Giuliana Tomat

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.

The crystal structure of tetraethylenglycoltrinitrato lanthanum(III): an example of undecacoordination

Abstract The title compound has been prepared by reacting La(NO 3 ) 3 with tetraethylenglycol. The structure was determined from counter-collected data and refined to R = 0.049 for 2310 reflections. The space group is P2 1 /n, monoclinic, with cell dimensions a = 12.75(1), b = 16.84(1), c = 8.15(1) A, β = 101.27(3)°, D x = 2.01 g cm −3 for Z = 4. The pentadentate organic ligand wraps around the metal ion which is also bound to three chelate nitrato groups, thus achieving the rather uncommon undeca-coordination. Five La-O(nitrate) (mean 2.61 A) compare well with the two LaO(alcohol) bond distances (mean 2.58 A). One LaO (nitrate) (2.79 A) and the three LaO(ether) bond distances (mean 2.70 A) are significantly longer. Weak intra- and intermolecular hydrogen bonds are also present.

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.

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.

Lanthanide complexes of 5-nitrophenol and its 1,3-Xylyl crown derivatives, 15-crown-4 and 18-crown-5, in aqueous solution

Abstract The stabilities of the one-one complexes of some lanthanide ions with p -nitrophenolate and its 1,3-xylyl crown derivatives, 15-crown-4 (I) and 18-crown-5 (II) , have been determined in aqueous solution at 25 °C by potentiometric measurements of the hydrogen ion concentration. Both the two cyclic ligands form complexes which are stronger than those of the p -nitrophenol, indicating that the ethereal chains are involved in the complex formation. A consideration of the stability constants as a function of the atomic number of the lanthanides obtained for the two cyclic ligands I and II suggests that in these coordination systems the phenoxide oxygen atom is the primary binding site while the ethereal oxygen atoms act as secondary binding sites with the metal ion probably located outside the cavity of the macroring.

Thermodynamics of lanthanide(III) complex formation with nitrogen-donor ligands in dimethyl sulfoxide

Potentiometric and calorimetric data for the complexation of lanthanide(III) cations by the neutral nitrogen-donor ligands diethylenetriamine or triethylenetetramine in anhydrous dimethyl sulfoxide at 25 °C and in an ionic medium of 0.1 mol dm–3 NEt4ClO4 have been obtained. All the complexes are strongly enthalpy stabilized while the entropy changes are unfavourable. The results are discussed in terms of the charge density of the metal ions, the solvation changes along the lanthanide(III) series and the structural and conformational characteristics of the ligands.

Thermodynamics of vanadyl(IV)—carboxylate complex formation in aqueous solution

Abstract The stability constants and the heats of formation of vanadyl(IV)—acetate, —glycolate, and —glycine complexes have been determined in aqueous solution by means of potentiometric and calorimetric measurements. In the pH range where the protolitic equilibria of VO 2+ is certainly negligible the acetate forms two mononuclear complexes, the glycolate three whereas the glycine reacts in its zwitterionic form. The stabilities of the glycolate complexes are considerably higher than the acetate ones, in spite of its lower basicity, indicating that the complex formation involves the coordination of the hydroxyl group to the metal ion. The enthalpy changes are positive except for the glycolate where a small negative value is found. For all systems the entropy changes are positive and therefore favourable to the complex formation.

Oxydiacetato complexes of thorium (IV), the crystal structures of tetra-aquo bis (oxydiacetato) thorium (IV) hexahydrate and di (sodium nitrate) disodium tris (oxydiacetato) thorium (IV)

Abstract The crystal and molecular structures of Th(oda)2(H2O)4·6H2O (1) and Na2[Th(oda)3]·2NaNO3 (2) (oda = oxydiacetate) have been determined from three-dimensional X-ray diffraction data and refined by least squares to R = 0.049 and Rw = 0.049 for 2265 independent reflections for (1) and to R = 0.024 and Rw = 0.023 for 2196 independent reflections for (2). Crystal parameters are as follows: (1), tetragonal, space group P41212, a = 10.335(2), c = 20.709(5) A and Z = 4; (2), monoclinic, space group C2/c, a = 17.096(5), b = 9.451(2), c = 16.245(4) A, β = 107.8(1) and Z = 4. In both compounds the thorium atom lies on a crystallographic two-fold axis. The co-ordination number for thorium in (1) is 10 (bicapped square antiprism geometry), the compound is monomeric, the two oda ligands are tridentate to the metal, and four water molecules complete the coordination sphere; in thorium (2) the coordination number is 9 (tricapped trigonal prism geometry) with three oda ligands tridentate to the metal, the [Th(oda)3]2− and NO3− anions are held together through the sodium ions which are coordinated both to the oda carboxylic oxygens and to the nitrate oxygens. The ThO coordination distances are: in (1) 2.411(8), 2.414(9) for the carboxylic oxygens, 2.479(10) and 2.486(8) for water molecules and 2.697(9) for the etheric oxygen and in (2) 2.384(3), 2.402(4) and 2.402(4) for the carboxylic oxygens, 2.559(5) and 2.562(4) A for the etheric oxygens.

Equilibrium measurements for silver(I) complexes with polyamines in dimethyl sulphoxide

The stability constants of silver(I) complexes with 1,2-diaminoethane (en), 1,3-diaminopropane (tn), and diethylenetriamine (dien) in dimethyl sulphoxide (dmso) at 25 °C and at an ionic strength of 0.1 mol dm–3 have been determined by potentiometry. Within the silver and ligand concentration ranges investigated, two mononuclear complexes have been found for the Ag+–en and –dien systems; with tn, polynuclear complexes are formed in addition to a mononuclear species. The ligands all behave as chelating agents, en forming a five-membered chelate ring and tn a six-membered one; dien co-ordinates as a terdentate ligand. All the complexes are stronger in dmso than in water. The effects of the two solvents on the interaction between silver(I) and N-donor ligands are discussed.