14-pentaaza[15]-[15](2,2′)[1,15]-bipyridylophane (L2), both containing dipyridine units, were analysed by determining the thermodynamic parameters (logK, ΔH°, TΔS°) for the complexation reactions in water and dimethyl sulfoxide (DMSO) by means of potentiometric, spectrophotometric and calorimetric techniques. N-Methylation leads to different solvation properties of the ligands and to different abilities in stabilizing metal complexes via the formation of M–NH⋯S hydrogen bonds to solvent molecules (S) which enhances the σ-donating properties of the donor atom. In contrast to expectations based on the stronger solvation of Cd(II) and Co(II) in DMSO than in water, complexes with L1 display higher stability in DMSO than in water, indicating that ligand solvation, instead of metal ion solvation, plays a major role in determining the stability of L1 complexes in the two solvents. On the other hand, for ligand L2, in which tertiary amino groups are present, an almost opposite trend of stability is observed. Because L2 is less solvated than L1 in water and tertiary nitrogens are weaker bases in DMSO than in water, the stronger solvation of metal ions in DMSO prevails in determining the stability of L2 complexes. Semi-empirical calculations were also performed to obtain some structural information in the gas phase.