Marilena Tolazzi

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.

Thermodynamic and Spectroscopic Studies of Lanthanides(III) Complexation with Polyamines in Dimethyl Sulfoxide

The thermodynamic parameters of complexation of Ln(III) cations with tris(2-aminoethyl)amine (tren) and tetraethylenepentamine (tetren) were determined in dimethyl sulfoxide (DMSO) by potentiometry and calorimetry. The excitation and emission spectra and luminescence decay constants of Eu3+ and Tb3+ complexed by tren and tetren, as well as those of the same lanthanides(III) complexed with diethylenetriamine (dien) and triethylenetetramine (trien), were also obtained in the same solvent. The combination of thermodynamic and spectroscopic data showed that, in the 1:1 complexes, all nitrogens of the ligands are bound to the lanthanides except in the case of tren, in which the pendant N is bound. For the larger ligands (trien, tren, tetren) in the higher complexes (ML2), there was less complete binding by available donors, presumably due to steric crowding. FT-IR studies were carried out in an acetonitrile/DMSO mixture, suitably chosen to follow the changes in the primary solvation sphere of lanthanide(III) due to complexation of amine groups. Results show that the mean number of molecules of DMSO removed from the inner coordination sphere of lanthanides(III) is lower than ligand denticity and that the coordination number of the metal ions increases with amine complexation from approximately 8 to approximately 10. Independently of the number and structure of the amines, linear trends, similar for all lanthanides, were obtained by plotting the values of DeltaGj degrees, DeltaHj degrees, and TDeltaSj degrees for the complexation of ethylenediamine (en), dien, trien, tren, and tetren as a function of the number of amine metal-coordinated nitrogen atoms. The main factors on which the thermodynamic functions of lanthanide(III) complexation reactions in DMSO depend are discussed.

Energetics and structure of uranium(VI)-acetate complexes in dimethyl sulfoxide.

The thermodynamics of the complexation between uranium(VI) and acetate in dimethyl sulfoxide (DMSO) was studied at 298 K in an ionic medium of 0.1 mol dm(-3) tetrabutyl ammonium perchlorate. The results show that the uranyl ion forms three strong successive mononuclear complexes with acetate. The complexes, both enthalpically and entropically stabilized, are significantly more stable in DMSO than in water. This feature can be ascribed to the weak solvation of acetate in DMSO. The thermodynamic parameters for the formation of the uranium(VI) complexes with acetate in DMSO are compared with those with ethylenediamine in the same solvent. The difference between the two ligand systems reveals that, for the complexation reactions involving charge neutralization, the reorganization of the solvent gives a very important contribution to the overall complexation energetics. The coordination mode of acetate in the uranyl complexes and the changes of the solvation sphere of UO(2)(2+) upon complexation were investigated by FT-IR spectroscopy in DMSO and in acetonitrile/DMSO mixtures. In addition, DFT calculations were performed to provide an accurate description of the complexation at the molecular level. The experimental and calculated results suggest that acetate is solely bidentate to UO(2)(2+) in the 1:1 and 1:3 complexes but mono- and bidentate in the 1:2 complexes. The DFT calculations also indicate that the medium effects must always be taken into account in order to gain accurate information on the complex formation in solution. In fact, the relative stability of the reaction products changes markedly when the DFT calculations are carried out in vacuum or in DMSO solution.

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.

Nickel(II) Complexation with Nitrate in Dry [C4mim][Tf2N] Ionic Liquid: A Spectroscopic, Microcalorimetric, and Molecular Dynamics Study

The complex formation of nitrate ions with nickel(II) in dry [C4mim][Tf2N] ionic liquid (IL) was investigated by means of UV-visible spectrophotometry, isothermal titration calorimetry (ITC), extended X-ray absorption fine structure spectroscopy (EXAFS), and molecular dynamics (MD) simulations. EXAFS spectroscopy and MD simulations show that the solvated Ni(II) cation is initially coordinated by the oxygens of the [Tf2N](-) anion of IL, which can behave either as mono- or bidentate. Spectroscopic and thermodynamic data show that Ni(II) is able to form up to three stable mononuclear complexes with nitrate in this solvent. The stability constants for Ni(NO3)j complexes (j = 1-3) calculated from spectrophotometry and ITC experiments decrease in the order log K1 > log K2 > log K3. The formation of the first two species is enthalpy-driven, while the third species is entropy-stabilized. The UV-vis spectra of solutions containing different nitrate/Ni(II) ratios show that the metal ion retains the six-coordinate geometry. Furthermore, the EXAFS evidences that nitrate is always bidentate. Molecular dynamics simulations show that the [Tf2N](-) anions bind Ni(II) through the sulfonyl oxygen atoms and can coordinate either as monodentate or chelate. The analysis of the MD data shows that introduction of nitrates in the first coordination sphere of the metal ion results in remarkable structural rearrangement of the ionic liquid.

Thermodynamics of the Complexation of Uranium(VI) by oxalate in aqueous solution at 10-70oC

The protonation reactions of oxalate (ox) and the complex formation of uranium(vi) with oxalate in 1.05 mol kg(-1) NaClO(4) were studied at variable temperatures (10-70 degrees C). Three U(vi)/ox complexes (UO(2)ox(j)((2-2j)+) with j = 1, 2, 3) were identified in this temperature range. The formation constants and the molar enthalpies of complexation were determined by spectrophotometry and calorimetry. The complexation of uranium(vi) with oxalate ion is exothermic at lower temperatures (10-40 degrees C) and becomes endothermic at higher temperatures (55-70 degrees C). In spite of this, the free energy of complexation becomes more negative at higher temperatures due to increasingly more positive entropy of complexation that exceeds the increase of the enthalpy of complexation. The thermodynamic parameters at different temperatures, in conjunction with the literature data for other dicarboxylic acids, provide insight into the relative strength of U(vi) complexes with a series of dicarboxylic acids (oxalic, malonic and oxydiacetic) and rationalization for the highest stability of U(vi)/oxalate complexes in the series. The data reported in this study are of importance in predicting the migration of uranium(vi) in geological environments in the case of failure of the engineering barriers, which protect waste repositories.

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.

Thermodynamics of the complex formation between silver(I) and mixed phosphorus-sulfur ligands in dimethyl sulfoxide

Abstract The thermodynamics of complex formation between silver(I) and the ligands Ph2PCH2SR (RMe, Ph) and Ph2P(CH2)2SR (REt, Me, Ph) has been determined in dimethyl sulfoxide (dmso) at 25 °C and in a medium of ionic strength 0.1 mol dm−3 by potentiometric and calorimetric measurements. Within the silver and ligand concentration ranges investigated, three mononuclear complexes have been determined. All the complexes are strongly enthalpy stabilized while the entropy changes are unfavourable. The ligands all behave as monodentate, coordinating the silver ion through the phosphorus atom. The influence of the length of the aliphatic chain between the donor atoms as well as of the nature of R on the stabilities of the complexes formed are discussed.

Hydration of Two Cisplatin Aqua-Derivatives Studied by Quantum Mechanics and Molecular Dynamics Simulations

The hydration of the cisplatin aqua-derivatives, cis-[PtCl(H2O)(NH3)2](+) (w-cisplatin) and cis-[Pt(H2O)2(NH3)2](2+) (w2-cisplatin), has been studied by means of classical molecular dynamics simulations. The new platinum complex-water interaction potential, w-cisplatin-W, has been built on the basis of the already obtained cisplatin-water interaction potential (cisplatin-W) [J. Chem. Theory Comput. 2013 9, 4562]. That potential has been then transferred to the w2-cisplatin-W potential. The w-cisplatin and w2-cisplatin atomic charges were specifically derived from their solutes wave functions. Bulk solvent effects on the complex-water interactions have been included by means of a continuum model. Classical MD simulations with 1 platinum complex and 1000 SPC/E water molecules have been carried out. Angle-solved radial distribution functions and spatial distribution functions have been used to provide detailed pictures of the local hydration structure around the ligands (water, chloride, and ammine) and the axial region. A novel definition of a multisite cavity has been employed to compute the hydration number of complexes in order to provide a consistent definition of their first-hydration shell. Interestingly, the hydration number decreases with the increase of the complex net charge from 27 for cisplatin to 23 and 18 for w-cisplatin and w2-cisplatin, respectively. In parallel to this hydration number behavior, the compactness of the hydration shell increases when going from the neutral complex, i.e. cisplatin, to the doubly charged complex, w2-cisplatin. Quantum mechanics estimation of the hydration energies for the platinum complexes allows the computation of the reaction energy for the first- and second-hydrolysis of cisplatin in water. The agreement with experimental data is satisfactory.