139La NMR Research Articles

Novel Contrast Agents for Magnetic Resonance Imaging. Synthesis and Characterization of the Ligand BOPTA and Its Ln(III) Complexes (Ln = Gd, La, Lu). X-ray Structure of Disodium (TPS-9-145337286-C-S)-[4-Carboxy-5,8,11-tris(carboxymethyl)-1-phenyl-2-oxa- 5,8,11-triazatridecan-13-oato(5-)]gadolinate(2-) in a Mixture with Its Enantiomer

The syntheses of the ligand BOPTA, (4-carboxy-5,8,1 l-tris(carboxymethyl)-l-pheny1-2-oxa-5,8,1 l-triazatridecan13-oic acid; benic acid) and its Gd(III), La(III), and Lu(1U) complexes are reported. Protonation constants for BOPTA have been determined by potentiometry, and the microscopic protonation sequence has been investigated by 'H NMR. The results obtained together with the value of the Gd-BOPTA2- stability constant (log KML = 22.59) show that the complexing properties of the ligand, in comparison with DTPA, are little affected by the presence of the benzyloxymethyl residue in the structure. The solid state structure of Gd-BOPTA disodium salt [C22H2&01 I (H~O)Gd]Na2~/2H20 was determined in a single-crystal X-ray diffraction study. The structure consists of [C22H2a3011(H20)Gdl2- anions, sodium cations, and water molecules; the space group is Pi (Z = 2), with a = 9.083(6) A, b = 9.469(2) A, c = 16.698(6) A, a = 102.22(3), = 92.48(4)', y = 102.26(3), V = 1366(1) A3, and d = 1.84 g/mL. The gadolinium ion adopts a nine-coordinate geometry, which is best described as a distorted tricapped trigonal prism. Eight coordinating sites are occupied by the ligand (three nitrogen atoms and five carboxylate oxygens), and the ninth site is occupied by the oxygen atom of a water molecule. Relaxation studies have shown that in solution also Gd-BOPTA2- has one water molecule directly coordinated to the metal ion. 139La NMR studies on the La-BOPTA2- complex have further supported the view that such complexes maintain in solution the same kind of coordination as found in the solid state for Gd-BOPTA disodium salt. I3C NMR spectra of the diamagnetic La- and Lu-BOPTA2- complexes at various temperatures are consistent with the presence of two couples of isomers interconverting through a dynamic process. Such a process has previously been reported for the parent Ln-DTPA2- complexes.

Oxygen diffusion in La 2CuO 4+ δ from 139La NMR-NQR relaxation

High temperature (T > 200K) 139La NMR relaxation rates in single crystals La 2CuO 4+δ at two measuring frequencies are compared with zero field NQR measurements in order to study the diffusion of the interstitial oxygen.

139La NMR-NQR study of the oxygen diffusion in La2−x Sr x CuO4+δ

High-temperature (T>200 K) 139La NMR relaxation rates in single crystals of La2CuO4+δ (δ∼0.015 and δ∼0.002) at two measuring frequencies are presented and compared with zero-field NQR data for a series of La2−xSrxCuO4+δ powder samples with 0≤x≤0.08 and 0<δ0.013. For δ≠0 an enhancement of the relaxation rate is observed which is related to the time dependence of the quadrupole interaction. Quantitative information on the oxygen diffusion is obtained from the analysis of the data with a simple diffusion model. The results are discussed in relation to the problem of macroscopic phase separation occurring for higher oxygen content.

A 139La and 17O nuclear magnetic resonance study of the nature of La(III) first coordination sphere in acetonitrile solutions of hydrated lanthanum nitrate

The nature of the first coordination sphere of the La(III) cation in acetonitrile solutions of La(NO3)3.6H2O was investigated by 139La and 17O NMR. All three nitrate anions are coordinated to La(III). There is a competition between water and acetonitrile molecules for the occupancy of the La(III) first coordination sphere. The 139La and 17O NMR results, obtained for various concentrations of La(NO3)3.6H2O, were quantitatively interpreted through a chemical equilibrium model. It was shown that the presence of only two La(III) species, {La(III) (NO3−)3} and {La(III) (NO3−)3.H2O}, in rapid exchange in solution could account for all the NMR results. The variation of the 139La and 17O NMR parameters (chemical shifts and relaxation rates) with the concentration of La(NO3)3.6H2O results from the population increase of the species {La(III) (NO3−)3.H2O}. The chemical exchange between free and coordinated water molecules is also fast on the 17O NMR time scale. The 17O NMR signal of water is considerably broadened when it coordinates to the La(III) cation. This broadening was attributed to both direct and indirect interactions between the two quadrupolar nuclei 17O and 139La. The direct interaction comes from an increase of the electric field gradient at the 17O nucleus when a water molecule coordinates to the La(III) cation. The indirect interaction results from an 17O–139La scalar coupling. The detailed analysis of the 17O NMR spectra also allowed the determination of the indirect coupling constant between coordinated 17OH2 and 139La(III), [Formula: see text]88 ± 13 Hz.

A 139La NMR study of the interactions between the La(III) cation and D-ribose in aqueous solution

The interactions of the La(III) cation with D-ribose and with D-arabinose in aqueous solution were investigated by 139La NMR spectroscopy. In the case of D-ribose, the formation of a La(III)-sugar complex was indicated by variations of the 139La chemical shift and linewidth with an increase of the sugar concentration in solution. In contrast, the complexation of La(III) by arabinose is very weak and almost undetectable by 139La NMR. On the basis of a 1:1 stoichiometry, the stability constant for the complex of La(III) with D-ribose was calculated from the observed 139La chemical shift values. A similar treatment was done for the viscosity corrected 139La linewidths using arabinose as an uninteractive reference. The stability constants, K, obtained independently from 139La chemical shifts and linewidths are in good agreement, 2.8 ± 0.5 and 2.2 ± 0.6 M−1 respectively at 299.0 ± 0.5 K. The thermodynamic parameters for the complexation of La(III) by D-ribose could also be obtained: ΔH0 = −12 ± 2 kJ mol−1, and ΔS0 = −31 ± 5 J K−1 mol−1. These values are in very good agreement with those obtained by calorimetric measurements.

Studies on Some Lanthanoid Complexes of Heterocyclic Ligands: Complexes of 2-Pyrazinecarboxamide with Hydrogen-Bonding

Abstract Lanthanoid complexes of 2-pyrazinecarboxamide (PYZA) of the composition, [LnCl3(pyza)3] (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Y), were synthesized and the structures of the isolated complexes studied by elemental analyses, molar conductance, magnetic susceptibility, electronic, FT-IR and multinuclear NMR spectral techniques. Presence of intra- and intermolecular hydrogen bonding in the non-complexed (free state) PYZA and intramolecular hydrogen bonding in the complexed ligand (Ln(III) complex) was indicated by the FT-IR spectra (solution and solid states). Non-coordination through the &amp;gt;C=O and –NH2 groups in the Ln(III) complexes was implied by the FT-IR (solution state) and 13C NMR spectra. The 139La NMR spectrum implied a predominantly ionic bond and low symmetry in the complexes. The hypersensitive band profile of the Nd(III) complex remained uneffected with respect to pH and temperature variations.

Characterization of the 2,2′-bipyridine chelates of lanthanum(III) in acetonitrile. A 1H, 13C, 17O, and 139La NMR study

We have investigated the reaction between La(NO3)3•6H2O and 2,2′-bipyridine (bipy) in acetonitrile by means of 139La, 17O, 13C, and 1H NMR spectroscopy. The 139La spectra show up to three different sites with variable intensities attributed to solvated La(III) ions and to two complex species with one or two bipy moieties in the La(III) coordination sphere. 17O NMR indicates that during the complexation reaction, the coordinated water is totally displaced from the coordination sphere whereas the nitrate groups remain coordinated. Proton NMR data confirm the water expulsion. In addition, the proton chemical shifts of bipy, in comparison with the 13C NMR data, clearly show an anisotropic shielding when two bipy are coordinated to La(III). Therefore, the two bipy molecules are in close proximity in the coordination sphere. From the NMR results it has been shown that, during the complexation process, five different La(III) species are formed: [La(NO3)3(CH3CN)4], [La(NO3)3(CH3CN)3(H2O)], [La(NO3)3(bipy)(CH3CN)2], [La(NO3)3(bipy)(CH3CN)-(H2O)], and [La(NO3)3(bipy)2]. Each La(III) complex has a coordination member of 10, with NO3− and bipy acting as chelating ligands. Furthermore, the structure of the La(NO3)3(bipy)2 complex in solution shows similarities with the solid state compound. Finally, comparisons are made with the La(III) complexes previously obtained with 1,10-phenanthroline.

Thermodynamic and NMR Studies on the Complexation of Lanthanoid(III) Ions with o-Phenylenediamine-N,N,N′,N′-tetraacetate in Aqueous Solutions

Abstract The complex formation of o-phenylenediamine-N,N,N′,N′-tetraacetate (PhDTA, H4L) with trivalent lanthanoid ions (M3+) in aqueous solutions has been studied at a temperature of 25.0 ± 0.2 °C and an ionic strength of 1.0 M in NaClO4 by potentiometry, calorimetry, and 1H and 139La NMR. The formation constant, KML, of 1 : 1 PhDTA complexes increases monotonically with the atomic number of the central metal ions (log KML = 11.39 for La, and 16.26 for Lu), showing the tetrad effect and a linear free energy relationship with the formation constant of CyDTA complexes. The change in entropy increases gradually with increasing atomic number, as is the case for EDTA. The large change in entropy ( ≈ 257–329 J K−1 mol−1) overweighs the endothermicity ( = 5.4–14.6 kJ mol−1) of the complexation. The NMR study indicated that the La–PhDTA complex has four acetate groups with an identical magnetic environment and a lanthanum nucleus with higher electric symmetry in comparison with the corresponding EDTA and CyDTA complexes.

Structures in solution and in the solid state of the complexes of lanthanum(III) with 1,10-phenanthroline. X-ray crystallographic and proton, carbon-13, oxygen-17 and lanthanum-139 solution NMR studies

The reaction between hexahydrated lanthanum(III) nitrate and 1,10-phenanthroline (phen) in acetonitrile solution was investigated by [sup 1]H, [sup 13]C, [sup 17]O, and [sup 139]La NMR spectroscopy. The crystal structure of trinitratobis(1,10-phenanthroline)lanthanum(III) (La-(NO[sub 3])[sub 3](C[sub 12]H[sub 8]N[sub 2])[sub 2]) was determined by X-ray diffraction as having a monoclinic lattice. In solution, [sup 139]La NMR spectra have shown up to three sites in slow exchange with variable intensities. They were attributed to solvated La(III) ions and to two complex species with one or two phen ligands in the La(III) coordination shell. A more complete structural analysis by [sup 17]O NMR spectroscopy indicated that during the course of the complexation by phen, coordinated water was totally expelled from the La(III) coordination sphere, whereas all three nitrate groups remained coordinated. Proton NMR data have confirmed the total displacement of water. In addition, the proton chemical shifts of phen, in comparison with the [sup 13]C NMR data, clearly showed an anisotropic shielding contribution when two phen ligands were coordinated to La(III). This indicates that the two phen molecules are in a close vicinity in the coordination sphere. From the NMR results, one can conclude that the structure in solution of the 2:1 complex, La(NO[sub 3])[sub more » 3](phen)[sub 2], is very similar to the solid-state one. From [sup 139]La NMR spectroscopy, the populations of the various La(III) species were obtained and the apparent formation constants were calculated. « less

NQR and NMR studies in superconducting La 2CuO 4+δ

In the superconducting La 2CuO 4+δ, Cu NQR signals were observed at around 33.1 and 36.0 MHz together with the antiferromagnetic Cu NMR signals similar to those in La 2CuO 4. The NQR intensity on oxygen-loaded samples increases with increasing the loaded contents, d, of oxygen. The nuclear spin relaxation time, T 1, of Cu NQR indicates that the paramagnetic phase is in the superconducting state. La NMR was also measured to study microscopically a phase separation and magnetic behaviors in oxygen-loaded La 2CuO 4+δ.

Solid-state 139La NMR investigation of lanthanum-exchanged Y zeolites

The line shape of solid-state 139La NMR spectra is sensitive to the local symmetry of the La ion sites: investigation of calcined La-exchanged Y zeolites reveals sharp and broad signals corresponding to La ions located in supercages and in small cages, respectively.

139La NMR and NQR study of the temperature dependent structure of La 2CuO 4+δ

NMR and NQR reveal substantial structural changes in the metallic phase of La 2CuO 4+δ which occur below 220 K. The oxygen octahedra in the metallic phase are not tilted at phase separation; upon cooling to 40 K considerable tilt has developed. The low temperature structure is highly disordered.

NQR and NMR studies in superconducting La 2CuO 4+d

In the superconducting La 2CuO 4+d, Cu NQR signals were observed at around 33.1 and 36.0 MHz together with the antiferromagnetic Cu NMR signals similar to those in La 2CuO 4. The NQR intensity on oxygen-loaded samples increases with increasing the loaded contents, d, of oxygen. The nuclear spin relaxation time, T 1, of Cu NQR indicates that the paramagnetic phase is in the superconducting state. La NMR was also measured to study microscopically a phase-separation and magnetic behaviors in oxygen-loaded La 2CuO 4+d.

A high-resolution NMR study of the lanthanum-silicon-aluminum-oxygen-nitrogen system

Hieh-resolution 27Al, 29Si, and 139La NMR spectra have been obtained from crystalline phases of the La-Si-Al-O-N system. These results have further defined the 29Si chemical shift ranges in mixed coordination tetrahedra (i.e., SiOxN4-x, 0 ≤ x ≤ 4) and enabled the cation's influence on the chemical shift in such units to be investigated for the first time. The ability to distinguish distinct local environments, despite overlap of the 29Si chemical shift ranges from different units, has allowed structural refinement of certain phases (e.g., La4Si2O7N2). The 27Al NMR spectrum of LaAlO3 shows appreciable intensity from transitions other than the 1/2↔−1/2, emphasing the difficulties of quantitatively interpreting NMR spectra of quadrupole nuclei. For the first time MAS is applied to 139La NMR and is shown to have some limited applicability to the study of ceramics. High-resolution multinuclear NMR is shown to be a powerful monitor of phase development and probe of compositional detail in complex ceramic phase mixtures. © 1989, American Chemical Society. All rights reserved.

Variable pressure spectrophotometric equilibrium and 139La NMR kinetic studies of lanthanum(III) ion complex formation with 2,6-dicarboxy-4-hydroxypyridine in aqueous solution

Determination des constantes de vitesse et des parametres d'activation pour la complexation de l'ion La(III) par l'hydroxy-«4» pyridinedicarboxylique-2,6 acide, par spectrometrie RMN 139 La

Characterization of the 18-crown-6-lanthanum(III) complex in methanol using 139La nuclear magnetic resonance

The complex formed between LaCl 3·7H 2O and the macrocyclic ligand 18-crown-6 (18C6) in methanol has been characterized by 139La NMR. Two sites in very slow exchange on the 139La NMR chemical shift time scale coexist in methanolic solutions: solvated and 1 : 1 complexed 139La III. Both chemical shift and relaxation rate data point to the participation of the chloride counteranion and of the crown ether in the first coordination sphere of lanthanum(III). The equilibrium constant of formation of the complex, determined from the populations of the two 139La NMR sites, is in excellent agreement with previously determined data from the literature.

139La NMR as a tool for kineic studies

AbstractThe application of 139La NMR to study the kinetics of substitution reactions is described. Rate constants associated with fast substitution reactions on La3+ complexes in the presence of excess of the aqua‐ion can be obtained by measuring the line widths of the corresponding signals. Measurements as a function of temperature allow the separation of the kinetic and quardrupolar relaxation effects. The rate of aquation of La(2,6‐dicarboxy‐4‐hydroxypyridine)+ was measured in aqueous solution. The dissociation rate constant and the activation parameters obtained for this process are k298r = 207 ± 51 s−1, ΔH = 38.3 ± 3.1 kJ mol−1 and ΔS = −72 ± 8 J K−1 mol−1. The spin–spin relaxation rates of the lanthanum(III) in the two environments are described by 1/T = 550 ± 83 s−1 and EA = 26.4 ± 5.8 kJ mol−1 for the aqua‐ion and by 1/T = (2.00 ± 0.08) × 104 s−1 and EB = 16.3 ± 1.6 kJ mol−1 for the mono‐complex.

139La NMR and quantitative FT-IR investigation of the interaction between Ln(III) ions and various anions in organic solvents

139La NMR and quantitative FT-IR investigation of the interaction between Ln(III) ions and various anions in organic solvents

Darstellung und lanthan-139-NMR-spektroskopische charakterisierung von tris(cyclopentadienyl)bis(cyclohexylisonitril)lanthan(III)

139La NMR spectroscopy turns out to be a useful technique for distinguishing complexes of the type (C 5H 5) 3 La …L n (L = nitrile; n = 1 or 2) in solution. Guided by this finding, the first bis-isocyanide adduct ( n = 2) of a (C 5H 5 3Ln complex could be prepared (Ln = La).

Lanthanum-139 nuclear magnetic resonance studies of polyaminocarboxylate-lanthanum complexes in aqueous solution

Several complexes of La(III) with aminocarboxylate and polyaminocarboxylate ligands in aqueous solution have been studied using 139La chemical-shift and linewidth measurements. The ligand-induced shifts of the 139La NMR resonance were found to depend, at least to first order, on additive substituent contributions, and were empirically related to the number and type of coordinated oxygen and nitrogen atoms. A previously proposed relationship between the number of coordinated carboxylate oxygen atoms and observed 139La shifts does not seem to hold for the polyaminocarboxylate complexes and we propose a new empirical relationship which allows an accurate prediction of the number and types of ligand donors in these systems. The 139La linewidths also provide qualitative information about the symmetry of each La 3+ chelate. The results show that 139La NMR can be a powerful technique for elucidating the structure and dynamics of lanthanide complexes in solution.