The pH dependence of Am(III) complexation with acetate: an EXAFS study

The complexation of acetate with Am(III) is studied as a function of the pH (1–6) by extended X‐ray absorption fine‐structure (EXAFS) spectroscopy. The molecular structure of the Am(III)–acetate complexes (coordination numbers, oxygen and carbon distances) is determined from the raw k³‐weighted Am L_III‐edge EXAFS spectra. The results show a continuous shift of Am(III) speciation with increasing pH value towards the complexed species. Furthermore, it is verified that acetate coordinates in a bidentate coordination mode to Am(III) (Am—C distance: 2.82 ± 0.03 Å). The EXAFS data are analyzed by iterative transformation factor analysis to further verify the chemical speciation, which is calculated on the basis of thermodynamic constants, and the used structural model. The experimental results are in very good agreement with the thermodynamic modelling.     

An EXAFS study of interionic distances in complex lanthanide oxides

When the smaller vanadium ion is substituted for niobium in NdNbO₄, the volume of the unit cell is almost unchanged; in the lanthanum and cerium counterparts the volume actually increases. In order to understand these phenomena we have employed the technique of extended x-ray absorption fine structure (EXAFS) to determine all of the near neighbor anion-cation distances in the series of mixed-B-ion oxides, NdNb_1?xV_xO₄, including the end-member compounds, NdNbO₄ and NdVO₄. We find that the average Nb-O, V-O and Nd-O interionic distances in the mixed compounds closely resemble the distances exhibited in the corresponding end-member compounds, but there are large variances associated with these averages. We take this to mean that, while crystal symmetry is not broken by the substitution of the smaller V⁵⁺ ion, there are substantial local distortions in bond lengths and angles in order to meet the ion-size requirements of immediate neighbors.     

(K,Mo)Y分子筛中钼组分的EXAFS研究

应用同步辐射Eextended X-ray Ab sorption Fine S tructure(EXAFS)技术研究固态法制备的KHMoY分子筛的氧化态和硫化态样品以及硫化态KHY／MoO3样品中钼组分的局域配位环境结构,并与KHMoY和KHY／MoO3 样品催化加氢活性结果进行对照。结果表明,随原子比（K＋2Mo）／Al的变化,钼原子周围的配位环境有显著的差异。当（K＋2Mo）／Al时,KHMoY和KHY/MoO3硫化后,钼组分主要以MoS2小原子簇分散在分子筛超笼中;（K＋2Mo)/Al>1时,钼组分则有两种存在环境,即分子筛超笼中的和分子筛外表的钼组分。分子筛超笼中的Mo S2原子簇的催化加氢合成醇选择性较高;分子筛外表面的MoS2微小颗粒的尺寸相对于超笼中的要大许多,其合成醇选择 性较低。     

Towards the origin of effective An(III)/Ln(III) separation by tridentate N-donor ligands: a theoretical study on atomic charges and polarisabilities for Cm(III)/Gd(III) separation

Soft N-donor ligand have shown to separate An(III) from Ln(III). The origin of the selectivity has not been entirely identified, and similar ligands show very different separation qualities. In this study we present a theoretical investigation of several relevant N-donor ligands in terms of atomic charges and polarisabilities obtained from an atoms in molecules approach. These allow new insights into the bonds between the ligands’ nitrogen atoms and the metal cation and explain a major part of the selectivity towards actinide ions. We deduct the superiority of 2,6-bis(1,2,4-triazine-3-yl)pyridines in separation quality compared to similar ligands for the Cm(III)/Gd(III) separation. Furthermore, improvements of existing ligands are developed that allow not only a direct experimental confirmation but also a systematic experimental study of the interactions and their influence on the selectivity.     

An X-ray photoelectron spectroscopic study of some bis(diamine)-copper (II) complexes

XPS data for a series of octahedral copper(II) diamine tetrafluoroborate and perchlorate complexes are interpreted in the following terms; (i) the inductive effect of diamine substituents; (ii) the degree of cation-anion interaction; (iii) the effect of progressive increase in diamine chelate ring size; and (iv) the Jahn-Teller effect in these complexes.     

121Sb Mössbauer spectroscopic study of a series of organoantimony(III) compounds

A systematic study of organoantimony(III) compounds, SbR₃, was attempted in view of the effect on Mössbauer parameters of the substituent on the aromatic ring. The Mössbauer parameters obtained in frozen organic solutions reflected the electronic effect caused by the characteristics of the substituents, electron donative or attractive, at the para position on the aromatic ring.     

An X-ray photoelectron spectroscopic study of some nickel (II) amine complexes

The X-ray photoelectron (XPS) spectra of several Ni(II) diamine complexes, a Ni(II) triamine complex and several Ni(II) diimine complexes are reported in terms of the Ni 2p, Cl 2p and N 1s core level binding energies. Theoretical models are presented to account for the quadratic relationship observed between XPS Ni 2p_{$\text{3}\text{2}$}binding energy shifts and the N-H infrared rocking frequency as related to these complexes. On the basis of this correlation, it is possible to discriminate between free counter-ions coordinated to the metal or involved in cluster-ion formation. Individual XPS data for these complexes are interpreted in terms of the intrinsic nature of the metal environment and an attempt is made to calculate the metal and donor nitrogen atomic charges for selected complexes.     

A spectroscopic study of uranium(VI) interaction with magnetite

The uranium sorbed onto commercial magnetite has been characterized by using two different spectroscopic techniques such as X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS). Magnetite samples have been put in contact with uranium(VI) solutions in conditions in which a high uranium uptake is expected. After several days, the magnetite surface has been analysed by XPS and EXAFS. The XPS results obtained are not conclusive regarding the uranium oxidation state in the magnetite surface. On the other hand, the results obtained with the EXAFS technique show that the uranium-magnetite sample spectrum has characteristics from both the UO₂ and schoepite spectra, e.g. a relatively high coordination number of equatorial oxygens and two axial oxygens, respectively. These results would indicate that the uranium sorbed onto magnetite would be a mixture of uranium(IV) and uranium(VI).     

Iron-57 mössbauer spectroscopic study of six-coordinate and seven-coordinate iron(III)-EDTA complexes

Newly prepared six-coordinate M[Fe(edta)] (M=Li, Na, K, Rb) and seven-coordinate H[Fe(edta)(H₂O)].H₂O were characterized by Mössbauer spectroscopy. The hygroscopic six-coordinate complexes were found to have high-spin Fe³⁺ ions in distorted octahedral sites.     

Synthesis and spectroscopic studies of iron (III) complex with a quinolone family member (pipemidic acid)

The interaction of iron (III) with pipemidic acid, Hpipem, afforded the complex [Fe (pipem) (HO)₂ (H₂O)]₂. The new complex has been characterised by elemental analyses, infra-red, EPR and XPS spectroscopies. The monoanion, pipem, exhibits O, O ligation through the carbonyl and carboxylato oxygen atoms. Six coordinate dimer distorted octahedral configuration has been proposed for [Fe (pipem) (HO)₂ (H₂O)]₂.     

Concentrated Fe(III)–nitrilotriacetate solutions: study by Raman spectroscopy and ab initio calculations

Fe(III)–nitrilotriacetate(NTA) aqueous solutions are used in various redox desulfurization processes. The nature of stable Fe–NTA complexes depends highly on parameters such as [Fe(III)] concentration, NTA/Fe ratio and pH value. These complexes can be characterized by potentiometric measurements or UV‐vis spectroscopy, but only at rather low concentrations. Using synthesis of solids, Raman spectra of these solids and ab initio calculations, a rational determination of the nature of complexes stable in water at high iron concentrations was proposed from the position sensitivity of the main low wavenumber band to the coordination sphere of iron cations. This band was assigned to ν(Fe N) stretching vibrations from ab initio calculations. Depending on the pH and NTA/Fe ratio of the prepared solutions, different species were identified from the Raman spectra. The present methodology can be extended to other metal–ligand systems to elucidate the nature of stable complexes in aqueous solution. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of paramagnetic doping on an inorganic polymer triaquadipotassiumbis(malonato)zincate: spectroscopic investigation

Spectroscopic investigations on Mn(II)-doped triaquadipotassiumbis(malonato)zincate [K₂(H₂O)₃] [Zn(mal)₂], an inorganic polymer, have been carried out at room temperature using single crystal electron paramagnetic resonance (EPR), ultraviolet–visible, FT-IR and powder XRD techniques. Single crystal rotations along the three orthogonal axes show more than 30 lines of patterns in EPR spectra, indicating the presence of two sites, one with a large D value and the other with a smaller D value. The calculated spin-Hamiltonian parameters are as follows. Site 1: g _xx =2.099, g _yy =2.092, g _zz =1.988, A _xx =9.77, A _yy =9.71, A _zz =8.96 mT, D _xx =?29.09, D _yy =?11.90, D _zz =40.99 mT; Site 2: g _xx =2.040, g _yy =1.995, g _zz =1.924, A _xx =9.51, A _yy =9.09, A _zz =8.80 mT, D _xx =?11.94, D _yy =?7.51 and D _zz =19.45 mT. The direction cosines of g/A/D do not match with the direction cosines of Zn–O bonds in the host lattice for either site, suggesting that both the Mn(II) sites entered the lattice interstitially. Optical results indicate a strong covalent bonding between the metal ion and ligands, with site symmetry being primarily octahedral. The FT-IR and powder XRD data confirm the retention of the crystal structure, even after incorporating a paramagnetic probe. Various admixture coefficients, bonding and optical parameters have also been calculated.     

Synthesis and spectroscopic properties of LiIn(WO4)2 nanopowders and single crystals doped with chromium(III) ions

LiIn(WO₄)₂ single crystals and nanopowders doped with chromium(III) ions were synthesized and investigated, including their EPR spectra and magnetic properties. The EPR spectra have shown low and high field lines attributed to isolated chromium ions with an electron spin S=3/2 and complex chromium centers with higher spin value, respectively. Magnetic susceptibility measurements revealed an almost linear dependence on the magnetic field. The electron resonance and magnetic properties have been related to the structural and spectroscopic data of the studied material.     

The electronic and magnetic properties of iron(III) derivatives of selected substituted meso-tetraphenyl porphyrins: ESR spectroscopic study

The electronic and magnetic behaviour of the nonsolvated ferric complexes of: (a) meso-tetratolyl-, (b) meso-tetra-4-hydroxyphenyl-, (c) meso-tetra-4-carboxyphenyl-, and (d) 5-(4-carboxyphenyl)-10,15,20-tritolyl-porphyrins was studied by ESR spectroscopy in the temperature range between 300 and 4 K. The complexes exhibit predominant contribution from the low-spin iron species at high temperature and a drastic shift toward the high-spin iron species at the low-temperature limit. These paramagnetic species are in different proportions at different temperatures, as well as in porphyrins with different substituents. The examined porphyrins obtained as disordered solids contain iron complexes with continuous short-range disorder which is additionally sensitive to change of temperature.     

The adsorption of acetylene on W(100) at room temperature: An electron spectroscopic study

The adsorption of acetylene on W(100) at room temperature has been studied by AES, ELS, thermal desorption, mass spectrometry, work function and LEED in one vacuum chamber. AES line profile analysis shows that there are at least two adsorption processes occurring at room temperature. Further, it is possible to explain all the AES results by assuming non-sequential adsorption into just two states, denoted by α and β. This picture was substantiated and embellished by comparison with other standard surface techniques. The α-state comprises either a C₂H₂ unit with an activation energy for desorption of $\text{2.3}\text{eV}\text{molecule}\text{(53}\text{kcal mole}{}^{\mathrm{?1}}\text{)}$ or CH units bounded through the carbon of the β-state. Saturation coverage for the α-state is 3 × 10¹⁴ molecules cm^?2. The β-state is dissociative at low acetylene exposures and comparison between a carbon covered surface and the β-state suggest the latter to be dissociative up to saturation. There also appears to be ca. 10¹⁴ hydrogen atoms cm^?2 on W(100) on room temperature acetylene saturation, the carbon content of the β-state being 9 × 10¹⁴ atoms cm^?2. The residual C?C bond from the molecule in the β-state remains unknown. No sign of ordering in the adsorbed species was detected, save the possibility of (1 × 1) in the β-state. Acetylene adsorption at 580 K showed hydrogen from the β-state to block acetylene adsorption by 15% at saturation. A two-site adsorption model for the β-state is proposed to explain the results. The α-state is bonded through the carbon of the β-state and it is speculated that the former adsorbs onto “β” domains where there is a critical minimum size for the latter.     

Theoretical study of Ir(III) complexes with cyclometalated alkenylquinoline ligands

Recently, it was reported that cyclometalated iridium(III) complexes of 2-((E)-2-phenyl-1-ethenyl)quinoline (PEQ) and 1-((E)-2-phenyl-1-ethenyl)isoquinoline (PEIQ) emitted saturated red light with high quantum efficiency and brightness. However, the energy difference between specific wavelengths due to the metal-to-ligand charge transfer (³MLCT) absorption and emission spectra showed rather large Stokes shifts, which originated at the predominant ³(π–π¹) ligand-based emission. In this paper, it is shown that these complexes are consistent with predominant ³(π–π¹) ligand-based emission. To develop the predominant ³MLCT emission of Ir complexes for a highly efficient phosphorescent complex suitable for red OLED devices, proper ligands having a highest occupied molecular orbital (HOMO) energy level similar to that of 2-phenylpyridine (ppy) ligand were designed to lead to strong mixing between π-orbitals of ligands and the 5d orbital of the centric iridium atom. In order to decrease the HOMO energy level and the lowest an occupied molecular orbital (LUMO) level simultaneously to maintain the same HOMO–LUMO energy gap, an electron accepting group such as F or CF₃ was introduced. By such manipulation of ligands in Ir complexes, it was theoretically possible to change the origin of emission in Ir complex from the predominant ligand-centered ³(π–π¹) excited state to the predominant ³MLCT excited state.