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The ternary neptunium(V) (Np(V)) hydroxides Na0.5[NpO2(OH)1.5]·0.5H2O (I)and Na[NpO2(OH)2] (II)were synthesized in aqueous NaOH solutions at T= 80 °C, and their crystal structures were determined to be monoclinic, P21, Z= 2, a= 5.9859(2), b= 10.1932(3), c= 12.1524(4) Å, β = 98.864(1)°, V= 732.63(4) Å3for (I)and orthorhombic, P212121, Z= 4, a= 5.856(7), b= 7.621(9), c= 8.174(9) Å, V= 364.8(7) Å3for (II). By combining the detailed structural information with results from systematic solubility investigations, a comprehensive chemical and thermodynamic model of the Np(V) behavior in NaCl–NaOH solutions was evaluated. The results reveal a great stability of the ternary Na–Np(V)–OH solid phases that significantly enhances the predominance field of the entire Np(V) redox state to high alkalinity.

Neptunium was the first actinide element to be artificially synthesized, yet, compared with its more famous neighbours uranium and plutonium, is less conspicuously studied. Most neptunium chemistry involves the neptunyl di(oxo)-motif, and transuranic compounds with one metal–ligand multiple bond are rare, being found only in extended-structure oxide, fluoride or oxyhalide materials. These combinations stabilize the required high oxidation states, which are otherwise challenging to realize for transuranic ions. Here we report the synthesis, isolation and characterization of a stable molecular neptunium(V)–mono(oxo) triamidoamine complex. We describe a strong Np≡O triple bond with dominant 5f-orbital contributions and σu> πuenergy ordering, akin to terminal uranium-nitrides and di(oxo)-actinyls, but not the uranium–mono(oxo) triple bonds or other actinide multiple bonds reported so far. This work demonstrates that molecular high-oxidation-state transuranic complexes with a single metal–ligand bond can be stabilized and studied in isolation.

We performed a systematic study of the complexes of trivalent lanthanide cations with the hydridotris(1-pyrazolyl)borato (Tp) ligand (LnTp3; Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu) using both high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) and resonant inelastic X-ray scattering (RIXS) at the lanthanide L3absorption edge. Here, we report the results obtained and we discuss them against calculations performed using density functional theory (DFT) and atomic multiplet theory. The spectral shape and the elemental trends observed in the experimental HERFD-XANES spectra are well reproduced by DFT calculations, while the pre-edge energy interval is better described by atomic multiplet theory. The RIXS data show a generally rather complex pattern that originates from the intra-atomic electron–electron interactions in the intermediate and final states, as demonstrated by the good agreement obtained with calculations using an atomic-only model of the absorber. Guided by theoretical predictions, we discuss the possible origins of the observed spectral features and the trends in energy splitting across the series. The insight into the electronic structure of trivalent lanthanide compounds demonstrated here and obtained with advanced X-ray spectroscopies coupled with theoretical calculations can be applied to any lanthanide-bearing compound and be of great interest for all research fields involving lanthanides.

In view of safe management of the nuclear wastes, a sound knowledge of the atomic-scale properties of U1–xMxO2+ynanoparticles is essential. In particular, their cation valences and oxygen stoichiometries are of great interest as these properties drive their diffusion and migration behaviors into the environment. Here, we present an in-depth study of U1–xCexO2+y, over the full compositional domain, by combining X-ray diffraction and high-energy resolution fluorescence detection X-ray absorption near-edge structure. We show, on one hand, the coexistence of UIV, UV, and UVIand, on the other hand, that the fluorite structure is maintained despite this charge distribution.

A systematic investigation is presented which examines the structural chemistry of anhydrous and hydrous ternary hexavalent uranium and neptunium dinitrato, trinitrato, and tetranitrato complexes. Using slow evaporation methods under acidic conditions the uranium and neptunium nitrate complexes γ-K[UO2(NO3)3], K2[UO2-cis-(NO3)4], [NpO2(NO3)2(H2O)2]·4H2O, and Cs[NpO2(NO3)3] have been synthesized and their structures refined using single-crystal X-ray diffraction data. γ-K[UO2(NO3)3] adopts an orthorhombic structure in space group Pbcaconsisting of antiparallel aligned [UO2(NO3)3]−moieties. K2[UO2-cis-(NO3)4] adopts a monoclinic structure in space group P21/cconsisting of [UO2(NO3)4]2–moieties with two monodentate and two bidentate nitrate ligands that are arranged in a cisconfiguration about the uranyl, UO22+, center. Previous investigations have only identified transvariants of this monoclinic structure, and this is the first report of the cisform and also the occurrence of geometric isomerism in uranyl nitrates. [NpO2(NO3)2(H2O)2]·4H2O adopts an orthorhombic structure in space group Cmc21consisting of parallel aligned [NpO2(NO3)2(H2O)2] moieties that are in a transconfiguration with respect to the bidentate nitrate ligands. Cs[NpO2(NO3)3] adopts a hexagonal structure in space group R3cconsisting of parallel aligned [NpO2(NO3)3]−moieties. It was found that despite using a Np(V) nitrate solution as the starting reagent, Np(VI) nitrate structures were consistently recovered under acidic conditions. These observations are discussed and rationalized with respect to standard reduction potentials, particularly how redox conditions and acidity affect the oxidation state of Np and subsequent structure formation. The structures uncovered in this investigation are discussed comparatively and systematically in detail with other reported anhydrous and hydrous ternary hexavalent uranium and neptunium dinitrato, trinitrato, and tetranitrato complexes, particularly with respect to how synthesis conditions, including pH and geometric isomerism, affect the structural chemistry.

Intrinsic properties of a compound (e.g., electronic structure, crystallographic structure, optical and magnetic properties) define notably its chemical and physical behavior. In the case of nanomaterials, these fundamental properties depend on the occurrence of quantum mechanical size effects and on the considerable increase of the surface to bulk ratio. Here, we explore the size dependence of both crystal and electronic properties of CeO2nanoparticles (NPs) with different sizes by state-of-the art spectroscopic techniques. X-ray diffraction, X-ray photoelectron spectroscopy, and high-energy resolution fluorescence-detection hard X-ray absorption near-edge structure (HERFD-XANES) spectroscopy demonstrate that the as-synthesized NPs crystallize in the fluorite structure and they are predominantly composed of CeIVions. The strong dependence of the lattice parameter with the NPs size was attributed to the presence of adsorbed species at the NPs surface thanks to Fourier transform infrared spectroscopy and thermogravimetric analysis measurements. In addition, the size dependence of the t2gstates in the Ce LIIIXANES spectra was experimentally observed by HERFD-XANES and confirmed by theoretical calculations.

A study of neptunium (Np) chemistry in the complex oxo-selenium system has been performed. Hereby, two sets of precipitation experiments were conducted, investigating the influence of the initial oxidation state of selenium using SeIVO2and H2SeVIO4with NpVin alkali nitrate solution, keeping the ratio of Np/Se constant. Surprising results were observed. Five novel neptunium and selenium bearing compounds have been obtained by slow evaporation from aqueous solution. The novel NpIVphase K4-x[Np(SeO3)4-x(HSeO3)x]·(H2O)1.5(1) crystallizes in green-colored, plate-shaped crystals and was obtained by adding SeO2and ANO3to a NpVstock solution. Single-crystal X-ray diffraction reveals one-dimensional chain structures composed of square antiprismatic NpO8polyhedra linked via four trigonal pyramidal SeO3and HSeO3units. Raman spectral analysis supports the presence of both selenite and hydroselenite due to the presence of corresponding modes within the spectra. The addition of selenic acid to a NpVstock solution resulted in the precipitation of elongated rose prisms of K2[(NpO2)2(SeO4)3(H2O)2]·(H2O)1.5(2), Rb2[(NpO2)2(SeO4)3(H2O)2]·(H2O)2(3) and K9[(NpO2)9(SeO4)13.5(H2O)6]·(H2O)12(4) as well as light red plates of Cs2[(NpO2)2(SeO4)3] (5). To our knowledge, this is the first report of NpVIselenates. All four structures show two-dimensional layered structures with alkali cations acting as charge balancing counter cations. Hereby the layers of compounds 2and 3are found to be orientational geometric isomers. Distinctly different phenomena are made responsible for the phase formation within these systems. The kinetically driven process of NpVdisproportionation led to the formation of the NpIVselenites in the SeIV-based system, whereas the oxidation of NpVby reduction of nitrate in acidic conditions is responsible for the formation of the NpVIselenates in the SeVIsystem. The influence of air oxygen is also discussed for the latter reaction.

Studies of transuranic organometallic complexes provide a particularly valuable insight into covalent contributions to the metal–ligand bonding, in which the subtle differences between the transuranium actinide ions and their lighter lanthanide counterparts are of fundamental importance for the effective remediation of nuclear waste. Unlike the organometallic chemistry of uranium, which has focused strongly on UIIIand has seen some spectacular advances, that of the transuranics is significantly technically more challenging and has remained dormant. In the case of neptunium, it is limited mainly to NpIV. Here we report the synthesis of three new NpIIIorganometallic compounds and the characterization of their molecular and electronic structures. These studies suggest that NpIIIcomplexes could act as single-molecule magnets, and that the lower oxidation state of NpIIis chemically accessible. In comparison with lanthanide analogues, significant d- and f-electron contributions to key NpIIIorbitals are observed, which shows that fundamental neptunium organometallic chemistry can provide new insights into the behaviour of f-elements.

Several N‐benzylnitrones reacted with carbon dioxide in the presence of samarium(II) iodide leading to α‐amino acids as the products of reductive C–C coupling. The best selectivities were observed at a carbon dioxide pressure of 50 bar at ambient temperature. The influences of different functional groups in the nitrone backbone and of the coordinating additives to samarium(II) iodide on the product distribution were investigated. The racemic α‐amino acids were obtained in up to 70 % yield based on HPLC data.

Several penta‐ and hexaalkylated guanidinium‐based ionic liquids (GILs) were tested as solvents for the epoxidation of cyclooctene using the Venturello catalyst, [(C8H17)3N(CH3)]3[PO4{WO(O2)2}4], and hydrogen peroxide as the oxidant. Epoxide yields were obtained in a broad range between 13 and 79 % depending on both the anion and the substituents on the guanidinium moiety. Recycling experiments showed that the catalyst can be used at least three times. Furthermore, new guanidinium phosphotungstates with the PW12O403–anion were synthesized and characterized. Their catalytic performance was evaluated, and GILs as well as acetonitrile were employed as the solvent. Results were compared to those obtained with the comparable ammonium‐based catalysts [NR4]3[PW12O40] (R = C4H9, C6H13) and the analogous imidazolium‐based catalyst [BMIM]3[PW12O40] containing the 1‐butyl‐3‐methylimidazolium cation. Employing different GILs as solvents, similar results were obtained for the guanidinium and imidazolium catalysts but significantly lower epoxide yields were obtained using the ammonium catalysts. On using acetonitrile as the solvent, guanidinium‐based catalysts exhibited a better performance than the imidazolium catalyst in the case of linear and branched olefins and vice versa in the case of cyclic olefins.

The synthesis and characterization of the new octanuclear mixed carbamate complex [Zn2Mn6(μ4‐O)2(O2CN(iPr)2)12] is reported. This complex is readily oxidized by O2to give [Zn2Mn6(μ4‐O)2(μ3‐O)(O2CN(iPr)2)12] featuring a central O atom statistically distributed over two sites within the void of the inner Mn6cage of the carbamate complex. In relation to the situation before oxidation, the metal cage is expanded by a change of the carbamate bonding mode. The two carbamate complexes were used as precursors to magnetic oxide nanoparticles under mild conditions (210–270 °C depending on the heating rate). A mixture of crystalline ZnMn2O4and MnO nanoparticles resulted. The experimental data are complemented by some quantum chemical (DF) calculations.

Tetrameric Zn alkyl carbamates [ZnR(O2CNR′2)]4(R = Me or Et, R′ = iPr) have been synthesized from alkylzinc amides and CO2. The reaction of these carbamates with specially designed CoIIcomplexes afforded new heterobimetallic (Zn/Co) carbamate complexes. The thermal decomposition of these single‐source precursors under mild conditions (200–300 °C) led to magnetic mixed‐metal oxide nanoparticles. Two phases were identified that are isostructural with ZnO (wurtzite phase) and CoO (cubic rock salt structure), but both contain Zn and Co in varying molar ratios. The particles with the ZnO‐type structure have a mean average size of 7.7 nm, whereas the particles with the CoO‐type structure are much larger (ca. 48 nm).

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Lanthanoid‐artig: Röntgenbeugung und DFT‐Studien ergaben, dass die Ionen [An(H2O)9]3+der Actinoide U3+–Cf3+in Kristallen ihrer Triflatsalze dieselbe Struktur und elektrostatische Bindung wie ihre Lanthanoid‐Gegenstücke La3+–Eu3+aufweisen. Zudem zeigte sich, dass die Neunfachkoordination in Lösung bei den leichteren Elementen weitgehend erhalten ist (siehe Bild).

The absorption spectrum of tris[hydrotris(1‐pyrazolyl)borato]uranium(III) (UTp3) was run at room and low temperatures. From the spectra obtained, a truncated crystal field (CF) splitting pattern could be derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian achieving an r.m.s. deviation of 37.7 cm–1for 29 assignments. The parameters used allow the insertion of the Tp ligand into empirical spectrochemical, nephelauxetic and relativistic nephelauxetic series of UIIIcompounds, and the set‐up of experimentally based nonrelativistic and relativistic molecular orbital schemes of UTp3in the f range. Using the wavefunctions and eigenvalues of the fit, the experimentally determined temperature dependence (in the range 1.34–294.4 K) of μ2effcould be reproduced adopting an orbital reduction factor k = 0.99.

Herein we report on CO2fixation by insertion into the Zn–N bonds of the two molecular compounds EtZnNiPr2and EtZnNiBu2. The tetrameric carbamate complexes [EtZnO2CNR2]4R = iPr and iBu were found to be the products of these reactions. The structures of the complexes were established by singlecrystal Xray diffraction. Thermal decomposition of the carbamate complexes was studied by applying a variety of different analytical techniques. These studies show that the compounds are suitable precursors for nanosized ZnO particles of ca. 10 nm diameter synthesised under mild conditions < 200 °C with the oxygen atoms originating from the reactant CO2. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008

10Ethyl9oxa10phosphaphenanthrene10oxide 1 can be nitrated using acetic anhydride and fuming nitric acid. The nitro group is reduced using palladium on charcoal and hydrogen. These reaction conditions are used for the synthesis of an analogous DOPObased diaminic hardener 7. An evaluation of the curing behavior, mechanical properties and flammability of a neat resin made of DGEBA and 7DGEBA  7 and of a carbon fiberreinforced resin made of DGEBA, 4,4′diaminodiphenylsulfon DDS and 7DGEBA  DDS  7 shows the potential of this hardener to lead to flameretardant systems while keeping relevant properties on a high level; especially when compared to a similar system DGEBA  DDS  1.

Ruthenium complexes, mer‐[RuX3(MeCN)3] and cis/trans‐[RuX2(MeCN)4] with X=Br, Cl, were investigated as precatalysts in homogeneously catalyzed hydrosilylation of CO2. The oxidation state of ruthenium and nature of the halide in the precatalysts were found to influence the catalytic activity in the conversion of Me2PhSiH to the formoxysilane Me2PhSiOCHO, with RuIIIhaving chloride ligands being most active. Monitoring the reactions by in‐situ IR spectroscopy in MeCN as the solvent indicates an interaction of the precatalyst with the silane prior to activation of CO2. In the absence of CO2, hydrosilylation of the MeCN solvent occurs. Catalytic activity in CO2hydrosilylation is enhanced by Me2PhSiCl, generated during reduction of RuIIIin mer‐[RuX3(MeCN)3] to RuIIor, when added as promoter to RuIIprecatalysts. The reaction mechanism for the catalytic cycle has been calculated by DFT methods for the reaction of Me3SiH. The key steps are: Transfer of the Me3Si moiety to a coordinated halide ligand, resulting in an LnRuH(XSiMe3) intermediate → CO2coordination → Me3Si transfer to CO2→ reductive elimination of formoxysilane product. This reaction sequence is more favorable energetically for chloride complexes than for the analogous bromide complexes, which accounts for their differences in catalytic activity. Calculations also explain the rate increase observed experimentally in the presence of Me2PhSiCl. A parallel reaction pathway leads to (Me3Si)2O as a minor byproduct which arises from the condensation of two initially formed Me3SiOH molecules.

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N,N,N′,N′-Tetrakis(2-pyridylmethyl)benzene-1,3-diamine (1,3-tpbd), a bis(tridentate) ligand, its protonated derivative, [1,3-tpbdH2]2+, and a series of new dinuclear complexes [Fe2(1,3-tpbd)(CH3CN)6](ClO4)4·(CH3CN)2·(H2O)0.5 (1), [Fe2(1,3-tpbd)(DMF)6](ClO4)4 (2), [Ni2(1,3-tpbd)(DMF)6](ClO4)4 (3), [Zn2(1,3-tpbd)(CH3CN)2(SO3CF3)2(H2O)](SO3CF3)2 (4), [Zn2(1,3-tpbd)Cl4]·H2O (5), [CuZn(1,3-tpbd)Cl4] (7) and the tetranuclear copper(II) complex [Cu2(1,3-tpbd)2(H2O)2](ClO4)4·2H2O (8) have been prepared and structurally characterized. Complex 8, a so called “dimetallocyclophane”, interestingly only formed in the presence of zinc ions and not when copper(II) ions were mixed stoichiometrically (1:1 mixtures) under aerobic conditions. Theoretical calculations provide evidence for the formation of a side-on dinuclear peroxido copper complex during the oxidation of the (1,3-tpbd)copper(I) complex. A possible reaction product, the dinuclear copper complex [Cu2(2,6-tpcd)(H2O)(Cl)](ClO4)2·2H2O (9) of a phenolate derivative of 1,3-tpbd was synthesized and structurally characterized independently from oxidation reactions from copper(II) perchlorate and the ligand 2,6-bis[bis(2-pyridylmethyl)amino]-p-cresol. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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Electronic Structures of Organometallic Compounds of f Elements. 64 Does the Zwitterionic Nature of the Triphenylphosphine Oxide Ligand Manifest itself in its Spectrochemical Properties?

For the alternating copolymerization of CO2 and cyclohexene oxide, a variety of zinc acetate complexes with new aminoimidoacrylate ligands has been synthesized and tested as catalysts. All complexes catalyzed the reaction and structure-activity investigations revealed that the highest activities and selectivities were reached when the ligand’s aromatic rings were 2,6-substituted by alkyl groups of different size (isopropyl versus methyl) and when the ligand backbone embodied an electron-withdrawing cyano group. Furthermore, these complexes catalyzed the terpolymerization of CO2, cyclohexene oxide and lactide to give poly(cyclohexyl carbonate-co-lactide) and the composition of the polymer was adjustable by the monomer feed.

Electronic Structures of Organometallic Compounds of f Elements. 63 Parametric Analysis of the Crystal Field Splitting Pattern of Pseudo Trigonal Planar Er(η5‐C5H4tBu)3

During lab-scale experiments on the reforming of methanol by means of water at supercritical conditions (T > 374°C, p > 22.1 MPa), a tubular reactor with a titanium liner was exposed to an aqueous solvent containing methanol (5 wt%) and KHCO3 (0.3 wt%). At the end of the run, a fibrous precipitate was found at two positions in the reactor. The material was studied in a field emission scanning electron microscope equipped with an energy dispersive X-ray analysis unit (FESEM/EDX). A thin-film support technique using carbon-filmed TEM grids was applied to perform scanning transmission-type imaging (STEM-in-SEM operation) and transmission current measurements. The analysis of the hydrothermally grown fibers resulted in a potassium titanate species composed of approximately K2TiO3, which has been confirmed by X-ray diffraction (XRD).

Electronic Structures of Highly Symmetrical Compounds of f Elements. 40. Parametric Analysis of the Crystal Field Splitting Pattern of Tris(hydrotris(1‐pyrazolyl)borato)neodymium(III)

Synthesis and structural characterization of the iron(III) complexes of the tripodal ligands N′,N′-bis[(2-pyridyl)methyl]ethylenediamine (uns-penp), [Fe(uns-penp)Cl2]ClO4·CH3CN, [{Fe(uns-penp)Cl}2O](ClO4)2·2CH3CN and the amide derivative N-Acetyl-N′,N′-bis[(2-pyridyl)methyl]ethylenediamine (acetyl-uns-penp), [Fe2(acetyl-uns-penp)2O](ClO4)2·H2O, [Fe(acetyl-uns-penp)(tcc)Br]·(C2H5)2O (tcc = tetrachlorocatecholate), and [{Fe(acetyl-uns-penp)(tcc)}2O]·(C2H5)2O·CH3OH are reported. Catechol dioxygenase reactivity of in situ prepared complex solutions was tested and showed that all complexes reacted slower compared with the iron tmpa system described in the literature. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The reaction of carbon dioxide with the stannane nBu2Sn(OiPr)2and distannoxane [nBu2(iPrO)Sn]2O leads to the selective insertion into one Sn–OiPr bond generating the corresponding nBu2Sn(OiPr)(OCO2iPr) and nBu2(iPrO)SnOSn(OCO2iPr)nBu2species. Both compounds are characterised by multinuclear NMR, FT-IR and single-crystal X-ray crystallography. In the solid state, they adopt a dimeric arrangement with bridging isopropoxy and terminal isopropylcarbonato ligands. The X-ray crystal structure of the dinuclear stannane shows that the Sn2O2ring and the two Sn–OCO2C fragments are nearby coplanar. The same holds for the ladder-type tetranuclear distannoxane. The dimeric structures are also evidenced by solution NMR in non-coordinating solvents. Interestingly, the assignment of the exoand endotin resonances of the dimeric distannoxane is unambiguous using a labeled 13CO2experiment. The stability of the dimeric association has been probed in the stannane series on the basis of DFT calculations.

New 3-amino-2-cyanoimidoacrylate ligands with varying steric demands have been synthesized. Zinc acetate complexes of these ligands catalyze the copolymerisation of CO2 and cyclohexene oxide, showing high activities (TOF up to over 200 4;h−1).

Electronic Structures of Highly Symmetrical Compounds of f Elements. 38 [1] Crystal, Molecular and Electronic Structure of Tris(hydrotris(1‐pyrazolyl)borato)samarium(III)

[Ln(Cp)3(OP(OR)3)] (Cp = η5‐Cyclopentadienyl; Ln = La, R = Et (1); Ln = Pr, R = Me (2); Ln = Pr, R = Et (3)) und [Pr(Ind)3(OP(OEt)3)] (4) wurden synthetisiert und spektroskopisch sowie teilweise strukturell (nur Verbindungen 1und 2) charakterisiert. Auf der Grundlage der bei variablen Temperaturen aufgenommenen α‐Absorptionsspektren eines orientierten Einkristalls, der magnetischen Zirkulardichroismusspektren von gelöstem, und der Lumineszenzspektren von gepulvertem Material konnte ein fast vollständiges Kristallfeld(KF)‐Aufspaltungsmuster von 3aufgestellt und durch Anpassung der freien Parameter eines phänomenologischen Hamilton‐Operators simuliert werden. Die hierbei verwendeten Parameter erlaubten die Berechnung der vom Pr3+‐Zentralion wahrgenommenen globalen KF‐Stärke, die Abschätzung der nephelauxetischen und relativistischen nephelauxetischen Parameter, sowie die Aufstellung der experimentorientierten nichtrelativistischen und relativistischen Molekülorbital‐Schemata im f‐Bereich. Die optischen Spektren von Verbindung 4weisen auf die Existenz zweier unterschiedlicher Spezies bei tiefen Temperaturen hin, wodurch eine erfolgreiche KF‐Analyse der Spektren verhindert wird.

The synthesis and characterisation of Rubipy2L12and the homodinuclear complexes Mbipy2L1Mbipy24where M Ru or Os, employing the ditopic ligand, 1,4-phenylene-bis1-pyridin-2-ylimidazo1,5-apyridine L1, are reported. The complexes are identified by elemental analysis, UVVis, emission, resonance Raman, transient resonance Raman and 1H NMR spectroscopy, mass spectrometry and electrochemistry. The X-ray structure of the complex Rubipy2L1bipy2RuPF64is also reported. DFT calculations, carried out to model the electronic properties of the compounds, are in good agreement with experiment. Minimal communication between the metal centres is observed. The low level of ground state electronic interaction is rationalized in terms of the poor ability of the phenyl spacer in facilitating superexchange interactions. Using the electronic and electrochemical data a detailed picture of the electronic properties of the RuRucompound is presented.

Pr(OAr′)3 und Nd(OAr′)3 kristallisieren (bei ca. 150 K bzw. 200 K) in der monoklinen Raumgruppe P21mit vier Molekülen pro Elementarzelle. Betrachtet man lediglich die unmittelbar koordinierten Sauerstoffatome, dann ist das effektive Kristallfeld von C3v‐Symmetrie. Die Signale in den optischen Spektren von Pr(OAr′)3sind selbst bei 80‐90 K sowohl bei Verwendung von Lösungen als auch von Festkörpern ungewöhnlich breit, so daß sie sich nicht für Interpretationszwecke eignen. Nd(OAr′)3 weist dagegen sowohl bei Raumtemperatur als auch bei tiefen Temperaturen scharfe Absorptionsbanden auf, die in Analogie zu den bereits früher auf der Grundlage optischer Polarisationsmessungen identifizierten Absorptionsübergängen von Nd[N(SiMe3)2]3zugeordnet werden. Das so abgeleitete Kristallfeld‐Aufspaltungsmuster wird durch Anpassung der offenen Parameter eines phänomenologischen Hamilton‐Operators simuliert, wobei eine reduzierte r.m.s.‐Abweichung von 26.4 cm—1bei 64 Zuordnungen erzielt wurde. Die dabei verwendeten Parameter gestatten die Bestimmung der Ligandenfeldstärke des (OAr′)—‐Liganden, die Einreihung dieses Liganden in empirische nephelauxetische und relativistische nephelauxetische Reihen und die Aufstellung experimentorientierter nichtrelativistischer und relativistischer Molekülorbital‐Schemata im f‐Bereich.

To investigate whether generation and liberation of bradykinin and histamine contribute to generalized edema formation in pediatric cardiopulmonary bypass surgery.

Synthesis and structural characterization of the copper(i) and copper(ii) complexes of the tripodal tetradentate ligand (2-aminoethyl)bis(2-pyridylmethyl)amine (uns-penp) are reported as well as the reactivity of the copper(i) uns-penp complex towards dioxygen. Uns-penp can be easily modified and two copper(ii) complexes of these derivatives have been structurally characterized. In the copper(ii) complex of an amide derivative of uns-penp, [Cu(acetyl-uns-penp)Cl]ClO₄, it is evident that the amide nitrogen is no longer truly sp2 hybridised, a consequence of a weak interaction with the copper(ii) ion.

Synthesis and structural characterization of the copperi and copperii complexes of the tripodal tetradentate ligand 2-aminoethylbis2-pyridylmethylamine uns-penp are reported as well as the reactivity of the copperi uns-penp complex towards dioxygen. Uns-penp can be easily modified and two copperii complexes of these derivatives have been structurally characterized. In the copperii complex of an amide derivative of uns-penp, Cuacetyl-uns-penpClClO4, it is evident that the amide nitrogen is no longer truly sp2hybridised, a consequence of a weak interaction with the copperii ion.

The synthesis, purification and characterisation of two coordination isomers of ruthenium(ii) and osmium (ii) complexes containing the ligand 3-(pyrazin-2'-yl)-5-(pyridin-2"-yl)-1,2,4-triazole (Hppt) are described. The X-ray and molecular structure of the complex [Ru(bipy)₂(ppt)]PF₆·CH₃OH (1a) is reported, where the Ru(bipy)₂-centre is bound to the ppt− ligand via the pyridine nitrogen and the N1 atom of the triazole ring. 1H NMR spectroscopic measurements confirm that in the second isomer (1b) the Ru(bipy)₂-moiety is bound via the N2 atom of the triazole ring and the pyrazine ring. Partially deuteriated metal complexes are utilised to facilitate interpretation of 1H NMR spectra. The redox and electronic properties indicate that there are significant differences in the electronic properties of the two coordination isomers obtained. The acid–base properties of the compounds are also reported and show that the pK_a of the 1,2,4-triazole ring varies systematically depending on the nature of the non-coordinating substituent. Analysis of these data indicates a significant electronic interaction between the pyridyl/pyrazyl rings and the 1,2,4-triazole ring in the coordinated ppt− ligand.

Im Gegensatz zum Ergebnis einer früheren Lumineszenzmessung, aber in Übereinstimmung mit früheren IR‐ und FIR‐spektroskopischen Befunden hat Tris(hydrotris(1‐pyrazolyl)borato)europium(III) (EuTp3) gemäß dem Ergebnis einer Einkris tall‐Röntgenstrukturanalyse eine Struktur, bei der das Eu3+‐Zentralion in erster Koordinationssphäre von neun N‐Atomen in Form eines dreifach überkappten trigonalen Prismas koordiniert ist, so daß ein effektives Kristallfeld(KF) der Symmetrie D3hresultiert. Betrachtet man jedoch das Gesamtmolekül, so liegt im Kristall molekulare C3h‐Symmetrie vor. Dasselbe gilt für den entsprechenden La‐Komplex. Das Absorptionsspektrum von gepulvertem EuTp3wurde bei ca. 5 K, und das Lumineszenzspektrum bei ca. 77 K vermessen. Den optischen Spektren wurde ein partielles KF‐Aufspaltungsmuster entnommen, das eine Sequenz von Energieniveaus von Γ4‐ und Γ6‐Symmetrie umfaßt. Vorzeichen und Betrag des KF‐Parameters B02wurden auf experimenteller Basis abgeleitet, und Modellrechnungen auf der Grundlage der Näherungen des elektrostatischen Punktladungsansatzes und des angular overlap‐Modells führen jeweils zu negativen KF‐Parametern B04und B06. Unter Beachtung dieser berechneten Vorzeichen konnte das experimentell bestimmte partielle KF‐Aufspaltungsmuster von EuTp3durch Anpassung der offenen Parameter eines phänomenologischen Hamilton‐Operators simuliert werden.

Aromatic interactions are well known to participate in the structural stabilization of biological macromolecules. We have utilized this motif as an unconventional new means to control the stereochemistry of synthetic zinc complexes. The aromatic amino acid l-phenylalanine has been applied as a building block in the chiral ligand bpaAc–Phe–OMe (N,N-bis(2-picolyl)aminoacyl-(S)-phenylalanine-methylester). Zinc(ii) complexes of this ligand are always trigonal–bipyramidal in the solid state. This is confirmed by the X-ray structures of [(bpaAc–Phe–OMe)Zn(OTf)]+ (1b, OTf = Triflate), [(bpaAc–Phe–OMe)Zn(H₂O)]2+ (2b), and [(bpaAc–Phe–OMe)Zn(pz)]2+ (3b). In contrast, the octahedral complexes [(bpaAc–Gly–OEt)Zn(pz)(OTf)]+ (3a) and [(bpaAc–Gly–OEt)Zn(N-Meim)(H₂O)]2+ (4a) have been obtained with the related glycine derived ligand bpaAc–Gly–OEt. A comparison with the five-coordinate structures of [(bpaAc–Gly–OEt)Zn(OTf)]+ (1a) and [(bpaAc–Gly–OEt)Zn(Cl)]+ (5) allows an appreciation of effects brought about by (1) the coligand (chloride, triflate, pyrazole, N-methylimidazole) and (2) the non-coordinating amino acid side chain (benzyl in bpaAc–Phe–OMe). It is shown that the pyrazole complex 3b adopts an unusual tense five-coordinate geometry which is stabilized by weak aromatic interactions. The structure represents an analogue of the possible transition state between five-coordinate trigonal-bipyramidal and six-coordinate octahedral complexes in our series.

A series of copper(II) complexes containing the amino acid derived ligands bpaAc-Gly-OEt {1; [bis(picolyl)amino]acylglycine ethyl ester} and bpaAc-Phe-OMe {2; [bis(picolyl)amino]acylphenylalanine methyl ester} were synthesized and characterized in solution and in the solid state. This was done in order to evaluate the relevance of weak aromatic interactions between a metal center and amino acid side chains in square-pyramidal or octahedral coordination environments. The results showed that the structural, spectroscopic, and electrochemical properties of the copper(II) center are not affected by the amino acid side chain structure. This is in remarkable contrast to our previous investigations on zinc(II) complexes of the same ligands, which indicate close association of the metal center and the phenyl substituent of 2 in a trigonal-bipyramidal environment. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Bi- and tetranuclear zinc complexes of the tridentate N,N,O ligand [{[2-(2-pyridyl)ethyl]imino}methyl]phenol (HL) and their enzyme-like reactions are described. The coordinated water molecules in a dizinc complex of this ligand can be deprotonated reversibly similar to those in the resting states of zinc enzymes. The resulting tetranuclear complex bearing bridging hydroxide ions allows the reversible uptake of CO2. Whereas the coordination of hydrogen carbonate has not been observed, a tetranuclear carbonate complex with a unique structure was isolated. Its carbonate ion is coordinated to all four zinc atoms. The X-ray structures of the reported complexes are discussed. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

The two new ligands N-[(2-pyridyl)methyl]-2,2'-dipyridylamine (L1) and N-[bis(2-pyridyl)methyl]-2-pyridylamine (L2) have been synthesized and the copper(II) complexes [Cu(L1)2(CH3OH)2](ClO4)2, [Cu(L1)2(H2O)2](ClO4)2, [Cu3(L1)2(DMF)2Cl6], [Cu(L1)Cl2]n, [Cu(L2)(Cl)(ClO4)], and [Cu(L2)Cl2] have been structurally characterised. The reactions of dioxygen with the copper(I) complexes with ligands L1 and L2 were investigated, but no copper−dioxygen intermediates could be detected spectrophotometrically.

Dicyanomethanides, [RC(CN)2]⁻ (1⁻), are bridging ligands with an angular clamp-type shape. In the tripod/iron(II) system, [tripod = CH3C(CH2PPh2)3], they form binuclear species with three of the clamp-type ligands bridging two iron centers. An appropriate stoichiometric mixture of the tripod ligand, iron(II) salts and the dicyanomethanide ligand leads to the exclusive formation of [tripodFe{μ-NC−C(R)−CN}3Fetripod]⁺ (3⁺). Altogether, seven constituent groups arrange themselves in this type of aggregate. The process of self-aggregation is distinctly modified by the presence of cyanide ions that may act as linear rod-type bridging ligands. Equimolar mixtures of tripod, iron(II) salts, dicyanomethanide ligands and cyanide form tetranuclear aggregates [{tripodFe}3{μ-NC−C(R)−CN}3{μ-CN}3FeX]⁺ (5⁺). In these species, the iron centers form a trigonal-pyramidal arrangement with three octahedrally coordinated low-spin tripodiron(II) entities in the basal plane and a tetrahedrally coordinated high-spin iron(II) at the apex. The iron centers in the basal plane are connected by μ²-bridging dicyanomethanide ligands. The apical iron center is coordinated by the N-termini of three cyano ligands, which complete the octahedral coordination of the basal low-spin iron(II) centers. The fourth, external ligand X at the tetrahedrally coordinated high-spin iron(II) apex can be varied, but in most cases it is found to be a terminally coordinated dicyanomethanide entity. Without counting this variable ligand X, thirteen constituent groups of four different types selectively aggregate to form the cage compounds 5⁺. While the dinuclear compounds 3⁺ are diamagnetic, the tetranuclear species 5⁺ have magnetic moments close to the spin-only value of μs.o. = 4.9 μB, for tetrahedral high-spin iron(II). The Mössbauer spectra are in agreement with the description of 5⁺ above, which contain three low-spin tripodiron(II) entities and one high-spin iron(II) center. The synthesis, spectroscopic data, cyclic voltammetric data, Mössbauer data and X-ray analytical data for a series of compounds of types 3⁺ and 5⁺ are presented in this paper.

A series of three new quadridentate ligands was synthesized by reaction of the haloacetylated amino acid esters L-BrAc−Phe−OMe (4a), L-BrAc−Lys(Z)−OMe (4b), and ClAc−Gly−OEt (4c), respectively, with bis(picolyl)amine (bpa, 5). The obtained products L-bpaAc−Phe−OMe (3a), L-bpaAc−Lys(Z)−OMe (3b), and bpaAc−Gly−OEt (3c) were treated with Zn(OTf)2 (OTf = CF3SO3⁻) to yield the trigonal-bipyramidal complexes [(L-bpaAc−Phe−OMe)ZnOTf](OTf) (6a), [(L-bpaAc−Lys(Z)−OMe)ZnOTf](OTf) (6b), and [(bpaAc−Gly−OEt)ZnOTf](OTf) (6c). Crystal structures of 6c and the hydrolysis product [(L-bpaAc−Phe−OMe)(H2O)ZnOTf](OTf)2 (7a) are reported. The results suggest the formation of a chiral pocket at the metal center provided by the benzyl substituent in the L-phenylalanine derivative 7a. This observation is further supported by ¹H-NMR and circular dichroism spectroscopic data. These methods indicate a significant ordering effect within the ligands upon metal coordination as well as interactions between the first coordination spheres and their chiral environments provided by the L-phenylalanine and L-lysine moieties of 3a and 3b, respectively. Our results are discussed with respect to the development of chiral building blocks for transition metal catalysts and biomimetic assemblies.

When in contact with oxidizing media, UO2pellets used as nuclear fuel may transform into U4O9, U3O7, and U3O8. The latter starts forming by stress-induced phase transformation only upon cracking of the pristine U3O7and is associated with a 36% volumetric expansion with respect to the initial UO2. This may pose a safety issue for spent nuclear fuel (SNF) management as it could imply a confinement failure and hence dispersion of radionuclides within the environment. In this work, UO2with different grain sizes (representative of the grain size in different radial positions in the SNF) was oxidized in air at 300 °C, and the oxidation mechanisms were investigated using in situ synchrotron X-ray diffraction. The formation of U3O8was detected only in UO2pellets with larger grains (3.08 ± 0.06 μm and 478 ± 17 nm), while U3O8did not develop in sintered UO2with a grain size of 163 ± 9 nm. This result shows that, in dense materials, a sufficiently fine microstructure inhibits both the cracking of U3O7and the subsequent formation of U3O8. Hence, the nanostructure prevents the material from undergoing significant volumetric expansion. Considering that the peripheral region of SNF is constituted by the high burnup structure, characterized by 100–300 nm-sized grains and micrometric porosity, these findings are relevant for a better understanding of the spent nuclear fuel behavior and hence for the safety of the nuclear waste storage.

The spectroscopic and electrochemical properties of a series of dinuclear mixed-valence complexes containing two (triphos)Co units are reported: [(triphos)Co(L)Co(triphos)]⁺ (L = C6O4X2; X = H, Cl, Br, I, Me: 2a–e⁺; L = C14H4O4Me2: 4⁺). Complexes 2a–e⁺ are bridged by tetraoxybenzene ligands and exhibit very strong metal–metal interaction leading to delocalized class-III behaviour while in 4⁺ the extended tetraoxoanthracence bridging ligand leads to a partial electron localization. Additionally, the different oxidation behaviour of the parent dicationic complexes 1a–e²⁺ and 3²⁺ have been investigated and are explained on the basis of a qualitative MO model.

The authors compare the performance of high-field and low-field magnetic resonance (MR) systems in the evaluation of shoulder instability, 35 patients were examined at field strengths of 1.0 T and of 0.2 T.

The tripodal triphosphide H3CC[CH2P(Ph)(Li)]3 reacts with MeSiCl3 to yield the triphosphinosilane H3CC[CH2P(Ph)]3SiMe, 2a. The analogous reaction with PBr3 produces the triphosphinophosphine H3CC[CH2P(Ph)]3P, 2b. The bicyclo[2.2.2]octane-type cage structure of 2 is revealed by NMR data as well as X-ray analyses. 2b is one of the rare examples of a compound with mere C3-symmetry.

Several ways to functionalize hydroxy-tripod-ligands (HOCH2C(CH2PR2)3) by activation with electrophiles are presented. The use of carboxylic halides and anhydrides is shown to be generally successful for esterification reactions in a one-pot synthesis starting from the oxetanes O(CH2)2C(CH2PR2)2. Facial coordinaton of the related esters towards iron(II) and molybdenum(O) can be achieved depending on the nature of the phosphane donor groups.