D. Webster Keogh

Hexaphyrin(1.0.1.0.0.0): An Expanded Porphyrin Ligand for the Actinide Cations Uranyl (UO22+) and Neptunyl (NpO2+)

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.

Monoprotonated Sapphyrin–Pertechnetate Anion Interactions in Aqueous Media

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.

Chemical Speciation of Neptunium(VI) under Strongly Alkaline Conditions. Structure, Composition, and Oxo Ligand Exchange

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.

A Model for Trivalent Actinides in Media Containing High Carbonate Concentrations − Structural Characterization of the Lanthanide Tetracarbonate [Co(NH3)6][Na(μ-H2O)(H2O)4]2[Ho(CO3)4]·4H2O

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.

Synthese und Struktur des ersten Transuran‐Kronenether‐Einschlußkomplexes: [NpO2([18]krone‐6)][ClO4]

Eindeutig in der ersten Koordinationssphare des Dioxoactinoid-Ions befindet sich der Kronenetherligand im Komplex-Ion [NpO2([18]krone-6)]+ 1. Dieses entsteht relativ leicht durch Zugabe von [18]Krone-6 zu einer wasrigen Losung von NpO2+ oder NpO22+ in verdunnter HClO4 oder CF3SO3H. Rontgenstrukturanalyse und spektroskopische Daten von 1[ClO4] belegen die Komplexstruktur zweifelsfrei.

First single-crystal X-ray diffraction study of a lanthanide tricarbonate complex: [Co(NH3)6][Sm(CO3)3(H2O)]·4H2O

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 and theoretical comparison betweenM(cp)Cl3Ln systems of NbIV andMoIV(cp = η-C5H5)

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.

Dialkyl aluminium amides: new reagents for the conversion of C???O into C???NR functionalitiesElectronic supplementary information (ESI) available: HRMS, 1H and 19F NMR data for 1???9. See http://www.rsc.org/suppdata/cc/b2/b203693b/

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.

Identification of oligomeric uranyl complexes under highly alkaline conditions

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.