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The synthesis of a novel family of heterobinuclear cofacial biphenylene (B), anthracene (A), 9,9-dimethylxanthene (X) or dibenzofuran (O) bridged porphyrin-corrole complexes, (PCY)MCICoCl, is reported, M being either an iron(III) or manganese(III) ion. Each complex is characterized by electrochemistry, mass spectrometry, UV-vis, IR, and electron spin resonance spectroscopy.

The first reproducible synthetic route to a UO(sub 2)(super +) coordination complex via a two-electron oxidation of U(III) and the first structurally characterized dioxouranium(V) halide that is found to form a one-dimensional (1D) coordination polymer in the presence of potassium iodide is described. The characteristic visible-NIR bands and the infrared UO(sub 2) asymmetric stretching frequency of the resultant green pyridine solution of the salophen complex have agreed with the presence of a pentavalent uranyl species confirming the versatility of the compound as a reagent for the preparation of new uranyl(V) complexes.

Three face-to-face linked porphyrin-corrole dyads are investigated as to their electrochemistry, spectroelectrochemistry, and chloride-binding properties in dichloromethane or benzonitrile. An axial binding of one or two Cl(super -) ligands to the cobalt center of the corrole is observed for singly and doubly oxidized (PCY)H2Co, with the exact stoichiometry of the reaction depending upon the spacer size and the concentration of Cl(super -) added to solution.

Three series of cobalt(III) corroles were tested as catalysts for the electroreduction of dioxygen to water. Cyclic voltammetry and rotating ring-disk electrode voltammetry were both used to examine the catalytic activity of the cobalt complexes in acid media.

The reaction of {[U[O.sub.2][Py.sub.5][[K].sub.2-][Py.suib.2]}.sub.n] polymer is investigated. The findings expand the scope for the preparation of polymetallic assemblies involving f-elements and a rich chemistry can be anticipated from the reaction of pentavalent uranyl with different metal cations.

We describe here the full synthesis of a novel family of bifunctional ligands and present a complete study of their extraction properties in regards to an aqueous phosphoric acid solution containing uranium. We developed a high yielding synthesis of amido phosphonate ligands and focused our investigation on the effect of steric hindrance on the methylene bridge between the two functions. These new bifunctional ligands were found to extract selectively hexavalent uranium U(VI) with high distribution coefficient (D) and selectivity towards iron Fe (III) in 5 M phosphoric acid solution. From a structure-activity approach a specific ligand called DEHCNPB has been put forward in regard to the outstanding results obtained for the selective extraction, and quantitative recovery of uranium compared to the URPHOS reference system. [ABSTRACT FROM PUBLISHER]

Ligand systems containing amido-phosphonic acid moieties were synthesized for subsequent U(VI) extraction from phosphoric acid solutions. Studies have shown that the efficiency of extraction (distribution ratios and selectivity of U(VI) over Fe(III)) is influenced by the nature of the N-dialkyl substituents and the length and nature of the spacer. A structure-activity approach resulted in the identification of a specific ligand called DEHCBPA that exhibited larger D-values than the corresponding URPHOS reference system. The distribution ratios for U(VI) extraction increased considerably with a branched N-dialkyl chain when a steric hindrance was introduced into the methylene bridge of the amido-phosphonic acid ligands. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the development of a model which calculates the composition of the organic phase for a system used to remove selectively americium from a PUREX raffinate. A phenomenological approach is performed to aggregate step by step the specificities of this complex extraction system. Modeling of the influence of TEDGA is complex because experiments have shown that the water-soluble ligand TEDGA is extracted by the diamide and that its extraction is enhanced in presence of lanthanides. The formation of mixed solvates lanthanides-TEDGA-DMDOHEMA is thus taken into account. [Copyright &y& Elsevier]

Abstract: Selected soft N-donor ligands are highly effective extractants for the separation of trivalent actinides (An(III)) from lanthanides (Ln(III)) in the partitioning and transmutation (P&T) strategy. Comparative structural investigations using X-ray absorption spectroscopy (EXAFS) on An(III) and Ln(III) complexed with tris[(2-pyrazinyl)methyl]amine (TPZA) and 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (BTP) are performed in order to evaluate if ligand extraction performance is reflected in coordination structure differences, specifically in variations in the metal cation–N bond lengths. We observe U(III) to generally exhibit a decrease in the bond distance over that expected for pure ionic binding for the ligand complexes investigated and interpret this as higher covalent character of the U(III)–N binding. In contrast, no measurable differences for Am(III), Cm(III), and the Ln(III) elements in the middle of the 4f series are observed. Time-resolved laser fluorescence spectroscopy (TRLFS) investigations on solution BTP complexed with Cm(III) and Eu(III) reveal that the selective extraction behavior of this ligand can be explained by the large difference in conditional stability constants of their 1:3 complexes (K 13). The K 13 value for Cm–BTP3 is a number of orders of magnitude larger than that for Eu–BTP3. [Copyright &y& Elsevier]

Combined electrochemical and UV-visible spectroelectrochemical methods were utilized to elucidate the prevailing mechanisms for electroreduction of previously synthesized porphyrin-corrole dyads of the form (PCY)H2Co and (PCY)MClCoCl where M = Fe(III) or Mn(III), PC = porphyrin-corrole, and Y is a bridging group, either biphenylenyl (B), 9,9-dimethylxanthenyl (X), anthracenyl (A), or dibenzofuranyl (O). These studies were carried out in pyridine, conditions under which the cobalt(IV) corrole in (PCY)MClCoCl is immediately reduced to its Co(III) form, thus enabling direct comparisons with the free-base porphyrin dyad, (PCY)H2Co(III) under the same solution conditions. The compounds are all reduced in multiple one-electron-transfer steps, the first of which involves the M(III)/M(II) process of the porphyrin in the case of (PCY)MClCoCl and the Co(III)/Co(II) process of the corrole in the case of (PCY)H2Co. Each metal-centered redox reaction may be accompanied by the gain or loss of pyridine axial ligands, with the exact stoichiometry of the exchange process depending upon the specific combination of metal ions in the dyad, their oxidation states, and the particular spacer in the complex. Before this study was started, it was expected that the porphyrin-corrole dyads with the largest spacers, namely, O and A, would readily accommodate the formation of cobalt(III) bis-pyridine adducts because of the larger size of the cavity while dyads with the smallest B spacer would seem to have insufficient room to add even a single pyridine within the cavity, as was structurally seen in the case of (PCB)H2Co(py). This is clearly not the case, as shown in the present study. A reversible Co(III)/Co(II) reaction is seen for (PCB)MnClCoCl at -0.62 V, which when combined with spectroscopic data, leads to the assignment of (PCB)Mn(III)(py)2Co(III)(py) as the species in pyridine. The reduction of (PCB)Mn(III)(py)2Co(III)(py) to (PCB)Mn(II)(py)Co(III)(py) is accompanied on the slower spectroelectrochemical time scale by the appearance of a 603 nm band in the UV-vis spectra and is consistent with the addition of a second pyridine ligand to the Co(III)(py) unit of the dyad as one ligand is lost from the electrogenerated manganese(II) porphyrin, thus maintaining one pyridine ligand within the cavity. A different change in the coordination number is observed in the case of (PCB)FeClCoCl. Here the initial Fe(III) complex can be assigned as (PCB)Fe(III)ClCo(III)(py), which has no pyridine molecule within the cavity and the singly reduced form is characterized as (PCB)Fe(II)(py)2Co(III)(py)2, which contains two pyridine ligands inside the cavity. A following one-electron reduction of the Fe(II)/Co(III) complex then gives [(PCB)Fe(II)(py)2Co(II)]-.