Daniel Lundberg

Hydration and Hydrolysis of Thorium(IV) in Aqueous Solution and the Structures of Two Crystalline Thorium(IV) Hydrates

Solid octaaqua(kappa(2)O-perchlorato)thorium(IV) perchlorate hydrate, [Th(H(2)O)(8)(ClO(4))](ClO(4))(3).H(2)O, 1, and aquaoxonium hexaaquatris(kappaO-trifluoromethanesulfonato)thorium(IV) trisaquahexakis(kappaO-trifluoromethanesulfonato)thorinate(IV), H(5)O(2)[Th(H(2)O)(6)(OSO(2)CF(3))(3)][Th(H(2)O)(3)(OSO(2)CF(3))(6)], 2, were crystallized from concentrated perchloric and trifluoromethanesulfonic acid solutions, respectively. 1 adopts a severely distorted tricapped trigonal prismatic configuration with an additional oxygen from the perchlorate ion at a longer distance. 2 consists of individual hexaaquatris(kappaO-trifluoromethanesulfonato)thorium(IV) and trisaquahexakis(kappaO-trifluoromethanesulfonato)thorinate(IV) ions and an aquaoxonium ion bridging these two ions through hydrogen bonding. The hydrated thorium(IV) ion is nine-coordinated in aqueous solution as determined by extended X-ray absorption fine structure (EXAFS) and large angle X-ray scattering (LAXS). The LAXS studies also showed a second hydration sphere of about 18 water molecules, and traces of a 3rd hydration sphere. Structural studies in aqueous solution of the hydrolysis products of thorium(IV) have identified three different types of hydrolysis species: a mu(2)O-hydroxo dimer, [Th(2)(OH)(2)(H(2)O)(12)](6+), a mu(2)O-hydroxo tetramer, [Th(4)(OH)(8)(H(2)O)(16)](8+), and a mu(3)O-oxo hexamer, [Th(6)O(8)(H(2)O)(n)](8+). Detailed structures of these three hydrolysis species are given. A compilation of reported solid state structures of actinoid(IV) compounds with oxygen donor ligands show a strong correlation between the An-O bond distance and the coordination number. The earlier reported U-O bond distance in the hydrated uranium(IV) ion in aqueous solution, confirmed in this study, is related to nine-coordination. The hydrated tri- and tetravalent actinoid ions in aqueous solution all seem to be nine-coordinated. The trivalent ions show a significant difference in bond distance to prismatic and capping water molecules in assumed tricapped trigonal prismatic configuration, while the tetravalent ions seem to form more regular structures, probably because of higher polarization.

Thallium(I) complexes with modified poly(pyrazolyl)borate ligands—metal-ligand coordination and crystal packing

Abstract The structures of the thallium(I) complexes with hydrotris(pyrazolyl)borate (TpTl, 2-Tl), and the modified Bp and Tp ligands dihydrobis(1,2,4-triazolyl)borate (3-Tl), hydrotris(imidazolyl)borate (6-Tl), dihydrobis(indazolyl)borate (7-Tl), and hydrotris(indazolyl)borate (8-Tl) are reported and discussed in terms of their (molecular) metal–ligand arrangement and their crystal packing. Compounds 2-Tl and 7-Tl feature molecular TpTl and Bp′Tl units with pronounced Tl⋯πazolyl interactions between neighboring molecules. In 8-Tl the molecular units are arranged in pairs through indazolyl π⋯π stacking. Complexes 3-Tl and 6-Tl form extended 3D and 1D structures, respectively, through the bridging action of the poly(azolyl)borate ligand between three symmetry related thallium centers. Compounds 2-Tl, 3-Tl, and 8-Tl crystallize in the chiral space groups P21, P212121, and C2, respectively.

Structural and Electronic Snapshots during the Transition from a Cu(II) to Cu(I) Metal Center of a Lytic Polysaccharide Monooxygenase by X-ray Photoreduction

Background: Lytic polysaccharide monooxygenases (LPMOs) exhibit a copper center that binds dioxygen for catalysis. Results: We present LPMO structures from Cu(II) to Cu(I) and analyze the transition with quantum mechanical calculations. Conclusion: Reduction changes the copper coordination state but requires only minor structural and electronic changes. Significance: These structures provide insight into LPMO catalytic activation for further mechanistic studies. Lytic polysaccharide monooxygenases (LPMOs) are a recently discovered class of enzymes that employ a copper-mediated, oxidative mechanism to cleave glycosidic bonds. The LPMO catalytic mechanism likely requires that molecular oxygen first binds to Cu(I), but the oxidation state in many reported LPMO structures is ambiguous, and the changes in the LPMO active site required to accommodate both oxidation states of copper have not been fully elucidated. Here, a diffraction data collection strategy minimizing the deposited x-ray dose was used to solve the crystal structure of a chitin-specific LPMO from Enterococcus faecalis (EfaCBM33A) in the Cu(II)-bound form. Subsequently, the crystalline protein was photoreduced in the x-ray beam, which revealed structural changes associated with the conversion from the initial Cu(II)-oxidized form with two coordinated water molecules, which adopts a trigonal bipyramidal geometry, to a reduced Cu(I) form in a T-shaped geometry with no coordinated water molecules. A comprehensive survey of Cu(II) and Cu(I) structures in the Cambridge Structural Database unambiguously shows that the geometries observed in the least and most reduced structures reflect binding of Cu(II) and Cu(I), respectively. Quantum mechanical calculations of the oxidized and reduced active sites reveal little change in the electronic structure of the active site measured by the active site partial charges. Together with a previous theoretical investigation of a fungal LPMO, this suggests significant functional plasticity in LPMO active sites. Overall, this study provides molecular snapshots along the reduction process to activate the LPMO catalytic machinery and provides a general method for solving LPMO structures in both copper oxidation states.

Characterization of phosphate sequestration by a lanthanum modified bentonite clay: a solid-state NMR, EXAFS, and PXRD study.

Phosphate (Pi) sequestration by a lanthanum (La) exchanged clay mineral (La-Bentonite), which is extensively used in chemical lake restoration, was investigated on the molecular level using a combination of (31)P and (139)La solid state NMR spectroscopy (SSNMR), extended X-ray absorption spectroscopy (EXAFS), powder X-ray diffraction (PXRD) and sorption studies. (31)P SSNMR show that all Pi was immobilized as rhabdophane (LaPO4·n H2O, n ≤ 3), which was further supported by (139)La SSNMR and EXAFS. However, PXRD results were ambiguous with respect to rhabdophane and monazite (LaPO4). Adsorption studies showed that at dissolved organic carbon (DOC) concentration above ca. 250 μM the binding capacity was only 50% of the theoretical value or even less. No other La or Pi phases were detected by SSNMR and EXAFS indicating the effect of DOC is kinetic. Moreover, (31)P SSNMR showed that rhabdophane formed upon Pi sequestration is in close proximity to the clay matrix.

Heavy metal removal from aqueous solutions by sorption using natural clays from Burkina Faso

The acid-base properties of two raw and purified mixed clays from Burkina Faso were studied, as well as their potential to remove copper(II), lead(II) and chromium(III), and thereby their ability to be used to purify water from heavy metals. The purification procedure of the clays involved removal of carbonates, iron oxides and organic matter. A determination of the elemental composition of the mixed clays revealed the presence of aluminum, iron and silicon as main constituents. The high alkaline pH in one of the samples is attributable to the presence of carbonate in the raw clay. The point of zero charge (pH pzc ) values of the clays, as determined by potentiometric titrations, were 6.79 and 9.52 for the raw clays, while after purification they were 6.87 and 6.76, respectively. Metal adsorption to the clay surfaces started at pH values below pH pzc , strongly indicating formation of inner-sphere complexes. With contact time of 48 h, complete removal of copper(II) was achieved at pH 8 for all samples. More than 90% of the lead(II) removal was attributed to adsorption while for chromium(III), it was 85%. Adsorption to organic matter and iron oxides, and precipitation of metal hydroxides gave significant contributions to the removal of metal ions in aqueous systems. Key words: Mixed clays, potentiometric titration, heavy metals, pH pzc .

Surface behavior of amphiphiles in aqueous solution: a comparison between different pentanol isomers

Position isomerism is ubiquitous in atmospheric oxidation reactions. Therefore, we have compared surface-active oxygenated amphiphilic isomers (1- and 3-pentanol) at the aqueous surface with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. The experimental data are complemented with molecular dynamics (MD) simulations. A concentration-dependent orientation and solvation of the amphiphiles at the aqueous surface is observed. At bulk concentrations as low as around 100 mM, a monolayer starts to form for both isomers, with the hydroxyl groups pointing towards the bulk water and the alkyl chains pointing towards the vacuum. The monolayer (ML) packing density of 3-pentanol is approx. 70% of the one observed for 1-pentanol, with a molar surface concentration that is approx. 90 times higher than the bulk concentration for both molecules. The molecular area at ML coverage (≈100 mM) was calculated to be around 32 ± 2 Å(2) per molecule for 1-pentanol and around 46 ± 2 Å(2) per molecule for 3-pentanol, which results in a higher surface concentration (molecules per cm(2)) for the linear isomer. In general we conclude therefore that isomers - with comparable surface activities - that have smaller molecular areas will be more abundant at the interface in comparison to isomers with larger molecular areas, which might be of crucial importance for the understanding of key properties of aerosols, such as evaporation and uptake capabilities as well as their reactivity.

On the Structure and Volumetric Properties of Solvated Lanthanoid(III) Ions in Amide Solutions

The coordination chemistry and the volumetric properties of three representative lanthanoid(III) ions--lanthanum(III), gadolinium(III), and lutetium(III)--have been studied in three amide solvents with gradually increasing spatial demand upon coordination: N,N-dimethylformamide (dmf) < N,N-dimethylacetamide (dma) < N,N-dimethylpropionamide (dmp). Large angle X-ray scattering (LAXS) and EXAFS have been used to determine the structure of the solvated lanthanoid(III) ions in solution, further supplemented with a crystallographic study on octakis(N,N-dimethylacetamide)lanthanum(III) triflate, [La(dma)8](CF3SO3)3. The selection of ions and solvents allows an estimate of the steric congestion effects on the resulting coordination number, CN, ranging from nine for lanthanum(III) ions in dmf to seven for the smaller lutetium(III) ion in space-demanding dma. The standard partial molar volumes of the solvated lanthanoid(III) ions in water and dmf are reflected in the CNs, as these solvent molecules are small enough to not interfere with each other upon coordination. However, the larger and more space-demanding dma displays a different pattern with an almost constant standard partial molar volume and a decreasing CN, counterbalancing the difference in ionic radius of the lanthanoid(III) ion.

The furan­osteroid viridiol

The asymmetric unit of the title compound, C20H18O6 (systematic name: 1β,3β-dihydroxy-2β-methoxyfuro[4′,3′,2′:4,5,6]-18-norandrosta-8,11,13-triene-7,17-dione), a dihydro derivative of the fungal steroid viridin, contains two molecules with similar conformations. The rings bearing the hydroxy groups adopt boat conformations. The absolute structure was assigned based on the known chirality of a precursor compound. In the crystal, molecules are linked by O—H⋯O hydrogen bonds, generating a three-dimensional network and weak C—H⋯O interactions consolidate the packing.

On the coordination chemistry of the dimercury(I) ion with O-donor ligands

Abstract An overview of published crystalline dimercury(I) hydrates, solvates, and complexes/compounds with O-donor ligands shows that there is virtually no correlation between the Hg—Hg bond distance and the overall Hg—O bonding conditions. Additionally, many structures feature different configurations for the individual mercury atoms in the dimercury(I) ion, Hg22+. To supplement these findings, the crystal structures of the perchlorate salts of hydrated and dimethylsulfoxide (dmso) solvated mercury(I), [Hg2(OH2)2](ClO4)2 (1) and [Hg10(OS(CH3)2)16](ClO4)10 (2), respectively, have been determined by single crystal X-ray diffraction. In compound 1, the perchlorate ions act as bridges between the almost linear [Hg2(OH2)2]2+ units forming infinite chains. The Hg—Hg bond distance is 2.500(1) Å and the Hg—O distance to the water molecule is 2.231(19) Å. Additional much weaker Hg—O bonds to the bridging perchlorate oxygens lie in the range 2.78–3.15 Å. Compound 2 consists of five crystallographically independent [Hg—Hg]2+ units solvated and bridged by dmso oxygens. These larger entities form chains through much weaker bridging perchlorate ions at longer distances, 3.0–3.3 Å, with a few remaining perchlorate ions isolated in the lattice. The mean Hg—Hg bond distance is 2.500(1) Å, while the Hg—Odmso bond distances are in the range of 2.15–2.92 Å. The dmso molecules are grouped into three types of coordination, strong κO-terminal, medium μ2O-bridging, or medium/weak μ3O-bridging, depending on which dimercury(I) ion(s) in the entity they coordinate to.

An overview of eight- and nine-coordinate N-donor solvated lanthanoid(III) and actinoid(III) ions

The use of replacement lanthanoid ions in actinoid chemistry is commonplace, which requires a full understanding of the similarities and differences between the two series. This overview lists, compares and discusses the available crystallographic data for N-donors for the lanthanoids and the actinoids using their trivalent state as a natural starting point for comparison.