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Hexavalent neptunium can be solubilized in 0.5-3.5 M aqueous MOH (M = Li(+), Na(+), NMe4(+) = TMA(+)) solutions. Single crystals were obtained from cooling of a dilute solution of Co(NH3)6Cl3 and NpO2(2+) in 3.5 M [N(Me)4]OH to 5 °C. A single-crystal X-ray diffraction study revealed the molecular formula of [Co(NH3)6]2[NpO2(OH)4]3·H2O, isostructural with the uranium analogue. The asymmetric unit contains three distinct NpO2(OH)4(2-) ions, each with pseudooctahedral coordination geometry with trans-oxo ligands. The average Np═O and Np-OH distances were determined to be 1.80(1) and 2.24(1) Å, respectively. EXAFS data and fits at the Np L(III)-edge on solid [Co(NH3)6]2[NpO2(OH)4]3·H2O and aqueous solutions of NpO2(2+) in 2.5 and 3.5 M (TMA)OH revealed bond lengths nearly identical with those determined by X-ray diffraction but with an increase in the number of equatorial ligands with increasing (TMA)OH concentration. Raman spectra of single crystals of [Co(NH3)6]2[NpO2(OH)4]3·H2O reveal a ν1(O═Np═O) symmetric stretch at 741 cm(-1). Raman spectra of NpO2(2+) recorded in a 0.6-2.2 M LiOH solution reveal a single ν1 frequency of 769 cm(-1). Facile exchange of the neptunyl oxo ligands with the water solvent was also observed with Raman spectroscopy performed with (16)O- and (18)O-enriched water solvent. The combination of EXAFS and Raman data suggests that NpO2(OH)4(2-) is the dominant solution species under the conditions of study and that a small amount of a second species, NpO2(OH)5(3-), may also be present at higher alkalinity. Crystal data for [Co(NH3)6]2[NpO2(OH)4]3·H2O: monoclinic, space group C2/c, a = 17.344(4) Å, b = 12.177(3) Å, c = 15.273 Å, β = 120.17(2)°, Z = 4, R1 = 0.0359, wR2 = 0.0729.

The coordination of f-block cations with Schiff base oligopyrrolic macrocycles is discussed. Analysis of the mesophase of a uranyl 2,5-diformylpyrrole-derived expanded porphyrin complex through temperature-dependent X-ray diffraction (XRD) methods has provided evidence for liquid-crystalline properties, and for molecular stacking into columns, arranged in a 2D hexagonal lattice. In separate studies, UV–vis spectral analysis has indicated the formation of three new f-block oligopyrrolic complexes. Addition of neptunyl ([NpO2]2+) or plutonyl ([PuO2]2+) chloride salts to the free base of a dipyrromethane-derived Schiff base macrocycle induces an immediate spectral change, namely the growth of a Q-like band at 630 nm. Such changes in the absorption spectra cause a dramatic color change from pale yellow to blue. It is postulated that oxidation of this macrocycle, stimulated by reduction of the metal center, leads to the observed spectral changes. An immediate visible and spectral change is also observed with the reaction of lutetium silylamide (Lu[N(Si(CH3)3)2]3), with a different, tetrapyrrole-containing Schiff base macrocycle. In this case, the formation of a complex with 1:1 metal-to-ligand binding stoichiometry is further supported by MALDI-TOF mass spectrometry.

The local structure and chemical speciation of the mixed valence, fluorite-based oxides UO{sub 2+x} (0.00=

Pu L(3) X-ray absorption fine structure spectra from 24 samples of PuO(2+x) (and two related Pu-substituted oxides), prepared by a variety of methods, demonstrate that (1) although the Pu sublattice remains the ordered part of the Pu distribution, the nearest-neighbor O atoms even at x = 0 are found in a multisite distribution with Pu-O distances consistent with the stable incorporation of OH(-) (and possibly H(2)O and H(+)) into the PuO(2) lattice; (2) the excess O from oxidation is found at Pu-O distances1.9 A, consistent with the multiply bound "oxo"-type ligands found in molecular complexes of Pu(V) and Pu(VI); (3) the Pu associated with these oxo groups is most likely Pu(V), so that the excess O probably occurs as PuO(2)(+) moieties that are aperiodically distributed through the lattice; and (4) the collective interactions between these defect sites most likely cause them to cluster so as give nanoscale heterogeneity in the form of domains that may have unusual reactivity, observed as sequential oxidation by H(2)O at ambient conditions. The most accurate description of PuO(2) is therefore actually PuO(2+x-y)(OH)(2)(y).zH(2)O, with pure, ordered, homogeneous PuO(2) attained only when H(2)O is rigorously excluded and the O activity is relatively low.

The addition of aqueous pH 7 solutions of 7.2×10-3 M pertechnetate to dilute aqueous 2.5% MeOH solutions containing a water-solubilized sapphyrin, 3,12,13,22-tetraethyl-8,17-bis[bis(hydroxyethyl)-amino)carbonylethyl]-2,7,18,23-tetramethylsapphyrin (1), gives rise to spectroscopic changes in the UV–Vis spectrum of 1 that are consistent with anion-binding and sapphyrin deaggregation. The spectroscopic changes induced by pertechnetate were found to differ dramatically from those induced by the addition of either pure water or dilute nitric acid; however, they were found to parallel those seen when sodium phosphate was added to solutions of 1 under analogous experimental conditions. Fits of the spectroscopic titration data to a 1:1 binding profile revealed that the effective K describing the interaction of pertechnetate anion with 1 was ca. 3900±300 M-1; this value compares to the effective K of 23000±3000 M-1 that describes the corresponding interaction of sodium phosphate with 1.

Pu L(3) X-ray near edge absorption spectra for Pu(0-VII) are reported for more than 60 chalcogenides, chlorides, hydrates, hydroxides, nitrates, carbonates, oxy-hydroxides, and other compounds both as solids and in solution, and substituted in zirconolite, perovskite, and borosilicate glass. This large database extends the known correlations between the energy and shape of these spectra from the usual association of the XANES with valence and site symmetry to higher order chemical effects. Because of the large number of compounds of these different types, a number of novel and unexpected behaviors are observed, such as effects resulting from the medium and disorder that can be as large as those from valence.

The synthesis of a new hexapyrrolic expanded porphyrin, hexaphyrin (1.0.1.0.0.0) (1), that was found to form unique complexes of the actinide cations neptunyl (NpO2 +) and uranyl (UO2 2+) was recently reported (Sessler et al., Angew. Chem., Int. Ed. Engl. 40 (2001) 591). The present study was undertaken in an effort to generalize these findings and involves an analysis of the neptunyl (NpO2 +) and plutonyl, (PuO2 +) coordination chemistry of several other expanded porphyrin systems, including those previously reported as having formed uranyl (UO2 2+) cation complexes, in particular amethyrin ([24]hexaphyrin(1.0.0.1.0.0), 2), pentaphyrin, ([22]pentaphyrin(1.1.1.1.1), 4), and the Schiff base macrocycle, alaskaphyrin (5). This study was broadened to include the Schiff base ligand 6 (grandephyrin) and its previously unreported uranyl (UO2 2+) complex. Within moments of addition of a neptunium(VI) source to methanol solutions of the expanded porphyrins 1, 2, 4, 5 and 6, dramatic changes in the UV–Vis spectra are observed that are consistent with formation of a neptunyl complex and, in several cases, oxidation of the macrocycle. Similar changes were also observed when hexaphyrin (1), pentaphyrin (4), alaskaphyrin (5), and grandephyrin (6) were exposed to PuO2 2+. Corroborative changes are also observed in the associated 1H NMR spectra and in those portions of the electronic spectrum associated with the actinide cations. Although the formation of the proposed neptunyl and plutonyl complexes could not be substantiated by X-ray diffraction methods, the solid-state structure of the uranyl complex formed from 6 was elucidated and is presented in this report.

Treatment of nitrobenzene and other various nitroarenes with 6 equiv of samarium(II) under strictly anhydrous conditions allows for the isolation of aniline or the corresponding arylamine. Reducing the number of samarium(II) equivalents allows for the isolation of intermediate species, e.g., azoarenes or hydrazines. Use of Sm[N(SiMe3)2]2, in place of the typically used SmI2, has allowed for the detailed examination of the aqueous and nonaqueous species formed in this reduction and has been instrumental in delineation of the stepwise reaction mechanism. This is the first time that the reaction intermediates of an organic reaction mediated by samarium(II) have been isolated and analyzed by 1H NMR and X-ray crystallography.

The reaction of [Ln(OAr)3]2 with four equivalents of trialkylaluminum leads to the formation of the bis-trialkylaluminum adducts (ArO)Ln[(μ-OAr)(μ-R)AlR2]2 [Ln = La, R = Me (1); Ln = La, R = Et (3); Ln = Sm, R = Et (4)]. The X-ray crystal structure of 1 reveals short La−C(bridging) distances of 2.800(5) and 2.759(5) A. A reduced 1JC-H coupling constant of 110 Hz and a low energy ν(C−H) stretch in the solution and solid state IR spectra are consistent with a strong agostic La···H−C interaction in solution. Crystal data for 1: a = 11.708(2) A; b = 18.416(4) A; c = 20.949(4) A; α = 90°; β = 90°; γ = 90°; V = 4516.8(15) A3; Z = 4; R1 = 4.69%. The solid-state structure of the samarium ethyl derivative 4 reveals close contacts of 2.627(4) and 2.649(4) A between the samarium center and the methylene carbons of the triethylaluminum groups. The room temperature 13C NMR spectrum of 4 exhibits a 1JC-H coupling constant of 102 Hz; additionally, the fluxional process that exchanges methyl groups in 1 and 2 is slow enough on the NMR time scale to allow distinct methylene groups in 4 to be observed. Crystal data for 4: a = 19.318(1) A; b = 20.150(1) A; c = 26.280(1) A; α = 90°; β = 90°; γ = 90°; V = 10229.8(9) A3; Z = 8; R1 = 3.53%. Thermolysis of 1−4 results in ligand redistribution to form [R2Al(OAr)]2 [R = Me, Et (5)] and other unidentified species. Crystal data for 5: a = 9.496(4) A; b = 10.183(4) A; c = 18.794(7) A; α = 90.06(1)°; β = 92.394(7)°; γ = 114.976(6)°; V = 1645.6(11) A3; Z = 2; R1 = 10.13%.

Reaction of [Sm(OAr)3]2 with 4 equiv of trimethylaluminum leads to formation of the bis-trimethylaluminum adduct (ArO)Sm[(μ-OAr)(μ-Me)AlMe2]2, which exhibits very short Sm−C(bridging) distances of 2.620(5) and 2.632(5) A. A reduced 1JC-H coupling constant of 106 Hz and a low ν(C−H) stretch in the solution and solid-state IR spectrum are indicative of a strong agostic Sm···H−C interaction in solution.

Reaction of Ln[N(SiMe 3 ) 2 ] 3 (Ln=Sm, Nd) with one equivalent of the bulky heptadentate Schiff-base ligand N[CH 2 CH 2 NCH(2-OH-3,5- t -Bu 2 C 6 H 2 )] 3 ( 1 ) resulted in formation of the 7-coordinate complexes {N[CH 2 CH 2 NCH(2-O-3,5- t -Bu 2 C 6 H 2 )] 3 }Ln (Ln=Sm ( 2 ), Nd ( 3 )). X-ray diffraction studies of 2 and 3 reveal isostructural hemi-toluene solvate complexes in which the N 4 O 3 donor atom set of the ligand defines a slightly distorted capped octahedral geometry about the metal center. Ln–N bond lengths are of two types — an average of 2.556(3) A ( 2 ) (2.587(5) A ( 3 )) to the three imine nitrogens, and a significantly longer interaction of 2.818(4) A ( 2 ) (2.811(5) A ( 3 )) with the apical amine nitrogen. Ln–O distances lie in the range 2.218(3)–2.232(4) A for 2 and 2.241(6)–2.248(4) A for 3 .

Applications of actinide chemistry, whether for energy or defense purposes, have left a legacy of potential waste hazards. The new expanded porphyrin ligand 1 forms stable complexes with both uranyl (UO22+ ) and neptunyl (NpO2+ ) ions and presents a potential new avenue for waste remediation.

The tetramethylammonium counterion was used to suppress formation of insoluble uranate salts, M2U2O7, and allow for a detailed structural and spectroscopic characterization of UO2(OH)n2-n (n = 4, 5) under highly alkaline aqueous solution conditions. Single crystals of [Co(NH3)6]2[UO2(OH)4]3·H2O were obtained by cooling a dilute solution of Co(NH3)6Cl3 and UO2(NO3)2·6H2O in 3.5 M (Me4N)OH to 5 °C. The asymmetric unit contains three distinct UO2(OH)42- ions, each displaying a pseudo-octahedral coordination geometry with trans oxo ligands. The three independent UO2(OH)42- ions in the unit cell give average UO and U−OH distances of 1.82(1) and 2.26(2) A, respectively. EXAFS data on solid [Co(NH3)6]2[UO2(OH)4]3·H2O and aqueous UO22+ in 3.5 M (Me4N)OH solution were collected at the U LIII edge, and the resulting radial distribution function shows a single asymmetric peak. For the solid and solution, curve fitting reveals two near neighbors. For the crystalline solid, the first shell was fit with two O atoms at ...

The identity of the limiting Pu(IV) species under high carbonate concentrations has been determined to be Pu(CO3)56-. Single crystals of [Na6Pu(CO3)5]2·Na2CO3·33H2O were obtained from a 0.15 M solution of Pu(IV) in 2.6M Na2CO3. The asymmetric unit contains a complex network consisting of [Pu(CO3)5]6- anions and Na+ cations which are linked through interactions with CO32- and H2O ligands. Each Na+ ion is coordinated to the O atoms of H2O or CO32- ligands such that the Na+ ions achieve either octahedral or square-based pyramidal coordination. The [Pu(CO3)5]6- anion can be viewed as a pseudohexagonal bipyramid with three CO32- ligands in a equatorial plane and two in axial positions. EXAFS data for Pu(IV) in 2.5M Na2CO3 solution were collected at the Pu LIII edge. Curve fitting reveals three shells in the FT spectrum. The first shell contains ten O atoms with Pu−O = 2.42(2) A; the second shell was fit with five C atoms with Pu- - -C = 2.89(2) A; and the third shell was fit with five O atoms with Pu- - -O = 4...

Compound Cp * MoCl 2 (dppe) crystallizes in the monoclinic space group P 2 1 / c , a =16.9063(10), b =11.0118(8), c =18.6128(14) A, β =111.713(6)°, V =3219.3(4) A 3 , Z =4, D calc =1.445 Mg m −3 , μ (Mo Kα)=0.698 mm −1 , R 1=0.0448, wR 2=0.0906 for all data, R 1=0.0337, wR 2=0.0839 for 4754 data with I >2 σ ( I ). The geometry of the compound is a four-legged piano stool as typically found for this class of compounds, but the dppe ligand occupies relative trans position whereas the previously reported CpMoBr 2 (dppe) has the more common cis geometry. EPR spectroscopic investigations indicate that a mixture of isomers is present in solution and that the relative amounts of the isomers are both solvent and temperature dependent.

The first examples of stable, mononuclear 17-electron carbonyl complexes of Mo(III) have been synthesized, isolated, and characterized by IR and EPR spectroscopy. Oxidation of Cp*MoCl(CO)(PMe3)2 (1; E1/2 = −0.48 V vs Fc/Fc+), Cp*MoCl(CO)(dppe) (2; E1/2 = −0.44 V), and CpMoCl(CO)(dppe) (3; E1/2 = −0.25 V) with Fc+PF6- yields [1]PF6, [2]PF6, and [3]PF6, respectively. The IR stretching vibration of the 17-electron oxidation products are 136−153 cm-1 blue-shifted with respect to the corresponding stretching vibrations of the parent Mo(II) compounds. The room temperature EPR spectra show observable coupling to the Mo and P nuclei and indicate a trans geometry for 1+ and a cis geometry for 2+ and 3+. The four-legged piano stool geometry of 2+ with the phosphines atoms in relative cis positions has been confirmed by a single-crystal X-ray analysis. The X-ray data for [2]PF6·THF are the following: monoclinic, P21/n, a = 13.7394(14) A, b = 20.421(2) A, c = 14.857(2) A, β = 99.119(8)°, V = 4115.8(8) A3, Z = 4, Dx ...

Several phosphine exchange processes on 17-electron CpMoCl2(PR3)2 systems have been investigated. The exchange of two PPh3 ligands with either two PMe3 ligands or with Ph2PCH2PPh2 (dppe) is complete within a few minutes at −80 °C. Equally fast is the exchange of two PEt3 ligands with two PMe3 ligands. On the other hand, the exchange of two PEt3 ligands with dppe is much slower (t12 ≈ 15 min to a few hours at r.t.), with excess dppe accelerating the exchange and free PEt3 retarding it. The self-exchange reaction of PMe3 is extremely slow (less than 25% exchange at r.t. in 6 h at r.t.) and an analysis of the initial rate of this reaction shows a two-term rate law with one [PMe3]-dependent and one independent term. Finally, PMe3 self-exchange on Cp∗MoCl2(PMe3)2 proceeds over one order of magnitude faster than for the corresponding Cp system, with a substantially [PMe3]-independent rate law. All these data are indicative of a dominant dissociative exchange mechanism involving rupture of the MoPR3 bond in the slow step and formation of a 15-electron intermediate. The rate of phosphine dissociation qualitatively correlates with the MoP distance in the 17-electron starting complex. Only for the CpMoCl2(PMe3)2 system is phosphine dissociation sufficiently slowed down so that the alternative associative exchange pathway becomes competitive. Possible reasons for a low activation barrier in these dissociative exchanges are discussed.

The complex Cp★MoCl2(PMe2Ph)2 (Cp★ = η5C5Me5) has been obtained in good yield from Cp☆MoCl4, PMe2Ph2, and Na in the appropriate stoichiometric ratio, and it is also obtained by a ligand redistribution process after reduction of Cp☆MoCl3- (PMe2Ph) with Na. This compound is oxidized by the CH2Cl2 solvent in the presence of AlCl3 to afford the salt [Cp☆MoCl2(PMe2Ph)2AlCl4. Both compounds have been characterized crystallographically and by 1H-NMR spectroscopy. The reasons for the instability of 15-electron Cp☆MoCl2L complexes are discussed. The 1H-NMR resonance data for Cp ☆ MoCl 2 L 2 ( L = PMe 3 , PMe 2 Ph ) and [Cp☆MoCl2(PMe2Ph)2]+ are also discussed.

The Inorganic and Coordination Chemistry of the 5f elements (Actinides) is intermediate between that of the transition metals and the 4f elements (Lanthanides). The first four members of the actinide series, Ac, Th, Pa, and U, are all naturally occurring but have unstable nuclei, making them radioactive. The other elements in the actinide series (transuranium elements or transuranics) are also radioactive and have been made by man through a variety of nuclear transformation processes, for example, neutron irradiation, atom bombardment, and radioactive decay. The actinide series may be broken into two separate groups, the light or early actinides (Ac–Am) and the heavy or late actinides (Cm–Lr). The chemical behaviors of these two groups are distinct. The light actinides are capable of being stabilized in a variety of oxidation states, for example, II to VII, and have been found to exhibit a significant degree of covalency in binding ligands. The heavy actinides are more reminiscent of the lanthanides in that the most persistent oxidation state is the trivalent and the bonding predominately occurs through ionic interactions. This difference has led to a substantial number of studies into the role of the 5f orbitals in structure and bonding of the actinides. One of the ions that has received a great deal of attention is the ubiquitous actinyl ion, AnO22+/+. This ion is the stable form for all aqueous complexes of the pentavalent and hexavalent light actinides. The oxo ligands are always found in a trans geometry and are strongly bound (triple bond) through a combination of σ- and π-bonds with the 5f and 6d orbitals of the actinide metal center. While these strong covalent interactions exist with the axial oxo ligands, the bonding within the equatorial plane is primarily based on ionic interactions. The ability of the light actinides to access multiple oxidation states leads to rich and, sometimes, complex electrochemistry. For example, under acidic conditions the reduction potentials for PuO22+, PuO2+, Pu4+, and Pu3+ are all close to 1 V. The physical manifestation of these close reduction potentials is an aqueous solution in which the plutonium can exist in four different oxidation states simultaneously. By careful control of the conditions, oxidation state pure solutions can be obtained for quantitative and qualitative studies. The binding affinities of the actinide ions to ligands follow the general trend An4+ > An3+ ∼ AnO22+ ≫ AnO2+. Since the actinides are strong acids, the ions preferentially bond strong bases, for example, halides, oxygen donors, and so on. Owing to the greater degree of covalency in actinide complexes compared to the lanthanides, complexes with ligands having nitrogen, phosphorus, sulfur, and selenium donors are also found. Keywords: actinides; f elements; transuranics; radioactivity; coordination chemistry; actinide contraction; relativistic effects; nuclear fuel

The first single-crystal X-ray diffraction study of a lanthanide tricarbonate complex, namely [Co(NH3)6][Sm(CO3)3(H2O)]·4H2O, is reported and reveals a zigzag chain structure of 9-coordinate samarium metal centers bridged by μ-η2∶η1 carbonate ligands.

Experimental L(III) X-ray absorption near edge structure (XANES) spectra of the distorted octahedral neptunium oxo ions NpO(2)(OH)(4)(2-), NpO(4)(OH)(2)(3-), and NpO(6)(6-) are interpreted using relativistic full multiple scattering calculations of the X-ray absorption process. In this series of compounds, the neptunium cation exhibits two different oxidation states, VI and VII, with coordination spheres from di- to tetra oxo for the first two compounds. The comparison between calculated XANES spectra using the feff code and experimental ones shows that the main features in the spectra are determined by the local coordination around the actinide metal center. Furthermore, the projected density of electronic states (DOS) calculated from the XANES simulations using the feff code are compared to calculations using ADF code. They are both discussed in terms of molecular orbitals and qualitative evolution of bonding within this series of compounds.

An overview is provided on thorium and thorium compounds with an emphasis on their relevance to chemical technology. The main interest in thorium is as a nuclear fuel, but thorium and its compounds have many specialty uses including lantern mantles and catalysts. Discussion on the occurrence, recovery, preparation, properties and radiochemistry of thorium is provided. While not intending to be exhaustive, a broad based review is provided on the coordination and organometallic complexes of thorium with halogens; N, P, and O donors; cyclopentadienyl; annulene; hydrocarbyl; and allyl ligands. A drawback to using thorium in many processes is the chemical reactivity of the metal as well as the inherent radioactivity of all thorium isotopes. As such, health and safety factors essential for working with thorium are discussed. General references from which more detailed information of the aforementioned subjects is provided. Keywords: thorium; thorium compounds; actinides; radioactivity; occurrence; recovery; ores; metal; lantern mantles; refractory materials; coordination complexes; organometallic compounds; oxo ion salts; nuclear fuel

Pu L 3 XAFS measurements show that the excess oxygen in single phase PuO 2 + x occurs as oxo groups with Pu-O distances of 1.83-1.91 A. This distance and the energy of the edge (via comparison with a large number of related compounds) are more consistent with a Pu(IV/V) than a Pu(IV/VI) mixture. Analogous to Pu(IV) colloids, although the Pu-Pu pair distribution remains single site even when it shows substantial disorder, the Pu-O distribution can display a number of additional shells at specific distances up to 3.4 A even in high fired materials when no oxo groups are present, implying intrinsic H + /OH - (/H 2 O). The number of oxo atoms increases when samples are equilibrated with humid air at ambient temperature, indicating that the Pu reactivity in this solid system differs notably from that of isolated complexes and demonstrating the importance of nanoscale cooperative phenomena and total free energy in determining its chemical properties.

A new methodology for the preparation of alpha-diimines and beta-aminoenones has been devised and represents an alternative route to these and related nitrogenous ligands bearing highly electronegative substituents.

The compound Sm[N(SiMe(3))(2)](3) has been investigated experimentally by X-ray crystallography and computationally by DFT methods. The structure is analogous to that of other tris[bis(trimethylsilyl)amido]lanthanides, featuring positional disorder of the metal atom above and below the plane defined by the three N donor atoms, resulting in a trigonal pyramidal configuration. One of the methyl groups of each amido ligand is placed above the apex of the pyramid at close distance to the metal center suggesting the presence of agostic interactions. The DFT calculations have been carried out on the real molecule and on a Si[N(SiH(3))(SiH(2)Me)](3) model where the unique Me group was placed above the apex of the pyramid to probe the agostic interaction. In both cases, the optimized geometry reproduces very well the experimental structure and indicates the presence of beta-Si-C agostic interactions. A comparison of the optimized geometries obtained in the presence/absence of the Sm d and the Si d orbitals serves to illustrate the relevance of these orbitals for (i). the establishment of the pyramidal configuration at Sm, (ii). the Sm-N bond length, and (iii). the Sm-(beta-Si-C) bond length. The bonding analysis, which was carried out by both Mulliken and NBO methods, not only confirms the importance of the metal d orbitals for the Sm-N and Sm-(beta-Si-C) chemical bonding but also illustrates the relevance of electrostatic terms in the agostic interaction. Sm-N and N-Si pi bonding is present according to the bonding analysis but is not important for enforcing the planar configuration at N, nor the pyramidal configuration at Sm.

Treatment of nitrobenzene and other various nitroarenes with 6 equiv of samarium(II) under strictly anhydrous conditions allows for the isolation of aniline or the corresponding arylamine. Reducing the number of samarium(II) equivalents allows for the isolation of intermediate species, e.g., azoarenes or hydrazines. Use of Sm[N(SiMe(3))(2)](2), in place of the typically used SmI(2), has allowed for the detailed examination of the aqueous and nonaqueous species formed in this reduction and has been instrumental in delineation of the stepwise reaction mechanism. This is the first time that the reaction intermediates of an organic reaction mediated by samarium(II) have been isolated and analyzed by (1)H NMR and X-ray crystallography.

An overview of uranium and uranium compounds with an emphasis on their relevance to chemical technology is provided. Uranium and its compounds have many uses both potential and applied; examples include nuclear fuel, radiation shielding, and kinetic energy penetrators. These uses have a substantial economic impact, the aspects of which are provided. Sections are provided that illustrate the occurrence, recovery, and radiochemistry of uranium as well as the properties and preparation of uranium metal. A broad overview of uranium coordination and organometallic compounds is also provided. Drawbacks to the application of uranium and uranium compounds in many processes include the chemical reactivity of the metal and the inherent radioactivity of uranium isotopes. As such, health and safety factors that must be taken into account while working with uranium are discussed. Keywords: uranium; uranium compounds; uranium alloys; isotope enrichment; safety; nuclear fuel; radiation shielding; organometallic compounds; recovery; sandwich type compounds; radiochemistry

Applications of actinide chemistry, whether for energy or defense purposes, have left a legacy of potential waste hazards. The new expanded porphyrin ligand 1 forms stable complexes with both uranyl (UO

By utilizing X-ray absorption methods, e.g., extended x-ray absorption fine structure (EXAFS) and single crystal x-ray diffraction (XRD), as well as Raman, UV-Vis and fluorescence spectroscopy, we have shown that an equilibrium exists between the monomeric uranyl hydroxide species UO2(OH)42− and UO2(OH)53−, which is dependent upon hydroxide concentration. Upon further study of this system, we have now determined that a new hydrolysis product is present in equilibrium with the monomeric uranyl hydroxide species, which is favored at higher UO22+ concentrations.

International audience; The first comparative kinetic study of the addition of the isolobal and isosteric CO and N2 ligands to a spin triplet organometallic compound, i.e. Cp*MoCl(PMe3)2, is reported. A fast and quantitative addition process occurred when interacting Cp*MoCl(PMe3)2 with CO, which is followed by a subsequent slower process involving PMe3 replacement and formation of Cp*MoCl(CO)2(PMe3). The N2 addition, on the other hand, is much slower and proceeds incompletely to an equilibrium position. The temperature dependence of this equilibrium gives the parameters for the reaction ΔH = −22.8 ± 2.1 kcal/mol and ΔS = −67 ± 7 cal·mol-1·K-1. The activation parameters for the CO addition are ΔH⧧ = 5.0 ± 0.3 kcal/mol and ΔS⧧ = −35 ± 4 cal·mol-1·K-1, while the activation parameters for the N2 addition are ΔH⧧ = 14.0 ± 1.0 kcal/mol and ΔS⧧ = −20 ± 3 kcal/mol. Extrapolation of the rates to 25 °C indicates a difference of more than three orders of magnitude: kCO = 29 ± 3 M-1 s-1 and kN2 = 0.014 ± 0.001 M-1 s-1. Theoretical calculations with full geometry optimization at the MP2 level have been carried out on the model systems CpMoCl(PH3)2 + L (L = CO or N2), the calculated energetics of the system being in agreement with experiment. The 16-electron CpMoCl(PH3)2 molecule is found to be more stable in the spin triplet state, the excited 1A‘ state being 10.9 kcal/mol higher in energy. The Mo−L bond formation is calculated to be exothermic by 27.9 kcal/mol for L = N2 and by 60.0 kcal/mol for L = CO. Calculations along the L addition coordinate show an initial ligand rearrangement related barrier for both the spin singlet and the spin triplet surfaces. After overcoming this barrier, the spin singlet curve descends in energy earlier for the CO vs the N2 addition as expected from greater diffuseness of the CO donor and acceptor orbitals. As the N2 ligand continues to approach the metal, the 3A‘‘ surface becomes increasingly repulsive whereas the addition of CO leads to an attractive interaction and a bound triplet state.

The controlled sodium reduction of Nb(cp)Cl 4 L (cp = η-C 5 H 5 ; L = PMe 3 , PMe 2 Ph or PMePh 2 ) or Nb(η-C 5 Me 5 )Cl 4 in the presence of PMe 3 afforded the mononuclear 15-electron complexes Nb(cp)Cl 3 L and Nb(η-C 5 Me 5 )Cl 3 (PMe 3 ), respectively. Reduction of Nb(cp)Cl 4 in the presence of an excess of L for PMe 2 Ph and PMePh 2 afforded solids that contain mainly the 17-electron Nb(cp)Cl 3 L 2 species but are contaminated by the mono-L derivatives. A UV/VIS investigation of the solution equilibrium between Nb(cp)Cl 3 (PMe 2 Ph) 2 and Nb(cp)Cl 3 (PMe 2 Ph) plus free PMe 2 Ph afforded an enthalpy of 19.0 ± 1.6 kcal mol -1 and an entropy of 45 ± 5 cal K -1 mol -1 for the ligand dissociation process. A comparative study of the equilibrium between Mo(cp)Cl 3 (PMe 2 Ph) 2 and Mo(cp)Cl 3 (PMe 2 Ph) plus free PMe 2 Ph cannot be carried out because the equilibration is too slow at room temperature and because of thermal decomposition with ring loss at high temperature. Theoretical calculations at the second-order Moller-Plesset perturbation (MP2) level on the M(cp)Cl 3 (PH 3 ) n (M = Nb or Mo, n = 1 or 2) model systems afforded geometries in good agreement with experimental examples. The calculated PH 3 dissociation energy for M = Nb of 21.3 kcal mol -1 is in good agreement with experiment. For M = Mo, the more saturated complex is stabilized by 32.8 kcal mol -1 relative to the excited 1 A′ state and by 23.5 kcal mol -1 relative to the ground 3 A″ state. Therefore, the regain of pairing energy upon PH 3 dissociation from Mo(cp)Cl 3 (PH 3 ) 2 provides a calculated stabilization for the 16-electron monophosphine complex of 9.3 kcal mol -1 . The observed variations of bonding parameters upon metal change from Nb to Mo and a natural population analysis suggest that the main reason for a greater Mo–PH 3 bonding interaction is the greater extent of both M–P σ bonding and π back bonding for the d 2 metal relative to the d 1 metal.

International audience; The structure and the energetics of the model systems CpMX2(PH3) + PH3 ⇄ CpMX2(PH3)2 (Cp = cyclopentadienyl; M = Cr, Mo; X = Cl, CH3) are studied by performing Møller−Plesset second order (MP2) and density functional theory (DFT) calculations. Extended basis sets are employed in the geometry optimizations. The results indicate that the structural preference can be traced back to the competition between electron pairing stabilization and M−P bond dissociation energy along the spin doublet surface. At all levels of calculation, the energy splitting, a measure of the cost of pairing the electron during the promotion process from the quartet ground state to the excited doublet state for CpCrX2(PH3), is found to be on average 15−20 kcal/mol greater than the energy gain associated with the formation of the new Cr−PH3 bond along the spin doublet surface. For the analogous Mo chloride system the reverse appears to be true, the products with higher coordination being energetically favored by 10−12 kcal/mol. These data are in agreement with experimental evidence.

International audience; Sodium reduction of (ring)NbCl4 in the presence of the appropriate phosphine ligand affords the 16-electron Nb(III) complexes (ring)NbCl2L2 (ring = C5H5, L2 = dppe or ring = C5H4Me, L = PEt3). While the previously reported Cp*NbCl2(PMe3)2 complex behaves as a Curie−Weiss spin triplet paramagnet, compound (C5H4Me)NbCl2(PEt3)2 has a spin singlet ground state and a thermally populated excited triplet state (2.3 kcal/mol higher in energy) and (C5H5)NbCl2(dppe) is essentially diamagnetic. The X-ray structure of (C5H4Me)NbCl2(PEt3)2 shows a four-legged piano stool geometry, with Cl−Nb−Cl and P−Nb−P angles correlating with the experimentally determined singlet ground state. Theoretical calculations with geometry optimization at the MP2 level on both 1A‘ and 3A‘‘ states for the (C5H5)NbCl2(PH3)2 model system confirm the strong dependence of the angular parameters on the spin state.

International audience; Monocyclopentadienyl complexes of Mo(II) with 16- and 18-electron configurations of the form (Ring)MoClLx (x = 2, Ring = Cp, L = PMe2Ph; x = 2, Ring = Cp*, L = PMe3, PMe2Ph, L2 = dppe; x = 3, Ring = Cp, L = PMe2Ph) are described. All of the 16-electron complexes are paramagnetic with an S = 1 ground state, as shown by magnetic measurements in the solid state and in solution, and by the contact-shifted 1H NMR spectra. The structure of Cp*MoCl(dppe) was determined by X-ray diffraction methods. The 18-electron complex CpMoCl(PMe2Ph)3 has been synthesized by reduction of {CpMoCl2}n with Na in the presence of 3 equiv of phosphine. It has been fully characterized by 1H and 31P NMR, chemical analysis, and X-ray structural determination. Thermolysis of a THF or C6D6 solution of this 18-electron species generates the 16-electron paramagnetic Mo(II) complex CpMoCl(PMe2Ph)2. The Cp*MoClL2 (L = PMe3 and PMe2Ph) systems react with 2-electron-donor ligands, i.e. CO and H2, to afford stable 18-electron complexes. The carbonyl derivative Cp*MoCl(CO)(PMe2Ph)2 has also been characterized by X-ray crystallography.

The identity of the limiting HoIII species in aqueous solutions with high carbonate concentrations has been determined to be Ho(CO3)45−. Single crystals of [Co(NH3)6][Na(μ−H2O)(H2O)4]2[Ho(CO3)4]·4H2O were obtained by the addition of [Co(NH3)6]3+ to an aqueous 0.04 M solution of HoIII in 2.1 M Na2CO3. The asymmetric unit contains the anion, [Ho(CO3)4]5−, a [Co(NH3)6]3+ cation and two Na+ cations, which are bound to H2O molecules in an edge-sharing bioctahedral geometry. The [Ho(CO3)4]5− anion is eight coordinate with four bidentate carbonate ligands bound to the Ho atom. The molecule has essentially C2v symmetry with two coplanar carbonates making a vane, which is perpendicular to a similar vane produced by the other two carbonate ligands. An alternative way to this view molecule is through the geometry of the C atoms, which are found in a distorted tetrahedron. The average Ho−O distance was determined to be 2.361(5) A, while the average Ho−C distance was 2.784(6) A. The IR and Raman spectra were determined in both the solid state and solution in order to confirm the solution speciation. The Raman data show a single CO32− stretch for the solid at 1062 cm−1. The solution data show multiple peaks with the most prominent being at 1048 cm−1, which is consistent with the literature reports of an equilibrium mixture. The IR data for the solids confirm the X-ray results showing bidentate carbonate ligands by the splitting of the ν3 band of the CO32−. The crystal data for [Co(NH3)6][Na(μ-H2O)(H2O)4]2[Ho(CO3)4]·4H2O are as follows: monoclinic space group P2/n, a = 8.7091(5) A, b = 10.8744(6) A, c = 15.7971(9) A, β = 93.117(1)°, Z = 2, R1 = 0.0307, wR2 = 0.0756.

Complexes [C5Me5MoClL2](L = tertiary phosphine) are rare examples of stable cyclopentadienylmolybdenum(II) 16-electron complexes and the first such complexes with a spin triplet ground state.