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A variety of 4‐phosphinylpyrrolidin‐3‐ones was prepared via a [3+2] cycloaddition between aryl aldonitrones and phosphinylallenes. The products were isolated as unique 4,5‐trans diastereomers, in yields between 47% and 80%, over 23 examples. In the case of chiral racemic allenes, a 2:1 to 4:1 moderate 2,5‐diastereoselectivity was observed. Under the reaction conditions, the cycloadducts directly undergo a rearrangement to afford selectively the corresponding pyrrolidin‐3‐ones. DFT calculations provide some insights into the mechanism, involving the homolytic cleavage of the N−O bond of the cycloadduct. [ABSTRACT FROM AUTHOR]

Dinuclear transition metal complexes with direct metal–metal interactions have the potential to generate unique reactivities and properties. Using asymmetric triazine ligands HN3tBuR (R = Et, iPr, nBu) featuring different alkyl substituents at 1,3-N centers, we report here the first rational synthesis of 'tetragonal lantern' type Fe(II) triazenides [Fe2(N3tBuR)4] [R = Et (1), iPr (2), nBu (3)] having an exceptionally short Fe–Fe distance (2.167–2.174 Å). Unlike the previously reported lantern structures with related amidinate or guanidinate ligands, highly air-sensitive 1–3 show a lower spin ground state, as indicated by Mössbauer, 1H NMR and DFT studies. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure of various complexes of pentavalent uranyl species, namely UO2 +, is described, using DFT methods, with the aim of understanding how the structure of the ligands may influence the localisation of the unpaired 5f electron of uranium (V) and, finally, the stability of such complexes towards oxidation. Six complexes have been inspected: [UO2py5]+ (1), [(UO2py5)KI2] (2), [UO2(salan-tBu2)(py)K] (3), [UO2(salophen-tBu2)(thf)K] (4), [UO2(salen-tBu2)(py)K] (5), [and UO2-cyclo[6]pyrrole]1− (6), chosen to explore various ligands. In the five first complexes, the UO2 + species is well identified with the unpaired electron localized on the 5f uranium orbital. Additionally, for the salan, salen and salophen ligands, some covalent interactions have been observed, resulting from the presence of both donor and acceptor binding sites. In contrast, the last complex is best described by a UO2 2+ uranyl (VI) coordinated by the anionic radical cyclopyrrole, the highly delocalized π orbitals set stabilizing the radical behaviour of this ligand. [ABSTRACT FROM AUTHOR]

A description of the electronic structure of F3UCO, F3NdCO, F4UCO, and F5UCO has been obtained by Complete Active Space second-order perturbation theory CASPT2 calculations using a relativistic effective core potential. These multiconfigurational calculations have been compared to the DFT description combined with a quasi-relativistic ZORA scalar approach. Geometries have been optimized for both levels of calculations and frequencies computed in the DFT formalism. The bonding properties of U(III) have been compared to those of Nd(III) and of higher oxidation states of U(IV,V). Both methodologies are consistent and show a decrease of the covalent character of the U−CO bonding with a higher oxidation state, U(IV) or U(V), as well as its absence for for the isoelectronic Nd(III) species. [ABSTRACT FROM AUTHOR]

Abstract: The quantum chemical study presented here shows various aspects of the bonding of lanthanide (La3+, Gd3+) and actinide (U3+, Am3+, Cm3+) ions with N-heterocyclic ligands (polyazines, BTP: bis(1,2,4-triazinyl)-2,6-pyridine). Several families of complexes, differing by their coordination sphere, have been examined. Clearly, the lanthanide complexes always show a purely ionic bonding. The behaviour of U(III) is also well defined with a more or less strong backbonding interaction whatever the complex is. In contrast, the heavy actinides (Am3+ and Cm3+) are changeable, with a weak covalent character, going from donation to backdonation, depending on the coordination sphere of the complex. [Copyright &y& Elsevier]

A comparative density functional study on metal–ligand (M–L) interaction has been performed on X3–M–L (X = F, I; M = U, La, Nd: L = NH3, NCCH3, CO) and X3–M–(CO)2 species including scalar relativistic effects by means of the zero-order regular approximation (ZORA) hamiltonian. The role of the halogen atoms in modeling the M–L interactions is discussed for π-acceptor ligands CO and NCCH3 and for the σ-donor NH3. The fluoride counterions, compared with previous calculations on the iodide complexes, stabilize more tedraedral structure with longer M–L distances. Finally, the addition of a second ligand to the previous species has permitted a more complete discussion on the backbonding effects on the uranium complexes. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [ABSTRACT FROM AUTHOR]

This article describes a density functional theory (DFT) study to explore a bio‐inspired NiFe complex known for its experimental activity in electro‐reducing CO2 to CH4 when adsorbed on graphite. The coordination properties of the complex are investigated in isolated form and when physisorbed on a graphene surface. A comparative analysis of DFT approaches for surface modeling is conducted, utilizing either a finite graphene flake or a periodic carbon surface. Results reveal that the finite model effectively preserves all crucial properties. By examining predicted structures arising from CO2 insertion within the mono‐reduced NiFe species, whether isolated or adsorbed on the graphene flake, a potential species for subsequent electro‐reduction steps is proposed. Notably, the DFT study highlights two positive effects of complex adsorption: facile electron transfers between graphene and the complex, finely regulated by the complex state, and a lowering of the thermodynamic demand for CO2 insertion. [ABSTRACT FROM AUTHOR]

The molecular doping of graphene with π-stacked conjugated molecules has been widely studied during the last 10 years, both experimentally or using first-principle calculations, mainly with strongly acceptor or donor molecules. Macrocyclic metal complexes have been far less studied and their behavior on graphene is less clear-cut. The present density functional theory study of cobalt porphyrin and phthalocyanine adsorbed on monolayer or bilayer graphene allows to compare the outcomes of two models, either a finite-sized flake of graphene or an infinite 2D material using periodic calculations. The electronic structures yielded by both models are compared, with a focus on the density of states around the Fermi level. Apart from the crucial choice of calculation conditions, this investigation also shows that unlike strongly donating or accepting organic dopants, these macrocycles do not induce a significant doping of the graphene sheet and that a finite size model of graphene flake may be confidently used for most modeling purposes. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from FeII and FeIII precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV‐visible, Mössbauer), ESI‐MS and DFT studies, an FeIV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the FeII precursor was expected by a two‐electron oxidative addition, its formation from an FeIII precursor was unprecedented. Thanks to a combination of spectroscopic (UV‐visible, EPR, Hyscore and Mössbauer), ESI‐MS and DFT studies, we found that, when starting from the FeIII precursor, an FeIII tosyliodinane adduct was formed and decomposed into an FeV tosylimido species which generated the catalytically active FeIV tosylimide through a comproportionation process with the FeIII precursor. [ABSTRACT FROM AUTHOR]

Although BTP (2,6-di(1,2,4-triazin-3-yl)pyridine) has been widely evidenced as the most effective nitrogen ligand for the selective complexation of trivalent actinides from lanthanide counterparts, the origin of its selectivity is still an open question. Neither experimental data nor theoretical calculations have been able to rationalize the role of covalency in real experimental BTP complexes. We show herein with DFT calculations on [M(BTP)3]3+ (M = La, U, Cm, Gd) that, even if back-bonding effects are significant in the U-BTP bond, it is the contrast of donation on 6d and 5f CmIII orbitals that explains, at least in part, its selective complexation to BTP. [ABSTRACT FROM AUTHOR]

An account of the electronic structure of AmF3 and AmCl3 has been obtained by Complete Active Space calculations (CASSCF and CASPT2) using either a scalar Douglas–Kroll–Hess Hamiltonian or a relativistic effective core potential. It has been compared to the description obtained by density functional theory (DFT) methods combined with a quasi-relativistic ZORA approach, either in the scalar or two-component approach. Optimised geometries of the ground and first excited states (7A1 and 7A2 in C3v symmetry) given by both methodologies are similar, which let us conclude that monoconfigurational DFT methods are reliable tools at least for the geometrical and bonding analysis of Am(III) complexes. [Copyright &y& Elsevier]

Multicomponent reactions are attracting strong interest because they contribute to develop more efficient synthetic chemistry. Understanding their mechanism at the molecular level is thus an important issue to optimize their operation. The development of integrated experimental and theoretical approaches has very recently emerged as most powerful to achieve this goal. In the wake of our recent investigation of amidine synthesis, we used this approach to explore how an Fe-catalyzed aziridination can lead to an imidazoline when run in acetonitrile. We report that the synthesis of imidazoline by combination of styrene, acetonitrile, an iron catalyst and a nitrene precursor occurs along a new kind of multicomponent reaction. The formation of imidazoline results from acetonitrile interception of a benzyl radical styrene aziridination intermediate within Fe coordination sphere, as opposed to classical nucleophilic opening of the aziridine by a Lewis acid. Comparison of this mechanism to that of amidine formation allows a rationalization of the modes of intermediates trapping by acetonitrile according to the oxidation state Fe active species. The molecular understanding of these processes may help to design other multicomponent reactions. [ABSTRACT FROM AUTHOR]

As part of our effort to improve our understanding of aziridination mechanism, we used tetra substitution of a diphenol ligand to modify the redox properties of corresponding Fe complexes. This allowed us to confirm that aziridination catalysis by Fe‐based complexes is governed by electron affinity of the active species and further show that it correlates with the FeIII/FeII redox potential. [ABSTRACT FROM AUTHOR]

Three D-π-A-π-A organic dyes (QX1, DTQX1 and TPZ1) were synthesized and used as photosensitizers in Dye Sensitized Solar Cells (DSSC). The molecules only vary by the nature of the linker connecting a side dithienylpyrazine motive to a triarylamine-based donating unit and a phenylcyano-acrylic acid to provide the anchoring function. By simply swapping the aromatic connecting unit the range and intensity of the absorption of the compounds can be tuned, leading to orange and green dyes. The energy levels of the frontier orbitals are well-positioned for use in DSSC with TiO 2 as the photoanode and I − /I 3 − as a redox couple in the electrolyte. Solar cells based on these sensitizers showed a power conversion efficiency (PCE) of up to 8.6% for the dyes with the narrower absorption. The lower PCE with TPZ1 is attributed to the more quinoidal nature of the π-conjugated backbone, which leads to a less favorable spatial distribution of the frontier orbitals and results in lower electron injection and higher recombination rate. [ABSTRACT FROM AUTHOR]

A mononuclear nonheme iron(V)-imido complex bearing a tetraamido macrocyclic ligand (TAML), [FeV(NTs)(TAML)]- (1), was oxidized by one-electron oxidants, affording formation of an iron(V)-imido TAML cation radical species, [FeV(NTs)(TAML+•)] (2); 2 is a diamagnetic (S = 0) complex, resulting from the antiferromagnetic coupling of the low-spin iron(V) ion (S = 1/2) with the one-electron oxidized ligand (TAML+•). 2 is a competent oxidant in C-H bond functionalization and nitrene transfer reaction, showing that the reactivity of 2 is greater than that of 1. [ABSTRACT FROM AUTHOR]

The development of iron catalysts for carbon-heteroatom bond formation, which has attracted strong interest in the context of green chemistry and nitrene transfer, has emerged as the most promising way to versatile amine synthetic processes. A diiron system was previously developed that proved efficient in catalytic sulfimidations and aziridinations thanks to an FeIIIFeIV active species. To deal with more demanding benzylic and aliphatic substrates, the catalyst was found to activate itself to a FeIIIFeIVL. active species able to catalyze aliphatic amination. Extensive DFT calculations show that this activation event drastically enhances the electron affinity of the active species to match the substrates requirements. Overall this process consists in a redox self-adaptation of the catalyst to the substrate needs. [ABSTRACT FROM AUTHOR]

The development of iron catalysts for carbon-heteroatom bond formation, which has attracted strong interest in the context of green chemistry and nitrene transfer, has emerged as the most promising way to versatile amine synthetic processes. A diiron system was previously developed that proved efficient in catalytic sulfimidations and aziridinations thanks to an FeIIIFeIV active species. To deal with more demanding benzylic and aliphatic substrates, the catalyst was found to activate itself to a FeIIIFeIVL. active species able to catalyze aliphatic amination. Extensive DFT calculations show that this activation event drastically enhances the electron affinity of the active species to match the substrates requirements. Overall this process consists in a redox self-adaptation of the catalyst to the substrate needs. [ABSTRACT FROM AUTHOR]

This article presents information on a research related to a comprehensive theoretical view of the bonding in actinide molecular complexes. The researchers based their research on model complexes of general formula F3MCO, with M = Nd, Am, and U. They also investigated I3AmCO and I3UCO to ensure the validity of their results. For this, the researchers further pointed that the already-characterized Nd and U systems were considered as references and values were compared to available experimental data. It is reported that quantum chemical topologies, such as the electronic density or electron localization function gradient field analyses which are instead based on more soundly theoretical but their interpretation may appear less straight-forward to the chemist.

We have recently reported a deprotonation-induced valence inversion within a phenoxido-bridged mixed-valent diiron(II,III) complex. The initial aniline coordinated to the FeII site reacts with triethylamine, and the resulting complex contains an anilide ligand coordinated to the FeIII ion. The behavior of these complexes in acetonitrile is indeed more intricate. Owing to the very distinctive spectroscopic signatures of the complexes, the conjunction of NMR, Mössbauer, and UV-visible absorption spectroscopies allows one to evidence two isomerization reactions, one involving the aniline linked to FeII and the other the anilide on FeIII. Theoretical calculations sustain this conclusion. Aniline in the cis position versus the bridging phenoxide is shown to be the most stable isomer while the anilide trans to the phenoxido bridge is favored. The trans isomer of the aniline complex is more acidic than the cis one by 1 pKa unit. Isomerization of the anilide complex is 10 times faster than the analogous isomerization of the aniline complex. Both reactions are proposed to proceed through a unique mechanism. This is the first time that such isomerization reactions are evidenced in dinuclear complexes. [ABSTRACT FROM AUTHOR]

Metal-catalyzed nitrene transfer reactions arouse intense interest as clean and efficient procedures for amine synthesis. Efficient Rh- and Ru-based catalysts exist but Fe alternatives are actively pursued. However, reactive iron imido species can be very short-lived and getting evidence of their occurrence in efficient nitrene-transfer reactions is an important challenge. We recently reported that a diiron(III,II) complex is a very efficient nitrene-transfer catalyst to various substrates. We describe herein how, by combining desorption electrospray ionization mass spectrometry, quantitative chemical quench experiments, and DFT calculations, we obtained conclusive evidence for the occurrence of an {FeIIIFeIVNTosyl} intermediate that is very active in H-abstraction and nitrene-transfer reactions. DFT calculations revealed a strong radical character of the tosyl nitrogen atom in very low-lying electronic configurations of the FeIV ion which are likely to confer its high reactivity. [ABSTRACT FROM AUTHOR]

Metal-catalyzed nitrene transfer reactions arouse intense interest as clean and efficient procedures for amine synthesis. Efficient Rh- and Ru-based catalysts exist but Fe alternatives are actively pursued. However, reactive iron imido species can be very short-lived and getting evidence of their occurrence in efficient nitrene-transfer reactions is an important challenge. We recently reported that a diiron(III,II) complex is a very efficient nitrene-transfer catalyst to various substrates. We describe herein how, by combining desorption electrospray ionization mass spectrometry, quantitative chemical quench experiments, and DFT calculations, we obtained conclusive evidence for the occurrence of an {FeIIIFeIVNTosyl} intermediate that is very active in H-abstraction and nitrene-transfer reactions. DFT calculations revealed a strong radical character of the tosyl nitrogen atom in very low-lying electronic configurations of the FeIV ion which are likely to confer its high reactivity. [ABSTRACT FROM AUTHOR]

A new strategy for developing dye-sensitised solar cells (DSSCs) by combining thin porous zinc tin oxide (Zn2SnO4) fiber-based photoelectrodes with purely organic sensitizers is presented. The preparation of highly porous Zn2SnO4 electrodes, which show high specific surface area up to 124 m2/g using electrospinning techniques, is reported. The synthesis of a new organic donor-conjugate-acceptor (D-π-A) structured orange organic dye with molar extinction coefficient of 44 600 M−1 cm−1 is also presented. This dye and two other reference dyes, one organic and a ruthenium complex, are employed for the fabrication of Zn2SnO4 fiber-based DSSCs. Remarkably, organic dye-sensitized DSSCs displayed significantly improved performance compared to the ruthenium complex sensitized DSSCs. The devices based on a 3 μm-thick Zn2SnO4 electrode using the new sensitizer in conjunction with a liquid electrolyte show promising photovoltaic conversion up to 3.7% under standard AM 1.5G sunlight (100 mW cm−2). This result ranks among the highest reported for devices using ternary metal oxide electrodes. [ABSTRACT FROM AUTHOR]

The article discusses a study which investigated whether single glutamate to aspartate mutation makes ferric uptake regulator (Fur) as sensitive to hydrogen peroxide as peroxide resistance regulator (PerR). It was found that the crystal structure of Bs PerR-Zn-Mn shows the coordination of the regulatory metal involves five residues arranged as a distorted square pyramid where H37, D85, H91, and D104 constitute the base of the pyramid and H93 occupies the apical position.

The article discusses research on the capability of single glutamate to aspartate mutation to develop ferric uptake regulator (Fur) as sensitive to hydrogen peroxide (H2O2 as peroxide resistance regulator (PerR). It reports that the capability of protein machinery to control metal homeostasis is one of the advances in the field of metals in biology. It also offers information on the non-involvement of PerR in metal homeostasis.

Stilbene oxide on reaction with selenocyanate ion in methanol (Culvenor et al., J Chem Soc 1949, 278) has been found to yield the corresponding stilbene with the deposition of metallic Se. For this reaction, a tentative mechanism involving 'two half rotations' around the carbon-carbon bond based on the observed stereospecificity and formation of episelenide intermediate has been suggested. This reaction has been modeled at B3LYP/6-31+G(d) level and the potential energy surface of the reaction has been explored. Computations suggest a backside attack of the selenocyanate ion to one of the epoxide carbon atoms to form a prereactive complex, two successive half-rotations around the carbon-carbon bond in the opposite direction, the formation and decomposition of episelenide intermediate, and finally trans-stilbene. Calculations besides agreeing excellently with experiment reveal many interesting mechanistic details that experimentalists could not unravel. Wiberg bond order analyses reveal the smooth progress in the bond changes during the course of the reaction. Solvent effect through PCM model calculations with methanol as solvent does not alter the gas phase results significantly. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The design of bistable magnetic systems should enable the storage of information by manipulation of the spin degrees of freedom. However, such a strategy relies on the preparation of target objects, whose environment must be controlled to favor a hysteretic behavior. Here, we report the successful modeling of a highly cooperative two-step spin-crossover iron(II) compound, [Fe(bapbpy)(NCS)2]. The magnetic susceptibility measurements and low- and high-temperature hysteretic cycles reflect the presence of an intermediate phase, which controls the memory-storage capacity of this material. It is shown that the hysteresis loop widths can be traced theoretically by evaluating the electrostatic contributions between the transiting units. Despite the apparent reduction of intermolecular interactions upon cooling, it is suggested that the enhanced fluctuations of the Madelung field are responsible for the observed hysteresis width changes. This counterintuitive scenario makes the preparation of information storage devices an even more challenging task, where theoretical inspections are very insightful. [ABSTRACT FROM AUTHOR]

Abstract: We describe a method to improve the yield and the kinetics of the difficult syntheses of α,β-unsaturated porphyrins, which enabled us to obtain a new chiral porphyrin derived from (S)-(−)-perillaldehyde in a 6% yield. Variable temperature NMR experiments on the free base, the zinc(II) and the nickel(II) complexes showed that two distinct and consecutive dynamic processes linked with the meso substituents rotation occurred. These processes can be analyzed as an evolution of the conformer composition upon temperature change. Higher values are found for the free energies of rotation of the substituent (measured by variable temperature 1H NMR) compared to those of other equivalent porphyrins like meso-tetraphenyl porphyrin or meso-tetracyclohexyl porphyrin. [Copyright &y& Elsevier]

In many theoretical studies dealing with the selective complexation of trivalent actinides with respect to trivalent lanthanides, the method of calculation is assessed by comparing computed geometries with crystal structures that are often available. Yet, the selectivity is better rationalized through thermodynamic data, as enthalpy and entropy terms. In this article, we have theoretically modeled competing complexation reactions of [Ce(terpy)3]3+, [U(terpy)3]3+, [Ce(MeBTP)3]3+ and [U(MeBTP)3]3+ systems (terpy = 2,2′:6′2″-terpyridine; MeBTP = methyl-2,6-di(1,2,4-triazin-3-yl)pyridine) within the framework of the Density Functional Theory. Our calculations manage to qualitatively account for the experimental relative stabilities of terpy and MeBTP complexes, and in particular for the better coordinating strength of MeBTP for trivalent uranium. We also show by comparing the MeBTP ligand with its non-alkylated form (HBTP) that model systems often used in quantum chemistry must be carefully chosen when energetic comparisons are undertaken. [ABSTRACT FROM AUTHOR]

Experimental uncertainties concerning the coordination mode of trivalent plutonium in concentrated LiCl have led us to theoretically evaluate the f-f transitions of a series of rare earth aquo and chloro complexes. The calculation of Pr(III), U(III), Np(III), and Pu(III) systems' spectra was undertaken using the LFDFT (ligand field density functional theory) route that combines the backgrounds of ligand field (LF) theory with Kohn-Sham orbitals. LF parameters are fitted to previous DFT calculations, thus preventing the use of empirical data. The f-f transitions values are globally well predicted, but the lack of accurate experimental references can sometimes hinder reliable comparisons. Despite this, the nephelauxetic effect from aquo to chloro complexes is clearly observed through both spectral red shifts and the decrease in F2, the Slater-Condon parameter. Accordingly, this work provides the first theoretical characterization of covalency in trivalent f elements through their electronic spectra. [ABSTRACT FROM AUTHOR]

Superoxide reductase (SOR) is an Fe protein that catalyzes the reduction of superoxide to give H2O2. Recently, the mutation of the Glu47 residue into alanine (E47A) in the active site of SOR from Desulfoarculus baarsii has allowed the stabilization of an iron-peroxo species when quickly reacted with H2O2 [Mathé et al. (2002) J. Am. Chem. Soc. 124, 4966-4967]. To further investigate this non-heme peroxo-iron species, we have carried out a Mössbauer study of the 57Fe-enriched E47A SOR from D. baarsii reacted quickly with H2O2. Considering the Mössbauer data, we conclude, in conjunction with the other spectroscopic data available and with the results of density functional calculations on related models, that this species corresponds to a high-spin side-on peroxo-Fe3+ complex. This is one of the first examples of such a species in a biological system for which Mössbauer parameters are now available: δ/Fe = 0.54 (1) mm/s, ΔEQ = -0.80 (5) mm/s, and the asymmetry parameter n = 0.60 (5) mm/s. The Mössbauer and spin Hamiltonian parameters have been evaluated on a model from the side-on peroxo complex (model 2) issued from the oxidized iron center in SOR from Pyrococcus furiosus, for which structural data are available in the literature [Yeh et al. (2000) Biochemistry 39, 2499-2508]. For comparison, similar calculations have been carried out on a model derived from 2 (model 3), where the [CH3-S]1- group has been replaced by the neutral [NH3]0 group [Neese and Solomon (1998) J. Am. Chem. Soc. 120, 12829-12848]. Both models 2 and 3 contain a formally high-spin Fe3+ ion (i.e., with empty minority spin orbitals). We found, however, a significant fraction (∼0.6 for 2, ∼0.8 for 3) of spin (equivalently charge) spread over two occupied (minority spin) orbitals. The quadrupole splitting value for 2 is found to be negative and matches quite well the experimental value. The computed quadrupole tensors are rhombic in the case of 2 and axial in the case of 3. This difference originates directly from the presence of the thiolate ligand in 2. A correlation between experimental isomer shifts for Fe3+ mononuclear complexes with computed electron densities at the iron nucleus has been built and used to evaluate the isomer shift values for 2 and 3 (0.56 and 0.63 mm/s, respectively). A significant increase of isomer shift value is found upon going from a methylthiolate to a nitrogen ligand for the Fe3+ ion, consistent with covalency effects due to the presence of the axial thiolate ligand. Considering that the isomer shift value for 3 is likely to be in the 0.61-0.65 mm/s range [Homer et al. (2002) Eur. J. Inorg. Chem., 3278-3283], the isomer shift value for a high-spin n²-O2 Fe3- complex with an axial thiolate group can be estimated to be in the 0.54-0.58 mm/s range. The occurrence of a side-on peroxo intermediate in SOR is discussed in relation to the recent data published for a side-on peroxo-Fe3+ species in another biological system [Karlsson et al. (2003) Science 299, 1039-1042]. [ABSTRACT FROM AUTHOR]

Examines the crystal structures of uranium (U) and lanthanum (La) complex. Increase of carbon-nitrogen distance in the acetonitrile derivatives; Complexation of actinides and La with tripodal aromatic amines; Structural differences between La and U complex.

The magnetic properties of the two uranium coordination compounds, [K(18c6)][U(OSi(OtBu)3)4] and [K(18c6)][U(N(SiMe3)2)4], both presenting the UIII ion in similar pseudotetrahedral coordination environments but with different O- or N-donor ligands, have been measured. The static magnetic susceptibility measurements and density functional theory studies suggest the presence of different ligand fields in the two compounds. Alternating-current susceptibility studies conducted at frequencies ranging from 95 to 9995 Hz and at temperatures in the 1.7-10 K range revealed for both compounds slow magnetic relaxation already at zero static magnetic field with similar energy barriers U ~24 K. [ABSTRACT FROM AUTHOR]

Highlights a study on the magnetic properties of various mixed-valent diruthenium long-chain carboxylates. General formula for these carboxylates; Syntheses and purification of these compounds; Reference to magnetic measurements taken; Crystal and molecular structure of one of the compounds; Interpretation of the magnetic behavior of the compounds; Conclusion drawn based on the study.