Patric Lindqvist-Reis

Complexation of Europium(III) by Bis(dialkyltriazinyl)bipyridines in 1-Octanol

The present work focuses on highly selective ligands for An(III)/Ln(III) separation: bis(triazinyl)bipyridines (BTBPs). By combining time-resolved laser-induced fluorescence spectroscopy, nanoelectrospray ionization mass spectrometry, vibronic sideband spectroscopy, and X-ray diffraction, we obtain a detailed picture of the structure and stoichiometry of the first coordination sphere of Eu(III)-BTBP complexes in an octanolic solution. The main focus is on the 1:2 complexes because extraction studies revealed that those are the species extracted into the organic phase. The investigations on europium(III) complexes of BTBP with different triazin alkylation revealed differences in the formed complexes due to the bulkiness of the ligands. Because of the vibronic sidebands in the fluorescence spectra, we were able to detect whether or not nitrate ligands are coordinated in the first coordination sphere of the Eu-BTBP complexes. In solution, less sterically demanding BTBP offers enough space for additional coordination of anions and/or solvent molecules to form 9-coordinated Eu-BTBP 1:2 complexes, while bulkier ligands tend to form 8-fold-coordinated structures. We also report the first crystal structure of a Ln-BTBP 1:2 complex and that of its 1:1 complex, both of which are 10-coordinated.

TRLFS study on the complexation of Cm(III) with nitrate in the temperature range from 5 to 200 ◦ C

Abstract The formation of aqueous Cm(III) nitrate complexes is studied in the temperature range from 5 to 200 °C by time resolved laser fluorescence spectroscopy (TRLFS). The experiments are performed in a custom build high pressure and high temperature fluorescence cell. The complex formation is measured at nitrate concentrations ranging from 0.10 to 4.61 mol/kg H2O. The mono- and dinitrate complexes are quantified by peak deconvolution of the fluorescence spectra and the complexation constants are determined as a function of the temperature. The conditional equilibrium constants are extrapolated to zero ionic strength using the specific ion interaction theory (SIT) and the thermodynamic standard state data (ΔrH°m, ΔrS°m, ΔrG°m, ΔrC°p,m) are determined from the temperature dependence of the equilibrium constants at I=0. The equilibrium constants up to 75 °C are well described by the Van´t Hoff equation (ΔrH°m independent of T and ΔrC°p,m=0). Modelling of the data at higher temperatures requires an extended equation including a term for the heat capacity changes (ΔrC°p,m).

Vibrational spectroscopic force field studies of dimethyl sulfoxide and hexakis(dimethyl sulfoxide)scandium(III) iodide, and crystal and solution structure of the hexakis(dimethyl sulfoxide)scandium(III) ion

Hexakis(dimethyl sulfoxide)scandium(III) iodide, [Sc(OS(CH(3))(2))(6)]I(3) contains centrosymmetric hexasolvated scandium(III) ions with an Sc-O bond distance of 2.069(3) angstroms. EXAFS spectra yield a mean Sc-O bond distance of 2.09(1) angstroms for solvated scandium(III) ions in dimethyl sulfoxide solution, consistent with six-coordination. Raman and infrared absorption spectra have been recorded, also of the deuterated compound, and analysed by means of normal coordinate methods, together with spectra of dimethyl sulfoxide. The effects on the vibrational spectra of the weak intermolecular C-H...O interactions and of the dipole-dipole interactions in liquid dimethyl sulfoxide have been evaluated, in particular for the S-O stretching mode. The strong Raman band at 1043.6 cm(-1) and the intense IR absorption at 1062.6 cm(-1) have been assigned as the S-O stretching frequencies of the dominating species in liquid dimethyl sulfoxide, evaluated as centrosymmetric dimers with antiparallel polar S-O groups. The shifts of vibrational frequencies and force constants for coordinated dimethyl sulfoxide ligands in hexasolvated trivalent metal ion complexes are discussed. Hexasolvated scandium(iii) ions are found in dimethyl sulfoxide solution and in [Sc(OSMe(2))(6)]I(3). The iodide ion-dipole attraction shifts the methyl group C-H stretching frequency for (S-)C-H...I(-) more than for the intermolecular (S-)C-H...O interactions in liquid dimethyl sulfoxide.

Grazing incidence (GI) XAFS measurements of Hf(IV) and U(VI) sorption onto mineral surfaces

Surface sensitive grazing incidence XAFS measurements of mineral sorbed metal cations are used to characterize the metal sorbed at reactive surface sites. Two different systems are studied: (1) Hf(IV) sorbed onto the (001) basal plane of freshly cleaved mica and a surface oxidized silicon wafer and (2) U(VI) sorbed onto the (110) surface of α-Al2O3 at two different concentrations and two different orientations of the crystal surface plane to the polarization vector of the incident synchrotron radiation. Similar to findings reported for Hf(IV) sorbed onto amorphous silica, the EXAFS metrical parameters for Hf(IV) on both the mica (001) basal plane and on the oxidized silicon surface show that a mononuclear surface species forms. The cations are bound to silanol/aluminol groups present as defects on the mica surface in a fashion equivalent to binding to clay (hk0) edge sites. The polarization dependency of the XANES/EXAFS spectra of the α-Al2O3 surface sorbed U(VI) uranyl moiety shows that the linear uranyl cations exhibit a preferred orientation on the (110) surface. Comparison of the XANES spectral trends with data previously recorded for UO2(CH3CO2)2·2H2O single crystals and fits to the EXAFS data allows identification of the reactive sites as the AlO6 octahedral edges on the α-Al2O3 (110) surface.

An EXAFS spectroscopic, large-angle X-ray scattering, and crystallographic study of hexahydrated, dimethyl sulfoxide and pyridine 1-oxide hexasolvated mercury(II) ions

The structure of the solvated mercury(II) ion in water and dimethyl sulfoxide has been studied by means of large-angle X-ray scattering (LAXS) and extended X-ray absorption fine structure (EXAFS) techniques. The distribution of the Hg-O distances is unusually wide and asymmetric in both solvents. In aqueous solution, hexahydrated [Hg(OH(2))(6)](2+) ions in a distorted octahedral configuration, with the centroid of the Hg-O distance at 2.38(1) A, are surrounded by a diffuse second hydration sphere with HgO(II) distances of 4.20(2) A. In dimethyl sulfoxide, the six Hg-O and HgS distances of the hexasolvated [Hg{OS(CH(3))(2)}(6)](2+) complex are centered around 2.38(1) and 3.45(2) A, respectively. The crystal structure of hexakis(pyridine 1-oxide)mercury(II) perchlorate has been redetermined. The space group R(-)3 implies six equal Hg-O distances of 2.3416(7) A for the [Hg(ONC(5)H(5))(6)](2+) complex at 100 K. However, EXAFS studies of this compound, and of the solids hexaaquamercury(II) perchlorate and hexakis(dimethyl sulfoxide)mercury(II) trifluoromethanesulfonate, also with six equidistant Hg-O bonds according to crystallographic results, reveal in all cases strongly asymmetric Hg-O distance distributions. Vibronic coupling of valence states in a so-called pseudo-Jahn-Teller effect probably induces the distorted configurations.

Structure and bonding of bisaquamercury(II) and trisaquathallium(III) trifluoromethanesulfonate

The structure and bonding in bisaquamercury(II) trifluoromethanesulfonate, [Hg(OH2)2(CF3SO3)2]∞, and trisaquathallium(III) trifluoromethanesulfonate, [Tl(OH2)3(CF3SO3)3], have been studied by means of single-crystal X-ray diffraction, EXAFS and vibrational spectroscopy. The crystal structure of bisaquamercury(II) trifluoromethanesulfonate shows an unusual connectivity pattern. The mercury(II) ion strongly binds two water molecules axially with the Hg–O bond distance 2.11 A, and four oxygen atoms from four trifluoromethanesulfonate ions complete a tetragonally compressed octahedral coordination geometry, at the mean Hg–O distance 2.53 A. Two trifluoromethanesulfonate ions form double bridges between the bisaquamercury(II) entities giving rise to infinite >Hg(OH2)2 Hg(OH2)2< chains. The parallel chains are held together in layers by relatively strong hydrogen bonds with O(–H)⋯O distances in the range 2.688(9)–2.735(9) A. The O–D stretching vibrational frequencies of the hydrogen bonds in the partly deuterated compound occur in a broad band at about 2400 cm−1, bandwidth ca. 170 cm−1. The layers are connected only via van der Waals interactions between the protruding CF3 groups, consistent with the fragile sheet-like structure of the crystalline compound. Trisaquathallium(III) trifluoromethanesulfonate crystallises as molecular complexes where each thallium(III) ion binds three water molecules and three oxygen atoms from trifluoromethanesulfonate ions, with Tl–O bond distances in the range 2.18–2.24 A. A hydrogen bond network between the water molecules and trifluoromethanesulfonate ions with O(–H)⋯O distances in the range 2.65(1)–2.80(1) A holds the structure together. Raman and infrared spectra have been recorded and analysed. The changes in force constants and vibrational frequencies have been correlated with bond lengths for the S–O bond in the coordinated trifluoromethanesulfonate ion and for the Hg–O and Tl–O bonds, also including the hexaaquaions in the comparisons.

Complexation of Cm(III) with Fluoride in Aqueous Solution in the Temperature Range from 20 to 90 °C. A Joint TRLFS and Quantum Chemical Study

The formation of hydrated CmF2+ and CmF2+ species in aqueous solutions are studied in the temperature range of 20−90 °C at different fluoride concentrations and at constant ionic strength as well as at constant fluoride concentration and different ionic strengths by means of time-resolved laser fluorescence spectroscopy (TRLFS). The molar fractions of the Cm3+ aqua ion, CmF2+, and CmF2+ species are determined by peak deconvolution of the emission spectra. An increase of the mono- and difluoro complexes is observed with increasing fluoride concentration and/or increasing temperature. Using the specific ion interaction theory (SIT), the thermodynamic stability constants log K10 (CmF2+) and log K20 (CmF2+) as well as the values of Δε1 and Δε2 are determined as a function of temperature. The log K10 values increase from 3.56 ± 0.07 to 3.98 ± 0.06 and the log K20 values increase from 2.20 ± 0.84 to 3.34 ± 0.21 with increasing temperature from 20 to 90 °C. The value of Δε1 determined at 25 °C is in good agreement with literature data and shows a negligible temperature dependency in the studied temperature range. The value of Δε2 also shows only a moderate variation in the studied temperature range. The thermodynamic standard state data (ΔrHm0, ΔrSm0, ΔrGm0) are determined from the temperature dependence of the equilibrium constants at Im = 0 using the integrated Van’t Hoff equation. The fluorescence lifetime of the 6D′7/2(Cm3+) state is found to be constant at 63 ± 5 μs with increasing fluoride concentration. A model based on density functional theory (DFT) calculations is introduced to account for the additional quenching occurring through the near second sphere waters in the [Cm(H2O)8F]2+(H2O)18 complex.

First structural characterization of Pa(IV) in aqueous solution and quantum chemical investigations of the tetravalent actinides up to Bk(IV): the evidence of a curium break

More than a century after its discovery the structure of the Pa(4+) ion in acidic aqueous solution has been investigated for the first time experimentally and by quantum chemistry. The combined results of EXAFS data and quantum chemically optimized structures suggest that the Pa(4+) aqua ion has an average of nine water molecules in its first hydration sphere at a mean Pa-O distance of 2.43 Å. The data available for the early tetravalent actinide (An) elements from Th(4+) to Bk(4+) show that the An-O bonds have a pronounced electrostatic character, with bond distances following the same monotonic decreasing trend as the An(4+) ionic radii, with a decrease of the hydration number from nine to eight for the heaviest ions Cm(4+) and Bk(4+). Being the first open-shell tetravalent actinide, Pa(4+) features a coordination chemistry very similar to its successors. The electronic configuration of all open-shell systems corresponds to occupation of the valence 5f orbitals, without contribution from the 6d orbitals. Our results thus demonstrate that Pa(iv) resembles its early actinide neighbors.

Comparative investigation of N donor ligand-lanthanide complexes from the metal and ligand point of view

N-donor ligands such as n-Pr-BTP (2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine) studied here preferentially bind An(III) over Ln(III) in liquid-liquid separation of trivalent ac-tinides from spent nuclear fuel. The chemical and physical processes responsible for this selectivity are not yet well understood. We present systematic comparative near-edge X-ray absorption structure (XANES) spectroscopy investigations at the Gd L3 edge of [GdBTP3](NO3)3, [Gd(BTP)3](OTf)3, Gd(NO3)3, Gd(OTf)3 and N K edge of [Gd(BTP)3](NO3)3, Gd(NO3)3 complexes. The pre-edge absorption resonance in Gd L3 edge high-energy resolution X-ray absorption near edge structure spectra (HR-XANES) is explained as arising from 2p3/2 → 4f/5d electronic transitions by calculations with the FEFF9.5 code. Experimental evidence is found for higher electronic density on Gd in [Gd(BTP)3](NO3)3 and [Gd(BTP)3](OTf)3 compared to Gd in Gd(NO3)3 and Gd(OTf)3, and on N in [Gd(BTP)3](NO3)3 compared to n-Pr-BTP. The origin of the pre-edge structure in the N K edge XANES is explained by density functional theory (DFT) with the ORCA code. Results at the N K edge suggest a change in ligand orbital occupancies and mixing upon complexation but further work is necessary to interpret observed spectral variations.

Erratum to: The Effect of Monovalent Electrolytes on the Deprotonation of MAl12 Keggin Ions

In the original publication of this paper, the affiliation of the third and the fourth author were interchanged. The correct affiliation for William H. Casey is: Department of Chemistry, University of California, Davis, CA, 95616, USA. The correct affiliation for Gerhard Furrer is: Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zurich, Universitatstrasse 8, 8092 Zurich, Switzerland. Remi Marsac has moved to Ecole Nationale Superieure de Chimie de Rennes, UMR CNRS 6226, 11 Allee de Beaulieu, F-35708 Rennes Cedex 7, France, as of 01.05.2015.