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  • 1. Bodor, A.
    et al.
    Toth, I.
    Banyai, I.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Hefter, G. T.
    F-19 NMR study of the equilibria and dynamics of the Al3+/F- system2000In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 39, no 12, p. 2530-2537Article in journal (Refereed)
    Abstract [en]

    A careful reinvestigation by high-field F-19 NMR (470 MHz) spectroscopy has been made of the Al3+/F- system in aqueous solution under carefully controlled conditions of pH, concentration, ionic strength (I), and temperature. The F-19 NMR spectra show five distinct signals at 278 K and I = 0.6 M (TMACl) which have been attributed to the complexes AlFi(3-i)+(aq) with i less than or equal to 5. There was no need to invoke AlFi(OH)(j)((3-i-j)+) mixed complexes in the model under our experimental conditions (pH less than or equal to 6.5), nor was any evidence obtained for the formation of AlF63-(aq) at very high ratios of F-/Al3+. The stepwise equilibrium constants obtained for the complexes by integration of the F-19 signals are in good agreement with literature data given the differences in medium and temperature. In I = 0.6 M TMACl at 278 K and in I = 3 M KCl at 298 K the log K-i values are 6.42, 5.31, 3.99, 2.50, and 0.84 (for species i = 1-5) and 6.35, 5.25, and 4.11 (for species i = 1-3), respectively. Disappearance of the F-19 NMR signals under certain conditions was shown to be due to precipitation. Certain 19F NMR signals exhibit temperature- and concentration-dependent exchange broadening. Detailed line shape analysis of the spectra and magnetization transfer measurements indicate that the kinetics are dominated by F- exchange rather than complex formation. The detected reactions and their rate constants are AlF22+ + *F- reversible arrow AIF*F2+ + F- (k(02) = (1.8 +/- 0.3) x 10(6) M-1 s(-1)), AlF30 + *F- reversible arrow (AlF2F0)-F-* + F- (k(03) = (3.9 +/- 0.9) x 10(6) M-1 s(-1)), and AlF30 + H*F reversible arrow AlF2*F-0 + HF (k(03)(H) = (6.6 +/- 0.5) x 10(4) M-1 s(-1)). The rates of these exchange reactions increase markedly with increasing F- substitution. Thus, the reactions of AlF2+(aq) were too inert to be detected even on the T-1 NMR time scale, while some of the reactions of AlF30(aq) were fast, causing large line broadening. The ligand exchange appears to follow an associative interchange mechanism. The cis-trans isomerization of AlF2+(aq), consistent with octahedral geometry for that complex, is slowed sufficiently to be observed at temperatures around 270 R. Difference between the Al3+/F- system and the much studied Al3+/OH- system are briefly commented on.

  • 2. Farkas, I.
    et al.
    Banyai, I.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Wahlgren, U.
    Grenthe, I.
    Rates and mechanisms of water exchange of UO22+(aq) and UO2(oxalate)F(H2O)(2)(-): A variable-temperature O-17 and F-19 NMR study2000In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 39, no 4, p. 799-805Article in journal (Refereed)
    Abstract [en]

    This study consists of two parts: The first part comprised an experimental determination of the kinetic parameters for the exchange of water between UO2(H2O)(5)(2+) and bulk water, including an ab initio study at the SCF and MP2 levels of the geometry of UO2(H2O)(5)(2+), UO2(H2O)(4)(2+), and UO2(H2O)(6)(2+) and the thermodynamics of their reactions with water. In the second part we made an experimental study of the rate of water exchange in uranyl complexes and investigated how this might depend on inter- and intramolecular hydrogen bond interactions. The experimental studies, made by using O-17 NMR, with Tb3+ as a chemical shift reagent, gave the following kinetic parameters at 25 degrees C: k(ex) = (1.30 +/- 0.05) x 10(6) s(-1); Delta H double dagger = 26.(1) +/- 1.(4) kJ/mol; Delta S double dagger = -40 +/- 5 J/(K mol). Additional mechanistic indicators were obtained from the known coordination geometry of U(VI) complexes with unidentate ligands and from the theoretical calculations. A survey of the literature shows that there are no known isolated complexes of UO22+ with unidentate ligands which have a coordination number larger than 5. This was corroborated by quantum chemical calculations which showed that the energy gains by binding an additional water to UO2(H2O)(4)(2+) and UO2(H2O)(5)(2+) are 29.8 and -2.4 kcal/mol, respectively. A comparison of the change in Delta U for the reactions UO2(H2O)(5)(2+) --> UO2(H2O)(4)(2+) + H2O and UO2(H2O)(5)(2+) + H2O --> UO2(H2O)(6)(2+) indicates that the thermodynamics favors the second (associative) reaction in gas phase at 0 K, while the thermodynamics of water transfer between the first and second coordination spheres, UO2(H2O)(5)(2+) --> UO2(H2O)(4)(H2O)(2+) and UO2(H2O)(5)(H2O)(2+) --> UO2(H2O)(6)(2+), favors the first (dissociative) reaction. The energy difference between the associative and dissociative reactions is small, and solvation has to be included in ab initio models in order to allow quantitative comparisons between experimental data and theory. Theoretical calculations of the activation energy were not possible because of the excessive computing time required. On the basis of theoretical and experimental studies, we suggest that the water exchange in UO2(H2O)(5)(2+) follows a dissociative interchange mechanism. The rates of exchange of water in UO2(oxalate)F(H2O)(2-) (and UO2(oxalate)F-2(H2O)(2-) studied previously) are much slower than in the aquation, k(ex) = 1.6 x 10(4) s(-1), an effect which we assign to hydrogen bonding involving coordinated water and fluoride. The kinetic parameters for the exchange of water in UO2(H2O)(5)(2+) and quenching of photo excited *UO2(H2O)(5)(2+) are very near the same, indicating similar mechanisms.

  • 3.
    Fatih Polat, Muhammed
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hettmanczyk, Lara
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Zhang, Wei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Franzén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    One-Pot, Two-Step Protocol for the Catalytic Asymmetric Synthesis of Optically Active N,O- and O,O-Acetals2013In: ChemCatChem, ISSN 1867-3880, E-ISSN 1867-3899, Vol. 5, no 6, p. 1334-1339Article in journal (Refereed)
  • 4.
    Fischer, Andreas
    et al.
    KTH, Superseded Departments, Chemistry.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Sodium pentafluorouranate(IV) monohydrate, Na[UF5]center dot H2O2004In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. 60, p. I45-I46Article in journal (Refereed)
    Abstract [en]

    Na[UF5]·H2O crystallizes in the orthorhombic space group Pbcn. It contains a uranium(IV) ion, which is coordinated by nine F- ions yielding a tricapped trigonal prism. Some of the F - ions function as bridging ligands coordinating to the Na + ion. The latter is coordinated by four F- ions. Together with two molecules of water of crystallization, a distorted octahedral coordination around Na+ is obtained.

  • 5.
    Fjellander, Ester
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Szabó, Zoltán
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Moberg, Christina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Atropoisomerism in Phosphepines and Azepines2009In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 74, no 23, p. 9120-9125Article in journal (Refereed)
    Abstract [en]

    Free energy barriers to biaryl tropoinversion in metal complexes with tropos phosphepine and azepine ligands were determined by temperature-dependent P-31 NMR inversion-transfer experiments and line shape analysis of the temperature-dependent H-1 NMR spectra, respectively. The barrier in the PdCl2 complex of the azepine ligand was found to be slightly higher than that of the corresponding free ligand. Studies of a tridentate azepine ligand Suggested that Configurational change takes place without prior decoordination from the metal.

  • 6.
    Giesecke, Marianne
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    The protonation state and binding mode in a metal coordination complex from the charge measured in solution by electrophoretic NMR2013In: Analytical Methods, ISSN 1759-9660, E-ISSN 1759-9679, Vol. 5, no 7, p. 1648-1651Article in journal (Refereed)
    Abstract [en]

    We measured with high accuracy the effective charge of a uranium (VI)-AMP complex by electrophoretic NMR (eNMR). Using the same method, the degree of counterion association is also assessed which leads to a quantitative determination of the nominal charge which then provides the degree of ligand deprotonation in the complex. This demonstrates a new application of eNMR for resolving structural details of supramolecular complexes.

  • 7. Johansson, A.
    et al.
    Roman, M.
    Seisenbaeva, G. A.
    Kloo, Lars A.
    KTH, Superseded Departments, Chemistry.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Kessler, V. G.
    The solution thermolysis approach to molybdenum(V) alkoxides: synthesis, solid state and solution structures of the bimetallic alkoxides of molybdenum(V) and niobium(V), tantalum(V) and tungsten(VI)2000In: Journal of the Chemical Society-Dalton Transactions, ISSN 0300-9246, no 3, p. 387-394Article in journal (Refereed)
    Abstract [en]

    No complex formation can be observed between molybdenum(VI) oxoalkoxides and the alkoxides of niobium(V) or tantalum(V) at room temperature. The bimetallic derivatives of molybdenum(V), Mo4M2O8((OPr)-Pr-i)(14), where M=Nb 1 and Ta 2, were instead isolated on cooling from the solutions of the isopropoxides in toluene subjected to a short-time reflux. The X-ray single crystal study showed both 1 and 2 to be built of ((PrO)-Pr-i)(3)M(mu-(OPr)-Pr-i)(3)MoO(mu-O)(2)MoO(mu-(OPr)-Pr-i)(2)MoO(mu-O)(2)MoO(mu-(OPr)-Pr-i)(3)M((OPr)-Pr-i)(3) non-linear chain molecules with 2 Mo-Mo bonds (2.5836(8) Angstrom) and short but non-bonding Mo-M distances (3.1791(8) Angstrom for 1 and 3.1746(8) Angstrom for 2). According to NMR and EXAFS data this structure becomes very fluxional or might even be partially broken into homometallic components in hydrocarbon solutions. The oxidation of 2 with traces of oxygen leads to the formation of Mo3Ta2O8((OPr)-Pr-i)(10) 3. Compound 3 can be isolated in a pure form from the reaction of MoO((OPr)-Pr-i)(4) with Ta((OPr)-Pr-i)(4)(OMe) 6: the presence of methoxide ligands leads to the formation of additional oxoligands via non-reductive thermolysis leading to the formation of a (CH3)(2)C(OMe)(2) ketal as organic byproduct. The molecules of 3 are 5-member rings with a MoO(mu-O)(2)MoO fragment in the basis (Mo-Mo 2.5730(13) Angstrom), coupled to two (mu-(OPr)-Pr-i)(2)Ta((OPr)-Pr-i)(3) fragments that are joined together by an oxomolybdate ligand (mu-O)(2)MoO2. According to NMR-spectroscopic data the aggregate is preserved and rigid in solution. Mo4Ta4O16((OPr)-Pr-i)(12) 4 was found to be one of the products of complete oxidation of 2 (and 3) on prolonged contact with dry oxygen. The thermal treatment of the solutions of MoO((OPr)-Pr-i)(4) and WO((OPr)-Pr-i)(4) in toluene yields (Mo4O8)-O-V(Mo,W)O-VI(2)2((OPr)-Pr-i)(12) 5 with a molecular structure very close to its homometallic analog Mo6O10((OPr)-Pr-i)(12). The complete X-ray single crystal study was carried out for the sample of 5 with (Mo4O8)-O-V(Mo0.45W0.55)O-VI(2)2((OPr)-Pr-i)(12) composition.

  • 8. Moll, H.
    et al.
    Reich, T.
    Hennig, C.
    Rossberg, A.
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Grenthe, I.
    Solution coordination chemistry of uranium in the binary UO22+-SO42- and the ternary UO22+-SO42--OH- system2006In: Radiochimica Acta, ISSN 0033-8230, E-ISSN 2193-3405, Vol. 88, no 11-sep, p. 559-566Article in journal (Refereed)
    Abstract [en]

    The structure and reaction dynamics in the systems UO22+-SO42- and UO22+-SO42--OH- were investigated using EXAFS and O-17-NMR spectroscopy. Uranium Lm edge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. In solution, this is characterized by an U-S distance of 3.11 Angstrom. Approximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Angstrom. The kinetics in the binary uranyl sulfate system can be described by four dominant exchange reactions: (1) UO22++SO(4)(2-)reversible arrow UO2SO4(k(1)), (2) U*O-2(2+)+UO(2)SO(4)reversible arrowU*O2SO4+UO22+(k(2)), (3) UO22++UO2(SO4)(2)(2-)reversible arrow 2UO(2)SO(4)(k(3)), and (4) UO2SO4+SO42-reversible arrowUO2(SO4)(2)(2-)(k(4)). These reactions have rate constants indicating that the exchange is not of the simple Eigen-Wilkins type. Ternary uranyl sulfate hydroxide species were characterized by their O-17 chemical shift and by potentiometry. There are no separate signals for the possible isomers of the ternary species indicating that they are in fast exchange with each other.

  • 9. Moll, H.
    et al.
    Reich, T.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    The hydrolysis of dioxouranium(VI) investigated using EXAFS and O-17-NMR2000In: Radiochimica Acta, ISSN 0033-8230, E-ISSN 2193-3405, Vol. 88, no 7, p. 411-415Article in journal (Refereed)
    Abstract [en]

    The structure of dioxouranium(VI) as a function of pH at different (CH3)(4)N-OH concentrations has been investigated with the aid of U L-III-edge EXAFS. Polynuclear hydroxo species were identified by an U-U interaction at 3.80(8) Angstrom at pH = 4.1. The precipitate formed at pH = 7 has a schoepite like structure. In solution at high pH [0.5 M (CH3)(4)N-OH], the EXAFS data are consistent with the formation of a monomeric four coordinated uranium(VI) hydroxide complex UO2(OH)(4)(2-) of octahedral geometry. The first shell contains two O atoms with a U=O distance of 1.83(o) Angstrom, and four O atoms were identified at a U-O distance of 2.26(5) Angstrom. In strong alkaline solutions [>1 M (CH3)(4)N)-OH],O-17-NMR spectra indicate the presence of two species, presumably UO2(OH)(4)(2-) and UO2(OH)(5)(3-), the latter in low concentration, which are in rapid equilibrium with one another at 268 K in aqueous solution.

  • 10.
    Mueller, Katharina
    et al.
    Helmholtz Zentrum Dresden Rossendorf, Inst Resource Ecol, Bautzner Landstr 400, D-01328 Dresden, Germany..
    Szabo, Zoltan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Organic chemistry.
    Zhang, Xiaobin
    Univ Manitoba, Dept Chem, 144 Dysart Rd, Winnipeg, MB R3T 2N2, Canada..
    Interdisciplinary Round-Robin Test on Molecular Spectroscopy of the U(VI) Acetate System2019In: ACS Omega, ISSN 2470-1343, Vol. 4, no 5, p. 8167-8177Article in journal (Refereed)
    Abstract [en]

    A comprehensive molecular analysis of a simple aqueous complexing system. U(VI) acetate. selected to be independently investigated by various spectroscopic (vibrational, luminescence, X-ray absorption, and nuclear magnetic resonance spectroscopy) and quantum chemical methods was achieved by an international round-robin test (RRT). Twenty laboratories from six different countries with a focus on actinide or geochemical research participated and contributed to this scientific endeavor. The outcomes of this RRT were considered on two levels of complexity: first, within each technical discipline, conformities as well as discrepancies of the results and their sources were evaluated. The raw data from the different experimental approaches were found to be generally consistent. In particular, for complex setups such as accelerator-based X-ray absorption spectroscopy, the agreement between the raw data was high. By contrast, luminescence spectroscopic data turned out to be strongly related to the chosen acquisition parameters. Second, the potentials and limitations of coupling various spectroscopic and theoretical approaches for the comprehensive study of actinide molecular complexes were assessed. Previous spectroscopic data from the literature were revised and the benchmark data on the U(VI) acetate system provided an unambiguous molecular interpretation based on the correlation of spectroscopic and theoretical results. The multimethodologic approach and the conclusions drawn address not only important aspects of actinide spectroscopy but particularly general aspects of modern molecular analytical chemistry.

  • 11. Palladino, Giuseppe
    et al.
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Grenthe, Ingmar
    Structure, equilibrium and ligand exchange dynamics in the binary and ternary dioxouranium(VI)-ethylenediamine-N,N '-diacetic acid-fluoride system: a potentiometric, NMR and X-ray crystallographic study2006In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 43, p. 5176-5183Article in journal (Refereed)
    Abstract [en]

    The structure, thermodynamics and kinetics of the binary and ternary uranium(VI)-ethylenediamine- N,N'-diacetate (in the following denoted EDDA) fluoride systems have been studied using potentiometry, H-1, F-19 NMR spectroscopy and X-ray diffraction. The UO22+ - EDDA system could be studied up to - log[H3O+] = 3.4 where the formation of two binary complexes UO2(EDDA)(aq) and UO2(H(3)EDDA)(3+) were identified, with equilibrium constants log beta(UO(2)EDDA) = 11.63 +/- 0.02 and log beta(UO(2)H(3)EDDA(3+)) = 1.77 +/- 0.04, respectively. In the ternary system the complexes UO2(EDDA) F-, UO2(EDDA)(OH)(-) and (UO2)(2)(mu-OH)(2)(HEDDA)(2)F-2(aq) were identified; the latter through F-19 NMR. H-1 NMR spectra indicate that the EDDA ligand is chelate bonded in UO2(EDDA)(aq), UO2(EDDA) F- and UO2(EDDA)(OH)(-) while only one carboxylate group is coordinated in UO2(H(3)EDDA)(3+). The rate and mechanism of the fluoride exchange between UO2(EDDA) F- and free fluoride was studied by F-19 NMR spectroscopy. Three reactions contribute to the exchange; (i) site exchange between UO2(EDDA) F- and free fluoride without any net chemical exchange, (ii) replacement of the coordinated fluoride with OH- and (iii) the self dissociation of the coordinated fluoride forming UO2(EDDA)(aq); these reactions seem to follow associative mechanisms. H-1 NMR spectra show that the exchange between the free and chelate bonded EDDA is slow and consists of several steps, protonation/deprotonation and chelate ring opening/ring closure, the mechanism cannot be elucidated from the available data. The structure (UO2)(2)(EDDA)(2)(mu-H(2)EDDA) was determined by single crystal X-ray diffraction and contains two UO2( EDDA) units with tetracoordinated EDDA linked by H(2)EDDA in the zwitterion form, coordinated through a single carboxylate oxygen from each end to the two uranium atoms. The geometry of the complexes indicates that there is no geometric constraint for an associative ligand substitution mechanism.

  • 12.
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Multinuclear NMR studies of the interaction of metal ions with adenine-nucleotides2008In: Coordination chemistry reviews, ISSN 0010-8545, E-ISSN 1873-3840, Vol. 252, no 21-22, p. 2362-2380Article, review/survey (Refereed)
    Abstract [en]

    It is well-known that metal ion complexes are essential in various biological systems, including those with adenosine nucleotides which are substrates for a large number of enzymatic processes. The interactions of various metal ions with adenosine nucleotides have been intensively studied by multinuclear NMR spectroscopy. Nucleotides are polydentate ligands with various potential binding sites, including nitrogen atoms on the purine base, hydroxyl groups on the ribose sugar, and negatively charged oxygen atoms in the phosphate group. Depending on the experimental conditions (e.g. pH, concentration range, etc.) and on the size and nature of the metal ions, monodentate, or multidentate coordination to these donor atoms are possible. The review focuses on the applications of different NMR techniques in identifying the stoichiometry and the mode of metal binding in complexes formed with the most important adenosine nucleotides, like adenosine-5'-mono-, di- and triphosphates (AMP, ADP and ATP). Ligand exchange dynamics for some metal ion complexes are also presented.

  • 13.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Structure, equilibrium and ligand exchange dynamics in the binary and ternary dioxouranium(VI)-glyphosate-fluoride system. A multinuclear NMR study2002In: Journal of the Chemical Society. Dalton Transactions, ISSN 1472-7773, E-ISSN 1364-5447, no 22, p. 4242-4247Article in journal (Refereed)
    Abstract [en]

    Complex formation in the binary and ternary uranium(VI)-glyphosate-fluoride systems was investigated with the aid of multinuclear NMR spectroscopy. The stoichiometry and the equilibrium constants of the different complexes in both systems are based on the integral values of the coordinated and free ligands in the H-1-, F-19-, P-31- and O-17-NMR spectra. These were measured at different uranium(II) concentrations, varying the total ligand concentrations (glyphosate and/or fluoride) in the pH range of 7-10 using a NaClO4 medium at constant sodium concentration, [Na+] = 1.00 M. Tridentate and monodentate coordination has been found for the glyphosate ligand. The proposed structures are based on other spectral parameters ( chemical shifts, homo- and heteronuclear couplings) and confirmed by two-dimensional homo- and heteronuclear correlation spectra. The spectra indicate the formation of several isomers for complexes 2 and 4, which differ from one another in the position of the non-chelated glyphosate. The numerical value of the stepwise stability constants for the non-chelated glyphosates in the binary complexes 4 (log K=12) and 5 (log K=11) falls between the formation constants for U(VI) with PO43- and HPO42-, that is an independent confirmation of the magnitude of the latter, but also a strong indication that complex formation with phosphate/phosphonate through a single oxygen bond is very strong. The line widths of the fluoride signals in the ternary complexes are independent of the free ligand concentrations, and from these similar external fluoride exchange rate, k(obs1)= 10 +/- 2 s(-1) can be calculated as observed for other U(VI) ternary complexes. The exchange between the coordinated and the free glyphosate was studied by 1D H-1 magnetization transfer experiments. From these an inter-molecular ligand exchange rate, k(obs2)= 0.69 +/- 0.03 s(-1), and a faster intra-molecular exchange rate for the methylene protons can also be calculated, k(obs3) = 2.00 +/- 0.21 s(-1). The latter is probably a result of consecutive ring openings/chelate formation prior to the dissociation of the ligand.

  • 14.
    Szabo, Zoltan
    et al.
    KTH, Superseded Departments, Chemistry.
    Fischer, Andreas
    KTH, Superseded Departments, Chemistry.
    Redetermination of dipotassium diuranyl tris(oxalate) tetrahydrate2002In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. 58, p. I56-I58Article in journal (Refereed)
    Abstract [en]

    The redetermined structure of K-2 (UO2)(2)(C2O4)(3).4H(2)O shows significantly improved precision of the positional and displacement parameters. Linear uranyl cations are connected by tetradentate bridging oxalate groups yielding a two-dimensional network. These nets are stacked to form the crystal structure.

  • 15.
    Szabo, Zoltan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Csoregh, I.
    Combinatorial multinuclear NMR and X-ray diffraction studies of uranium(VI)-nucleotide complexes2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 43, p. 15236-15247Article in journal (Refereed)
    Abstract [en]

    The complex formation of uranium(VI) with four nucleoticles, adenosine- (AMP), guanosine(GMP), uridine- (UMP), and cyticline-monophosphate (CMP), has been studied in the alkaline pH range (8.5-12) by H-1, P-31, C-13, and O-17 NMR spectroscopy, providing spectral integral, chemical shift, homo and heteronuclear coupling, and diffusion coefficient data. We find that two and only two complexes are formed with all ligands in the investigated pH region independently of the total uranium(VI) and ligand concentrations. Although the coordination of the 5'-phosphate group and the 2'- and 3'-hydroxyl groups of the sugar unit to the uranyl ions is similar to that proposed earlier (Feldman complex), the number and the structures of the complexes are different. The uranium-to-nucleotide ratio is 6:4 in one of the complexes and 3:3 in the other one, as unambiguously determined by a combinatorial approach using a systematic variation of the ratio of two ligands in ternary uranium(VI)-nucleotide systems. The structure of the 3:3 complex has been determined by single-crystal diffraction as well, and the results confirm the structure proposed by NMR in aqueous solution. The results have important implications on the synthesis of oligonucleotides.

  • 16.
    Szabo, Zoltan
    et al.
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    Potentiometric and multinuclear NMR study of the binary and ternary uranium(VI)-L-fluoride systems, where L is alpha-hydroxycarboxylate or glycine2000In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 39, no 22, p. 5036-5043Article in journal (Refereed)
    Abstract [en]

    Equilibria, structures, and ligand-exchange dynamics in binary and ternary U(VI)-L-F- systems, where L is glycolate, alpha -hydroxyisobutyrate, or glycine, have been investigated in 1.0 M NaClO4 by potentiometry and H-1, O-17, and F-19 NMR spectroscopy. L may be bonded in two ways: either through the carboxylate end or by the formation of a chelate. In the glycolate system, the chelate is formed by proton dissociation from the -alpha hydroxy group at around pH 3, indicating a dramatic increase, a factor of at least 10(13), of its dissociation constant on coordination to uranium(VI). The L exchange in carboxylate-coordinated UO2LF32- follows an Eigen-Wilkins mechanism, as previously found for acetate. The water exchange rate, k(aq) = 4.2 x 10(5) s(-1), is in excellent agreement with the value determined earlier for UO22+(aq). The ligand-exchange dynamics of UO2(O-CH2-COO)(2)F-3 and the activation parameters for the fluoride exchange in D2O (k(obs) = 12 s(-1), DeltaH(double dagger) = 45.8 +/- 2.2 kJ mol(-1), and DeltaS(double dagger) = -55.8 +/- 3.6 J K-1 mol(-1)) are very similar to those in the corresponding oxalate complex, with two parallel pathways, one for fluoride and one for the alpha -oxocarboxylate. The same is true for the L exchange in UO2(O-CH2-COO)(2)(2-) and UO2(oxalate)(2)(2-), The exchange of alpha -oxocarboxylate takes place by a proton-assisted chelate ring opening followed by dissociation. Because we cannot decide if there is also a parallel H+-independent pathway, only an upper limit for the rate constant, k(1) < 1,2 s(-1), can be given. This value is smaller than those in previously studied ternary systems. Equilibria and dynamics in the ternary uranium(VI)-glycine-fluoride system, investigated by F-19 NMR spectroscopy, indicate the formation of one major ternary complex, UO2LF32- and one binary complex, UO2L2 (L = H2N-CH2COO-), with chelate-bonded glycine; log beta>(*) over bar * (9) = 13.80 +/- 0.05 for the equilibrium UO22+ + H2N-CH2COO- + 3F(-) = UO2(H2N-CH2COO)F-3(2-) and log beta>(*) over bar * (11) = 13.0 +/- 0.05 for the reaction UO22+ + 2H(2)N-CH2COO- = UO2(H2N-CH2COO)(2). The glycinate exchange consists of a ring opening followed by proton-assisted steps. The rate of ring opening, 139 +/- 9 s(-1), is independent of both the concentration of H+ and the solvent, H2O or D2O.

  • 17.
    Szabo, Zoltan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    (17)O NMR study of the oxygen exchange between uranyl(VI) oxygen and water oxygen in acidic and strongly alkaline solutions2011In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 242, p. 102-NUCL-Article in journal (Other academic)
  • 18.
    Szabo, Zoltan
    et al.
    KTH, Superseded Departments (pre-2005), Chemistry.
    Grenthe, Ingmar
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    NUCL 118-Multinuclear NMR study of the structure and ligand exchange dynamics of uranium(VI) complexes2008In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 235Article in journal (Other academic)
  • 19.
    Szabo, Zoltan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    On the Mechanism of Oxygen Exchange Between Uranyl(VI) Oxygen and Water in Strongly Alkaline Solution as Studied by O-17 NMR Magnetization Transfer2010In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 49, no 11, p. 4928-4933Article in journal (Refereed)
    Abstract [en]

    The mechanism, rate constant, and activation parameters for the exchange between uranyl(VI)) oxygen and water oxygen in tetramethyl ammonium hydroxide solution, TMA-OH, have been determined using O-17 NMR magnetization transfer technique. In the concentration range investigated, the predominant complex is UO2(OH)(4)(2-). The experimental rate equation, rate = k(ex)[TMA-OH](free)[U(VI)](2)(total) indicates that the exchange takes place via a binuclear complex or transition state with the stoichiometry [(UO2(OH)(4)(2-))(UO2(OH)(5)(3-)]. The rate-determining step most likely takes place between the axial "yl" oxygens and the equatorial hydroxides. The experimental Gibbs energy of activation, Delta G(double dagger) = 60.8 +/- 2.4 kJ/mol is in good agreement with the value, Delta A(double dagger) approximate to Delta G(double dagger) = 52.3 +/- 5.4 kJ/mol, found by Buhl and Schreckenbach in a recent Car-Parrinello molecular dynamics study, indicating that their proposed "shuttle" mechanism may be applicable also on the proposed binuclear transition state.

  • 20.
    Szabo, Zoltan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Grenthe, Ingmar
    Reactivity of the yl-bond in Uranyl(VI) complexes. 1. Rates and mechanisms for the exchange between the trans-dioxo oxygen atoms in (UO2)(2)(OH)(2)(2+) and mononuclear UO2(OH)(n)(2-n) complexes with solvent water2007In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 46, no 22, p. 9372-9378Article in journal (Refereed)
    Abstract [en]

    The stoichiometric mechanism, rate constant, and activation parameters for the exchange of the yl-oxygen atoms in the dioxo uranium(VI) ion with solvent water have been studied using O-17 NMR spectroscopy. The experimental rate equation, -v = k(2obs)[ UO22+](tot)(2)/[H+](2), is consistent with a mechanism where the first step is a rapid equilibrium 2U(17) O-2(2+) + 2H(2)O reversible arrow ((UO2)-O-17)(2)(OH)(2)(2+) + 2H(+), followed by the rate-determining step ((UO2)-O-17)(2)(OH)(2)(2+) + H2O reversible arrow (UO2)(2)(OH)(2) (2+) + H-2 170, where the back reaction can be neglected because the 170 enrichment in the water is much lower than in the uranyl ion. This mechanism results in the following rate equation V = d[(UO2)(2)(OH)(2)(2+) ]/dt= k(2,2)[(UO2)(2)(OH)(2)(2+)] = k2,2*beta 2.2[ UO22+](2)/[H+]2; with k(2.2) = (1.88 +/- 0.22) x 10(4) h(-1), corresponding to a half-life of 0.13 s, and the activation parameters triangle h4 = 119 +/- 13 kJ mol(-1) and triangle S* = 81 +/- 44 J mol(-1) K-1. *beta 2.2 is the equilibrium constant for the reaction 2UO(2)(2+) + 2H(2)O reversible arrow (UO2)(2)(OH)(2)(2+) + 2H(+). The experimental data show that there is no measurable exchange of the yl-oxygen in UO22+, UO2(OH)(+), and UO2(OH)(4)(2-)/ UO2(OH)(5)(3-), indicating that yl-exchange only takes place in polynuclear hydroxide complexes. There is no yl-exchange in the ternary complex (UO2)(2)(mu-OH)2(()F)(2)(oxalate)(2)(4-), indicating that it is also necessary to have coordinated water in the first coordination sphere of the binuclear complex, for exchange to take place. The very large increase in lability of the yl-bonds in (UO2)(2)(OH)(2)(2+) as compared to those of the other species is presumably a result of proton transfer from coordinated water to the yl-oxygen, followed by a rapid exchange of the resulting OH group with the water solvent. Yl-exchange through photochemical mediation is well-known for the uranyl(VI) aquo ion. We noted that 4there was no photochemical exchange in UO2(CO3)(3)(4) whereas there was a slow exchange or photo reduction in the UO2(OH)(4)(2-) / UO2(OH)(5)(3)- system that eventually led to the appearance of a black precipitate, presumably UO2.

  • 21.
    Szabo, Zoltan
    et al.
    KTH, Superseded Departments, Chemistry.
    Moll, H.
    Grenthe, I.
    Structure and dynamics in the complex ion (UO2)(2)(CO3)(OH)(3)(-)2000In: Journal of the Chemical Society. Dalton Transactions, ISSN 1472-7773, E-ISSN 1364-5447, no 18, p. 3158-3161Article in journal (Refereed)
    Abstract [en]

    The structure and ligand exchange dynamics of the ternary complex (UO2)(2)(CO3)(OH)(3)(-) have been investigated by EXAFS and NMR spectroscopy. Very broad signals can be observed in both the C-13 and the O-17 NMR spectra. The EXAFS data show the presence of 1.3 +/- 0.3 short uranium-oxygen distances at 2.26 Angstrom, consistent with single bonded hydroxide and 3.9 +/- 0.6 distances at 2.47 Angstrom for the other ligands in the first co-ordination shell. There is also evidence for a U ... U interaction at 3.90 Angstrom. Based on the EXAFS and NMR data we suggest the presence of three isomers with different bridge arrangements, the dominant one, C, contains 80% of the uranium and the minor ones A and B, 5 and 15%, respectively. The ligand exchange reactions between these isomers are slow. The NMR data indicate that the main reactions involve intramolecular exchanges between isomers with different positions of the non-bridging ligands in A, B and C. We suggest that these take place through water exchange as discussed earlier for other ternary uranium(VI) complexes.

  • 22.
    Szabo, Zoltan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Toraishi, T.
    Vallet, V.
    Grenthe, I.
    Solution coordination chemistry of actinides: Thermodynamics, structure and reaction mechanisms2006In: Coordination chemistry reviews, ISSN 0010-8545, E-ISSN 1873-3840, Vol. 250, no 08-jul, p. 784-815Article, review/survey (Refereed)
    Abstract [en]

    The emphasis of this review is on the combination of experimental and theoretical methods to obtain microscopic information on the chemistry of actinides in aqueous solution. A brief discussion is given of some important experimental methods that provide information on the equilibrium constants and constitution of actinide complexes in solution, their structure and the rate and mechanism of ligand substitution reactions. The microscopic perspective is provided by a comparison of experimental data with those obtained using quantum chemical methods; the emphasis is here on structure and reaction mechanisms. Most of the experimental data refer to the chemistry of uranium, thorium and curium, but this information can be generalized to other actinides as their chemistry is often very similar in a given oxidation state. The first step in the analysis of complex formation in solution is based on equilibrium analytical methods; the discussion is here focused on those requiring macro amounts of actinides, as these are necessary in the methods used to obtain structure (large angle X-ray scattering, extended X-ray absorption spectroscopy and NMR) and dynamic (NMR, relaxation and stopped-flow methods) information. Finally, some comments are made on how the molecular understanding of complex formation between UO2 (2+) and small ligands may be of importance in naturally occurring ligands like humic and fulvic acids and biomolecules, such as amino acids, proteins and nucleotides.

  • 23.
    Szabo, Zoltan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Vallet, Valerie
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Structure and dynamics of binary and ternary lanthanide(III) and actinide(III) tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione] (TTA) complexes. Part 2, the structure and dynamics of binary and ternary complexes in the Y(III)/Eu(III) -TTA - tributylphosphate (TBP) system in chloroform as studied by NMR spectroscopy2010In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, no 45, p. 10944-10952Article in journal (Refereed)
    Abstract [en]

    The stoichiometric reaction mechanisms, rate constants and activation parameters for inter-and intramolecular ligand exchange reactions in the binary Y/Eu(TTA)(3)(OH2)(2)-HTTA and the ternary Y/Eu(TTA)(3)(OH2)(2)-TBP systems have been studied in chloroform using H-1 and P-31 NMR methods. Most complexes contain coordinated water that is in very fast exchange with water in the chloroform solvent. The exchange reactions involving TTA/HTTA and TBP are also fast, but can be studied at lower temperature. The rate constant and activation parameters for the intramolecular exchange between two structure isomers in Y(TTA)(3)(OH2)(2) and Y(TTA)(3)(TBP)(OH2) were determined from the line-broadening of the methine protons in coordinated TTA. The rate equations for the intermolecular exchange between coordinated TTA and free HTTA in both complexes are consistent with a two-step mechanism where the first step is a fast complex formation of HTTA, followed by a rate determining step involving proton transfer from coordinated HTTA to TTA. The rate constants for both the interand intramolecular exchange reactions are significantly smaller in the TBP system. The same is true for the activation parameters in the Y(TTA)(3)(OH2)(2)-HTTA and the ternary Y/Eu(TTA)(3)(TBP)(OH2)-HTTA systems, which are Delta H-not equal = 71.8 +/- 2.8 kJ mol(-1), Delta S-not equal = 62.4 +/- 10.3 J mol(-1) K-1 and Delta H-not equal = 38.8 +/- 0.6 kJ mol(-1), Delta S-not equal = -93.0 +/- 3.3 J mol(-1) K-1, respectively. The large difference in the activation parameters does not seem to be related to a difference in mechanism as judged by the rate equation; this point will be discussed in a following communication. The rate and mechanism for the exchange between free and coordinated TBP follows a two-step mechanism, involving the formation of Y(TTA)(3)(TBP)(2).

  • 24.
    Theveau, Laure
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Bellini, Rosalba
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Dydio, Pawel
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    van der Werf, Angela
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. University of Amsterdam, Netherlands.
    Sander, Robin Afshin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Reek, Joost N. H.
    Moberg, Christina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Cofactor-Controlled Chirality of Tropoisomeric Ligand2016In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 35, no 11, p. 1956-1963Article in journal (Refereed)
    Abstract [en]

    A new tropos ligand with an integrated anion receptor receptor site has been prepared. Chiral carboxylate and phosphate anions that bind in the anion receptor unit proved capable of stabilizing chiral conformations of the achiral flexible bidentate biaryl phosphite ligand, as shown by variable temperature H-1 and P-31 NMR spectroscopical studies of palladium(0) olefin complexes. Palladium allyl complexes of the supramolecular ligand-chiral cofactor assemblies catalyzed asymmetric allylic substitutions of rac-(E)-1,3-diphenyl-2-propenyl carbonate and rac-3-cyclohexenyl carbonate with malonate and benzylamine as nucleophiles to provide nonracemic products. Although moderate enantioselectivities were observed, (ee:s up to 66%), the results confirm the ability of the anionic guests to affect the conformation of the ligand.

  • 25.
    Tilliet, Mélanie
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Frölander, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Zetterberg, Krister
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Moberg, Christina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Influence of Ligand Secondary Interactions on Dynamic Processes in Alkene Ir ComplexesManuscript (Other academic)
  • 26. Toraishi, T.
    et al.
    Farkas, I.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    Complexation of Th(IV) and various lanthanides(III) by glycolic acid; potentiometric, C-13-NMR and EXAFS studies2002In: Journal of the Chemical Society. Dalton Transactions, ISSN 1472-7773, E-ISSN 1364-5447, no 20, p. 3805-3812Article in journal (Refereed)
    Abstract [en]

    The complex formation of tetravalent thorium and various trivalent lanthanides by glycolate HOCH2CO2- = A(-), has been investigated by potentiometry, C-13-NMR spectroscopy and EXAFS. The potentiometric data were used to deduce the stoichiometry and equilibrium constants for the reactions pM(n+) (aq) + rA(-) reversible arrow M(p)H(-q)A(r)(np - q - r) + qH(+) at 25 degreesC, in an ionic medium with a constant concentration of Na+ equal to 3.00 M. Mononuclear complexes Th(HOCH2CO2-)(n); n = 1-4, were identified in the -log[H+] range 2.5-4.5. The equilibrium constants of these complexes obtained using a least-squares analysis of the experimental data agree well with previously published information; these test solutions also contain dinuclear ternary complexes Th(2)H(-2)A(r), r = 2, 4 and 6. The complex formation in the pH range 5-10 was studied at high and constant concentrations of glycolate, 0.50, 0.75 and 1.0 M, respectively. Under these conditions, in addition to the dinuclear species, also tetranuclear complexes M(4)H(-q)A(8) are formed, where q varies from 6 to 13 and 6 to 8 for the Th(IV) and Ln(III) systems, respectively. C-13 NMR spectra show that coordinated and free glycolate are in fast exchange at pH 4.5, while at higher pH there are two separate narrow peaks both in the CH2 and CO2- regions for the coordinated ligand, indicating slow exchange between two equally populated sites. The peak integrals correspond to two bonded ligands per metal for both Th(IV) and Ln(III). EXAFS data were used to deduce bond distances within the tetranuclear Th complexes. These data together with the NMR-data indicate that the tetranuclear complexes have a cubane-like core M-4 (OCH2CO2)(4) to which additional glycolate, oxyacetate and hydroxide ligands are coordinated. The identification of new structure and bonding characteristics of alpha-hydroxycarboxylates, in particular at higher pH, may be used to explore new separation schemes between actinides in different oxidation states, but also for group separations between lanthanide(III) and actinide(III) ions.

  • 27. Vallet, V.
    et al.
    Moll, H.
    Wahlgren, U.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    Structure and bonding in solution of dioxouranium(VI) oxalate complexes: Isomers and intramolecular ligand exchange2003In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 42, no 6, p. 1982-1993Article in journal (Refereed)
    Abstract [en]

    Structural isomers of [UO2(oxalate)(3)](4-), [UO2(oxalate)F-3](3-), [UO2(oxalate)(2)F](3-), and [UO2(oxalate)(2)(H2O)](2-) have been studied by using EXAFS and quantum chemical ab initio methods. Theoretical structures and their relative energies were determined in the gas phase and in water using the CPCM model. The most stable isomers according to the quantum chemical calculations have geometries consistent with the EXAFS data, and the difference between measured and calculated bond distances is generally less than 0.05 Angstrom. The complex [UO2(oxalate)(3)](4-) contains two oxalate ligands forming five-membered chelate rings, while the third is bonded end-on to a single carboxylate oxygen. The most stable isomer of the other two complexes also contains the same type of chelate-bonded oxalate ligands. The activation energy for ring opening in [UO2(oxalate)F-3](3-), DeltaU(double dagger) = 63 kJ/mol, is in fair agreement with the experimental activation enthalpy, DeltaH(double dagger) = 45 +/- 5 kJ/mol, for different [UO2(PiCOlinate)F-3](2-) complexes, indicating similar ring-opening mechanisms. No direct experimental information is available on intramolecular exchange in [UO3(oxalate)(3)](4-). The theoretical results indicate that it takes place via the tris-chelated intermediate with an activation energy of AV = 38 kJ/mol; the other pathways involve multiple steps and have much higher activation energies. The geometries and energies of dioxouranium(VI) complexes in the gas phase and solvent models differ slightly, with differences in bond distance and energy of typically less than 0.06 Angstrom and 10 kJ/mol, respectively. However, there might be a significant difference in the distance between uranium and the leaving/entering group in the transition state, resulting in a systematic error when the gas-phase geometry is used to estimate the activation energy in solution. This systematic error is about 10 kJ/mol and tends to cancel when comparing different pathways.

  • 28. Vallet, V.
    et al.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Grenthe, Ingmar
    KTH, Superseded Departments, Chemistry.
    Experimental and quantum chemical studies of structure and reaction mechanisms of dioxouranium(VI) complexes in solution2004In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 22, p. 3799-3807Article in journal (Refereed)
    Abstract [en]

    This perspective article describes the combination of experimental data and quantum chemical methods for the determination of structure and reaction mechanisms of uranyl( VI) complexes in aqueous solution. The first part assesses the accuracy of the chemical and thermodynamic properties of solvated uranyl( VI) complexes as obtained by various quantum chemical methods. The second part discusses structure determination, mechanisms for ligand exchange and the lability of coordinated water molecules for various uranyl( VI) complexes using a combination of NMR and quantum chemical data.

  • 29. Vallet, V.
    et al.
    Wahlgren, U.
    Schimmelpfennig, B.
    Moll, H.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    Solvent effects on uranium(VI) fluoride and hydroxide complexes studied by EXAFS and quantum chemistry2001In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 40, no 14, p. 3516-3525Article in journal (Refereed)
    Abstract [en]

    The structures of the complexes UO2Fn(H2O)(5-n)(2-n), n = 3-5, have been studied by EXAFS. All have pentagonal bipyramid geometry with U-F of and U-H2O distances equal to 2.26 and 2.48 Angstrom, respectively. On the other hand the complex UO2(OH)(4)(2-) has a square bipyramid geometry both in the solid state and in solution. The structures of hydroxide and fluoride complexes have also been investigated with wave function based and DFT methods in order to explore the possible reasons for the observed structural differences. These studies include models that describe the solvent by using a discrete second coordination sphere, a model with a spherical, or shape-adapted cavity in a conductor-like polarizable continuum medium (CPCM), or a combination of the two. Solvent effects were shown to give the main contribution to the observed structure variations between the uranium(VI) tetrahydroxide and the tetrafluoride complexes. Without a solvent model both UO2(OH)(4)(H2O)(2-) and UO2F4(H2O)(2-) have the same square bipyramid geometry, with the water molecule located at a distance of more than 4 Angstrom from uranium and with a charge distribution that is very near identical in the two complexes. Of the models tested, only the CPCM ones are able to describe the experimentally observed square and pentagonal bipyramid geometry in the tetrahydroxide and tetrafluoride complexes. The geometry and the relative energy of different isomers of UO2F3(H2O)(2)(-) are very similar, indicating that they are present in comparable amounts in solution. All calculated bond distances are in good agreement with the experimental observations, provided that a proper model of the solvent is used.

  • 30. Vallet, V.
    et al.
    Wahlgren, U.
    Schimmelpfennig, B.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    The mechanism for water exchange in UO2(H2O)(5) (2+) and UO2(oxalate)(2)(H2O) (2-), as studied by quantum chemical methods2001In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 123, no 48, p. 11999-12008Article in journal (Refereed)
    Abstract [en]

    The mechanisms for the exchange of water between [UO2(H2O)(5)](2+), [UO2(oxalate)(2)(H2O)](2-), and water solvent along dissociative (D), associative (A) and interchange (1) pathways have been investigated with quantum chemical methods. The choice of exchange mechanism is based on the computed activation energy and the geometry of the identified transition states and intermediates. These quantities were calculated both in the gas phase and with a polarizable continuum model for the solvent. There is a significant and predictable difference between the activation energy of the gas phase and solvent models: the energy barrier for the D-mechanism increases in the solvent as compared to the gas phase, while it decreases for the A- and I-mechanisms. The calculated activation energy, AW, for the water exchange in [UO2(H2O)(5)](2+) is 74, 19, and 21 kJ/mol, respectively, for the D-, A-, and I-mechanisms in the solvent, as compared to the experimental value DeltaH(double dagger) = 26 +/- 1 kJ/mol. This indicates that the D-mechanism for this system can be ruled out. The energy barrier between the intermediates and the transition states is small, indicating a lifetime for the intermediate approximate to 10(-10) s, making it very difficult to distinguish between the A- and I-mechanisms experimentally. There is no direct experimental information on the rate and mechanism of water exchange in [UO2(oxalate)(2)(H2O)](2-)containing two bidentate oxalate ions. The activation energy and the geometry of transition states and intermediates along the D-, A-, and I-pathways were calculated both in the gas phase and in a water solvent model, using a single-point MP2 calculation with the gas phase geometry. The activation energy, AW, in the solvent for the D-, A-, and I-mechanisms is 56, 12, and 53 kJ/mol, respectively. This indicates that the water exchange follows an associative reaction mechanism. The geometry of the A- and I-transition states for both [UO2(H2O)(5)](2+) and [UO2(oxalate)(2)(H2O)](2-) indicates that the entering/leaving water molecules are located outside the plane formed by the spectator ligands.

  • 31. Vallet, V.
    et al.
    Wahlgren, U.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    Rates and mechanism of fluoride and water exchange in UO2F53- and UO2F4(H2O) (2-) studied by NMR spectroscopy and wave function based methods2002In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 41, no 21, p. 5626-5633Article in journal (Refereed)
    Abstract [en]

    The reaction mechanism for the exchange of fluoride in UO2F53- and UO2F4(H2O)(2-) has been investigated experimentally using F-19 NMR spectroscopy at -5 degreesC, by studying the line broadening of the free fluoride, UO2F42-(aq) UO2F53-, and theoretically using quantum chemical methods to calculate the activation energy for different pathways. The new experimental data allowed us to make a more detailed study of chemical equilibria and exchange mechanisms than in previous studies. From the integrals of the different individual peaks in the new NMR spectra, we obtained the stepwise stability constant K-5 = 0.60 +/- 0.05 M-1 for UO2F53-. The theoretical results indicate that the fluoride exchange pathway of lowest activation energy, 71 kJ/mol, in UO2F53- is water assisted. The pure dissociative pathway has an activation energy of 75 kJ/mol, while the associative mechanism can be excluded as there is no stable UO2F64- intermediate. The quantum chemical calculations have been made at the SCF/MP2 levels, using a conductor-like polarizable continuum model (CPCM) to describe the solvent. The effects of different model assumptions on the activation energy have been studied. The activation energy is not strongly dependent on the cavity size or on interactions between the complex and Na+ counterions. However, the solvation of the complex and the leaving fluoride results in substantial changes in the activation energy. The mechanism for water exchange in UO2F4(H2O)(2-) has also been studied. We could eliminate the associative mechanism, the dissociative mechanism had the lowest activation energy, 39 kJ/mol, while the interchange mechanism has an activation energy that is approximately 50 kJ/mol higher.

  • 32. Vallet, Valerie
    et al.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    The structure and bonding of Y, Eu, U, Am and Cm complexes as studied by quantum chemical methods and X-ray crystallography2010In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, no 33, p. 7666-7672Article in journal (Refereed)
    Abstract [en]

    Two isomers of Y/Eu(TTA)(3)(OH2) complexes and their structures were identified by single crystal X-ray diffraction, and their geometry and bond distances were also determined using quantum chemical (QM) methods. The data from the two methods agree very well, suggesting that QM is appropriate for calculating structures for which no experimental data are available. This method was therefore used to determine the structures of U/Am/Cm(TTA)(3)(OH2)(2) both in gas phase and in CPCM models of CCl4, CHCl3, and H2O. In these calculations the metal sites were described using the f-in-core approximation, comparing small- and large-core pseudopotentials (SPP and LPP) with their corresponding segmented basis sets. The difference between the Y/Eu-O bond distances between the LPP and SPP is less than 0.02 angstrom. However, in the actinide complexes the LPP results in larger An-O distances and the difference between the LPP and SPP results decreases from about 0.20 angstrom in the U-complex to 0.05 angstrom in the Am-and 0.04 angstrom in the Cm-complex. The chemical bonding studied by population analysis indicates that there is a significant back bonding in U(TTA)(3)(OH2)(2) from filled orbitals centered on uranium into empty pi* orbitals on coordinated oxygen; there is some evidence of back-bonding also in the americium complex, but a significantly smaller effect in the europium and curium species. The relative energy of the two isomers indicates they may be present in solution in comparable amounts, suggesting the possibility of exchange between them. The X-ray structures suggest two exchange pathways, a topological "twist" mechanism and a site exchange involving the opening of a TTA chelate ring.

  • 33. Vallet, Valerie
    et al.
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Structure and dynamics of binary and ternary lanthanide(III) and actinide(III) tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione] (TTA) - tributylphosphate (TBP) complexes.: Part 3, the structure, thermodynamics and reaction mechanisms of 8-and 9-coordinated binary and ternary Y-TTA-TBP complexes studied by quantum chemical methods2011In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 40, no 13, p. 3154-3165Article in journal (Refereed)
    Abstract [en]

    Possible mechanisms for intermolecular exchange between coordinated and solvent water in the complexes Y(TTA)(3)(OH2)(2) and Y(TTA)(3)(TBP)(OH2) and intermolecular exchange between free and coordinated HTTA in Y(TTA)(3)(OH2)(HTTA) and Y(TTA)(3)(TBP)(HTTA) have been investigated using ab initio quantum chemical methods. The calculations comprise both structures and energies of isomers, intermediates and transition states. Based on these data and experimental NMR data (Part 2) we have suggested intimate reaction mechanisms for water exchange, intramolecular exchange between structure isomers and intermolecular exchange between free HTTA and coordinated TTA. A large number of isomers are possible for the complexes investigated, but only some of them have been investigated, in all of them the most stable geometry is a more or less distorted square anti-prism or bicapped trigonal prism; the energy differences between the various isomers are in general small, less than 10 kJ mol(-1). 9-coordinated intermediates play an important role in all reactions. Y(TTA)(3)(OH2)(3) has three non-equivalent water ligands that can participate in ligand exchange reactions. The fastest of these exchanging sites has a QM activation energy of 18.1 kJ mol(-1), in good agreement with the experimental activation enthalpy of 19.6 kJ mol(-1). The mechanism for the intramolecular exchange between structure isomers in Y(TTA)(3)(OH2)(2) involves the opening of a TTA-ring as the rate determining step as suggested by the good agreement between the QM activation energy and the experimental activation enthalpy 47.8 and 58.3 J mol(-1), respectively. The mechanism for the intermolecular exchange between free and coordinated HTTA in Y(TTA)(3)(HTTA) and Y(TTA)(3)(TBP)(HTTA) involves the opening of the intramolecular hydrogen bond in coordinated HTTA followed by proton transfer to coordinated TTA. This mechanism is supported by the good agreement between experimental activation enthalpies (within parenthesis) and calculated activation energies 68.7 (71.8) and 35.3 (38.8) kJ mol(-1). The main reason for the difference between the two systems is the much lower energy required to open the intramolecular hydrogen bond in the latter. The accuracy of the QM methods and chemical models used is discussed.

  • 34.
    Vallet, Valerie
    et al.
    CNRS, Lab PhLAM, Villeneuve Dascq, France..
    Zanonato, Pier Luigi
    Univ Padua, Dipartimento Sci Chim, Padua, Italy..
    Di Bernardo, Plinio
    Univ Padua, Dipartimento Sci Chim, Padua, Italy..
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Grenthe, Ingmar
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    Experimental and quantum chemical studies of alkali-ion promoted formation of uranyl(VI) peroxide rings and a comparison with similar reactions in 12-crown-5 and 15-crown-5 systems2015In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 249Article in journal (Other academic)
  • 35.
    Zalubovskis, Raivis
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Fjellander, Ester
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Szabó, Zoltán
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Moberg, Christina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Stereochemical Control of Chirally Flexible Phosphepines2007In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, Vol. 2007, no 1, p. 108-115Article in journal (Refereed)
    Abstract [en]

    The barriers to interconversion of the two enantiomeric atropisomers of 6-methoxy-6,7-dihydro-5H-dibenzo[c,e]phosphepine and that of the diastereomeric forms of 6-(-)menthoxy-6,7-dihydro-3H-dibenzo[c,e]phosphepine were determined by NMR spectroscopical methods to be 19.3 and 18.5 kcalmol(-1), respectively, at 298 K. The ratio of the atropisomers was shown to depend on the group bound to phosphorus. Only complexes with two homochiral ligands bound to the each metal center were obtained upon reaction with [Rh(COD)(2)](+) BF4-. The Rh complexes catalyzed the hydrogenation of alpha-acetamidocinnamate. The major isomer of 6-(-)-menthoxy-6,7-dihydro-5H-dibenzo[c,e]phosphepine was found to exhibit higher activity but to afford a product with lower ee than its diastereomer.

  • 36. Zanonato, Pier Luigi
    et al.
    Di Bernardo, Plinio
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Chemical equilibria in the uranyl(VI)-peroxide-carbonate system: identification of precursors for the formation of poly-peroxometallates2012In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 41, no 38, p. 11635-11641Article in journal (Refereed)
    Abstract [en]

    The focus of this study is on the identification of precursors in solution that might act as building blocks when solid uranyl(VI) poly-peroxometallate clusters containing peroxide and hydroxide bridges are formed. The precursors could be identified by using carbonate as an auxiliary ligand that prevented the formation of large clusters, such as the ones found in solids of fullerene type. Using data from potentiometric and NMR (O-17 and C-13) experiments we identified the following complexes and determined their equilibrium constants: (UO2)(2)(O-2)(CO3)(4)(6-), UO2(O-2)CO32-, UO2(O-2)(CO3)(2)(4-), (UO2)(2)(O-2)(CO3)(2)(2-), (UO2)(2)(O-2)(2)(CO3)(2-) and [UO2(O-2)(CO3)(5)(10-). The NMR spectra of the pentamer show that all uranyl and carbonate sites are equivalent, which is only consistent with a ring structure built from uranyl units linked by peroxide bridges with the carbonate coordinated "outside" the ring; this proposed structure is very similar to [UO2(O-2)(oxalate)](5)(10-) identified by Burns et al. (J. Am. Chem. Soc., 2009, 131, 16648; Inorg. Chem., 2012, 51, 2403) in K-10[UO2(O-2)(oxalate)](5)center dot(H2O)(13); similar ring structures where oxalate or carbonate has been replaced by hydroxide are important structure elements in solid poly-peroxometallate complexes. The equivalent uranyl sites in (UO2)(2)(O-2)(2)(CO3)(2-) suggest that the uranyl-units are linked by the carbonate ion and not by peroxide.

  • 37. Zanonato, Pier Luigi
    et al.
    Di Bernardo, Plinio
    Vallet, Valerie
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Alkali-metal ion coordination in uranyl(VI) poly-peroxide complexes in solution. Part 1: the Li+, Na+ and K+ - peroxide-hydroxide systems2015In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, no 4, p. 1549-1556Article in journal (Refereed)
    Abstract [en]

    The alkali metal ions Li+, Na+ and K+ have a profound influence on the stoichiometry of the complexes formed in uranyl(VI)-peroxide-hydroxide systems, presumably as a result of a templating effect, resulting in the formation of two complexes, M[(UO2)(O-2)(OH)](2)(-) where the uranyl units are linked by one peroxide bridge, mu-eta(2)-eta(2), with the second peroxide coordinated "end-on", eta(2), to one of the uranyl groups, and M[(UO2)(O-2)(OH)](4)(3-), with a four-membered ring of uranyl ions linked by mu-eta(2)-eta(2) peroxide bridges. The stoichiometry and equilibrium constants for the reactions: M+ + 2UO(2)(2+) + 2HO(2)(-) + 2H(2)O -> M[(UO2)(O-2)(OH)] 2 - + 4H(+) (1) and M+ + 4UO(2)(2+) + 4HO(2)(-) + 4H(2)O -> M[(UO2)(O-2)(OH)](4)(3-) + 8H(+) (2) have been measured at 25 degrees C in 0.10 M (tetramethyl ammonium/M+)NO3 ionic media using reaction calorimetry. Both reactions are strongly enthalpy driven with large negative entropies of reaction; the observation that Delta H(2) approximate to 2 Delta H(1) suggests that the enthalpy of reaction is approximately the same when peroxide is added in bridging and "end-on" positions. The thermodynamic driving force in the reactions is the formation of strong peroxide bridges and the role of M+ cations is to provide a pathway with a low activation barrier between the reactants and in this way "guide" them to form peroxide bridged complexes; they play a similar role as in the synthesis of crown-ethers. Quantum chemical (QC) methods were used to determine the structure of the complexes, and to demonstrate how the size of the M+-ions affects their coordination geometry. There are several isomers of Na[(UO2)(O-2)(OH)](2)(-) and QC energy calculations show that the ones with a peroxide bridge are substantially more stable than the ones with hydroxide bridges. There are isomers with different coordination sites for Na+ and the one with coordination to the peroxide bridge and two uranyl oxygen atoms is the most stable one.

  • 38. Zanonato, P.L.
    et al.
    Szabó, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Vallet, V.
    Di Bernardo, P.
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Alkali-metal ion coordination in uranyl(VI) poly-peroxo complexes in solution, inorganic analogues to crown-ethers. Part 2. Complex formation in the tetramethyl ammonium-, Li+-, Na+- and K+-uranyl(VI)-peroxide-carbonate systems2015In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, no 37, p. 16565-16572Article in journal (Refereed)
    Abstract [en]

    The constitution and equilibrium constants of ternary uranyl(VI) peroxide carbonate complexes [(UO2)(p)(O-2)(q)(CO3)(r)](2(p-q-r)) have been determined at 0 degrees C in 0.50 M MNO3, M = Li, K, and TMA (tetramethyl ammonium), ionic media using potentiometric and spectrophotometric data; O-17 NMR data were used to determine the number of complexes present. The formation of cyclic oligomers, "[(UO2)(O-2)(CO3)](n)", n = 4, 5, 6, with different stoichiometries depending on the ionic medium used, suggests that Li+, Na+, K+ and TMA ions act as templates for the formation of uranyl peroxide rings where the uranyl-units are linked by mu-eta(2)-eta(2) bridged peroxide-ions. The templating effect is due to the coordination of the M+-ions to the uranyl oxygen atoms, where the coordination of Li+ results in the formation of Li[(UO2)(O-2)(CO3)](4)(7-), Na+ and K+ in the formation of Na/K[(UO2)(O-2)(CO3)](5)(9-) complexes, while the large tetramethyl ammonium ion promotes the formation of two oligomers, TMA[(UO2)(O-2)(CO3)] 5 9-and TMA[(UO2)(O-2)(CO3)](6)(11-). The NMR spectra demonstrate that the coordination of Na+ in the five-and six-membered oligomers is significantly stronger than that of TMA(+); these observations suggest that the templating effect is similar to the one observed in the synthesis of crown-ethers. The NMR experiments also demonstrate that the exchange between TMA[(UO2)(O-2)(CO3)](5)(9-) and TMA[(UO2)(O-2)(CO3)](6)(11-) is slow on the O-17 chemical shift time-scale, while the exchange between TMA[(UO2)(O-2)(CO3)](6)(11-)and Na[(UO2)(O-2)(CO3)](6)(11-) is fast. There was no indication of the presence of large clusters of the type identified by Burns and Nyman (M. Nyman and P. C. Burns, Chem. Soc. Rev., 2012, 41, 7314-7367) and possible reasons for this and the implications for the synthesis of large clusters are briefly discussed.

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