P. Di Bernardo

Thermodynamic properties of actinide complexes—II: Thorium(IV)-acetate system

The changes in free energy, enthalpy and entropy for the formation of thorium(IV)--acetate complexes have been determined at 25/sup 0/C and in 1.00 M aqueous perchlorate-medium. All five complexes formed, are found to be stabilized by a large gain of entropy. The marked increase in the values of ..delta..H/sub j/ and ..delta..S/sub j/, relative to the third step of complexation has been explained in terms of a coordination change.

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.

Thermodynamic properties of actinide complexes—IV Thorium(IV)- and uranyl(VI)-malonate systems

Abstract The stability constants and the enthalpies of formation of thorium(IV)- and uranyl(VI)-malonate complexes have been determined by potentiometric and calorimetric titrations in 1.00 M solutions of Na(ClO 4 ) at 25°C. All complexes formed are found to be stabilized by a large entropy gain. The values for the stability constants agree with an ionic bonding model. The malonate behaves as a bidentate ligand forming only chelate complexes.

Thermodynamic properties of actinide complexes. Part. III. Uranyl(VI)-glycolate system

Abstract The changes in free energy, enthalpy and entropy for the formation of uranyl(VI)-glycolate complexes, have been determined at 25 °C and in aqueous perchlorate medium 1.00 M. All three complexes formed, are found to be stabilized by entropy, while the enthalpy term, excepting the third step, opposes the complex formation. The data are in agreement with the presence of chelate structures in a decreasing measure for each of the three successive steps of complexation.

Polarographic Investigations on Uranyl(VI) Complexes in Dimethylsulfoxide. 1. Monocarboxylic Ligands.

Abstract The formation of acetate, glycolate, chloroacetate and β-chloropropionate complexes of uranium(VI) in dimethylsulfoxide has been investigated by the polarographic method. 0.1 M tetrabutylammonium perchlorate was used as supporting electrolyte. The 3:1 acetate and the 1:1 glycolate complexes give distinct cathodic waves; the polarographic behaviour allows to evidentiate also the 1:1 and 2:1 acetate, the 1:1 chloroacetate and β-chloropropionate complex formation. The formed complexes are stronger in DMSO than in water and the more so the harder the ligand. The (a)-character of uranyl ion is more marked in DMSO than in aqueous media.

Photochemistry of actinide complexes. III. The photoproduction mechanism of uranium(V) oxochloro-complexes

Abstract The photochemical preparation of oxochloro-complexes UOCl 3 , UOCl 5 (C 5 H 5 NH) 2 , and U(V) ethoxide, U(OC 2 H 5 ) 5 , is described. The absorption spectra of these U(V) complexes were measured and discussed. Irradiation of [UO 2 Cl 2 · (C 5 H 5 N) 2 ] complex in dry ethanol and in the presence of radical scavengers is considered to yield UO 2 Cl as primary photoproduct which gives rise by thermal or secondary photochemical reaction to UOCl 3 . Thermal reaction of UOCl 3 with pyridinium hydrochloride, formed in the photoreaction mixture, leads to UOCl 5 (C 5 H 5 NH) 2 formation. Subsequent photoreaction of UOCl 5 (C 5 H 5 NH) 2 produces U(OC 2 H 5 ) 5 . The photochemical pathway to U(V) complexes compatible with the experimental observations is proposed.

Thermodynamic properties of actinide complexes Part V. Uranyl(VI)-thioglycolate system; thorium(IV)-glycolate and -thioglycolate systems

Abstract The changes in free energy, enthalpy and entropy for the formation of uranyl (VI)-thioglycolate, thorium(IV)-glycolate and -thioglycolate complexes have been determined. The changes in free energy were calculated from the stability constants, obtained from a potentiometric determination of the concentration of free hydrogen ion, using a glass or quinhydrone electrode. The enthalpy values were measured calorimetrically. The measurements were performed at 25.0°C in an aqueous sodium perchlorate medium with the total sodium concentration equal to 1.00 M. A comparison of the magnitude of the enthalpy and entropy changes for the various systems gives additional support of the view that the thioglycolate acts as a monodentate ligand while the glycolate forms chelate rings.

Complexation behaviour and stability of Schiff bases in aqueous solution. The case of an acyclic diimino(amino) diphenol and its reduced triamine derivative

The copper(II), nickel(II), and zinc(II) complexes of the acyclic Schiff base H(2)L(A), obtained by [1 + 2] condensation of 1,2-ethanediamine,N-(2-aminoethyl)-N-methyl with 3-ethoxy-2-hydroxybenzaldehyde, and of H(2)L(B), the reduced derivative of H(2)L(A), were prepared and their properties studied by IR, NMR and SEM-EDS. In these complexes, the metal ion is always located in the coordination chamber of the ligand delimited by two phenol oxygens and nitrogen atoms (either aminic or iminic). The coordination behaviour of H(2)L(A) and H(2)L(B) towards H(+), Cu(2+), Ni(2+) and Zn(2+) in aqueous solution at 298 K and mu = 0.1 mol dm(-3) (Na)ClO(4) was also studied by potentiometric, NMR and UV-VIS measurements. In particular, potentiometric equilibrium studies indicate that H(2)L(A) is not stable enough to have a pH range in which it is the sole species in aqueous solution. In such a solution, the Schiff base forms over a limited pH range, between 6 and 10, with a maximum formation percentage at pH approximately 9. In addition, the involvement of imine nitrogens in the complexes markedly stabilises the azomethylene linkage, so that the metal complexes of H(2)L(A), particularly those of copper(II), are the species largely prevailing in solutions with pH >3.5. The stability constants of the complexes formed by metal ions with H(2)L(A) and H(2)L(B) follow the order Cu(2+) >> Ni(2+) > Zn(2+); distribution plots show that copper(II) gives complexes more stable with H(2)L(A), whereas Ni(2+) and Zn(2+) prefer the reduced ligand, H(2)L(B).

The thermodynamics of 1,4,7,10,13- pentaazatridecane complexes of silver(I) in dimethyl sulfoxide

Abstract The thermodynamic parameters Δ G °, Δ H ° and Δ S ° for the formation of silver(I) mononuclear (AgL + ) and polynuclear ([Ag 2 L] 2+ , [Ag 3 L 2 ] 3+ ) complexes with 1,4,7,10,13-pentaazatridecane (L=tetren) have been obtained in dimethyl sulfoxide (dmso) at 25°C and in an ionic medium of 0.1 mol dm −3 . The complexes are enthalpy stabilized while the entropy contributions oppose their formation. Tetren, differently from other linear polyamines which have only aminoethylenic subunits and less than five nitrogens, is able to form polynuclear species in dmso. Structures and stabilities of the complexes are discussed in relation to the characteristics of the ligand.

The new 500 kV preinjector at LNS in Catania

Abstract A new 500 kV preinjector to be used mainly for tandem and superconducting cyclotron operation will be installed in front of the established one. The goal of the project is to be able to produce, easily and fast, high intensity heavy ion beams with high mass resolution.