Quadrupole Interaction Parameters Research Articles

Ionic conduction and 27Al MAS/NMR of B-site Al ion substitutions in La 4/3− yLi 3 yTi 2O 6

The 27Al MAS/NMR spectra of La 4/3− y Li 3 y Ti 2− x Al 4 x/3 O 6 ( y = 0.21, x = 0.01–0.60) were studied by the Massiot fitting program. The result shows a single signal Q1 produced by the second-order quadrupole interaction in low concentrations of x = 0.01–0.28. But in the high concentrations of x = 0.30–0.60, there are two components Q1 and a small and narrow component Q2 obtained. The quadrupole interaction parameters η Q and ν Q were estimated. We firstly found that the quadrupole interaction parameters η Q and ν Q were correlated with La 3+ occupation, lattice parameters and Al 3+ position and affected the ionic conductivity in the materials.

Electric field gradient at 99Ru nuclei in the series of intermetallic compounds Ce 1− xLa xRu 2 synthesized at high pressure

Parameters of the electric quadrupole interaction for the first excited state ( E=89.7 keV) of 99Ru nuclei for a number of the cubic Laves phase compounds Ce 1− x La x Ru 2, synthesized at high pressure, were determined by the perturbed angular γγ-correlation method. Compounds were synthesized at 8 GPa. It was revealed that the decrease of the average valence of a rare earth ion, caused by the substitution of La for Ce, results in the monotonous decrease of the quadrupole frequency ν Q from 43.3 MHz for CeRu 2 to 33.1 MHz for LaRu 2.

Hf3Al2 and Zr3Al2 Isostructural Aluminides Studied by PAC with 181Ta and 111Cd Probes

The electric quadrupole hyperfine interactions for 181Hf/181Ta and for 111In/111Cd probes in polycrystalline Zr3Al2 and Hf3Al2 compounds were measured in the temperature range 24–1100 K. The hyperfine quadrupole interaction parameters were determined after different doping techniques and heat treatments of the samples.181Hf/181Ta was found to substitute the Hf/Zr sites and the 111In/111Cd impurities appear to substitute both the 8(j) Al sites and the three nonequivalent Hf/Zr sites.

Quantum calculations of the electronic structure and NMR quadrupolar interaction parameters for tugtupite

Tugtupite [Na 8 (Al 2 Be 2 Si 8 O 24 )Cl 2 ] is an extremely ordered mineral containing 27 Al, 23 Na, and 9 Be quadrupolar nuclei. The quadrupolar interaction parameters (QI), C q and η, for these nuclei were calculated from the electronic structure by full-crystal linearized augmented plane-wave (FC LAPW) or ab initio molecular orbital (MO) calculations. The orientation of the EFG tensors, calculated using FC LAPW correspond with the crystallographic axes a1, a2, and c, and η at the Al site is equal to 0.00 as required by the symmetrical electron density distribution in the a-c planes. The electron density of states (DOS) shows the EFG to originate from the valence band of the p-p, p-s electrons. The agreement between the calculated QI values and experimental results for tugtupite shows that FC LAPW is very effective to evaluate the electronic structure of an ordered mineral, and aid in the interpretation of MAS NMR spectra. The combination of computational efficiency and accuracy of ab initio cluster MO calculations were examined by using different cluster sizes, basis sets, theoretical levels, and charge backgrounds using the Gaussian 98W program. A small cluster embedded in a point charge background gave sufficiently accurate 27 Al EFG tensors, with much greater computational efficiency than with WIEN2k. The MO cluster calculation became closer to the experimental results as the number of atoms in the clusters increased, but the calculation cost increased as well. The point-charge background was found to contribute about 10% to the EFG. MO calculations, with B3LYP level and basis set 6-311G+d** for the cluster of two atom shells around the central Al nucleus, gave quadrupole interaction values within 13% of that found by the FC LAPW method using the WIEN2k program. Therefore, MO cluster calculations can provide a more efficient but less accurate alternative to FC LAPW for quantum calculations of mineral structures.

Multinuclear ( 27Al, 29Si, 47,49Ti) solid-state NMR of titanium substituted zeolite USY

Multinuclear solid-state NMR spectroscopy, employing 29Si MAS, 27Al MAS/3Q-MAS and 47,49Ti wide-line experiments, has been used for the structural characterization of titanium substituted ultra-stable zeolite Y (Ti-USY). 27Al MAS experiments show the presence of aluminum in four (Al IV), five (Al V), and six (Al VI) coordination, whereas the multiplicity within Al IV and Al VI is revealed by 27Al 3Q-MAS experiments. Two different tetrahedral and octahedral Al environments are resolved and their isotropic chemical shifts ( δ CS) and second-order quadrupole interaction parameters ( P Q) have been determined by a graphical analysis of the 3Q-MAS spectra. The emergence of signal with higher intensity at –101 ppm in the 29Si MAS spectrum of Ti-USY samples indicates the possible occurrence of Q 4(3Si,1Ti) type silicon environments due to titanium substitution in the faujasite framework. High-field (11.74 T) operation, using a probehead specially designed to handle a large sample volume, has enabled the acquisition of 47,49Ti static spectra and identification of the titanium environment in the zeolite. The chemical shielding and electric field gradient tensors for the titanium environment in the zeolite have been determined by a computer simulation of the quadrupolar broadened static 47,49Ti NMR spectra.

Study of muon magnetic hyperfine and nuclear quadrupole interactions and easy axis in the organic ferromagnet p-Cl-Ph-CHN-TEMPO

The first-principles Hartree–Fock cluster procedure has been used for studying the electronic structure of the organic ferromagnetic p-Cl-Ph-CHN-TEMPO (4-(p-chlorobenzylideneamino)-2,2,6,6-tetramethylpiperidin-1-yloxyl) radical system with and without positive muon or muonium. Theory is able to provide quantitative information about the trapping sites for muon and muonium and the associated muon hyperfine interaction parameters. Using this information, two sites, one with muonium trapped near oxygen in the electronic singlet state of the muonium–radical pair system involved and the other with muon trapped near chlorine, are identified as likely candidates for the source of the experimentally observed μSR frequency of 3.2 MHz from zero-field measurement. The easy axis is obtained in both cases as the b-axis in the monoclinic lattice in agreement with the results of our magnetic dipole–dipole interaction studies using the magnetic moment distributions in the ferromagnetic state in the absence of muon and muonium. Nuclear quadrupole interaction parameters for nuclei adjacent to the trapped muon and muonium have been evaluated and their role in distinguishing between alternate trapping sites is discussed.

Hf and Zr aluminides with B f-type structure studied by PAC with 181Ta and 111Cd probes

The hyperfine quadrupole interaction parameters and their temperature dependences for 181Hf/ 181Ta and for 111In/ 111Cd probes in the polycrystalline HfAl and ZrAl isostructural compounds were determined. Strong preference of 111In solute for the Zr 2Al 3 phase occurring as a contamination fraction in ZrAl sample was observed.

Topotactic Transformations of Sodalite Cages: Synthesis and NMR Study of Mixed Salt‐Free and Salt‐Bearing Sodalites.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Analysis of correlation patterns in hyperfine sublevel correlation spectroscopy ofS=1/2,I=3/2 systems

The properties of two-dimensional four-pulse electron spin echo envelope modulation spectra of nuclei with nuclear spinI=3/2 in disordered systems are discussed by means of calculated lithium hyperfine sublevel correlation spectra. Since a case of small coupling is treated, the multifrequency transition components appear only in the first quadrant of the two-dimensional spectra. The influence of the hyperfine and nuclear quadrupole interaction parameters on the cross peak ridges in the two-dimensional powder pattern is analyzed. Furthermore the possibility to determine the magnitude of the dipolar hyperfine and the nuclear quadrupole coupling from the cross peak line shapes is investigated. In this context the potential of those spectral features representing the so-called multiquantum transitions for the interpretation of the spectra is demonstrated.

Reintroducing anisotropic interactions in magic-angle-spinning NMR of half-integer quadrupolar nuclei: 3D MQMAS.

Selective reintroduction of anisotropic interactions such as the chemical shift anisotropy (CSA) and homonucler dipolar (HMD) coupling were implemented in a high-resolution NMR spectroscopy for half-integer quadrupolar nuclei. Rotary resonance recoupling (R(3)) combined with the multiple-quantum magic-angle spinning (MQMAS) in a three-dimensional (3D) experiment provides not only site-specific high-resolution spectra to yield the quadrupolar interaction parameters but also the CSA or HMD interaction parameters. This 3D experiment provides an avenue for the complete local structural information of half-integer quadrupolar nuclei. Three-dimensional MQMAS experiments incorporating R(3) of HMD and CSA interactions were demonstrated on model compounds containing (11)B, (23)Na, and (87)Rb nuclei.

Theory of 14N and 17O Nuclear Quadrupole Interactions in the Single Amino Acids Occurring in the Protein Chain of Cytochrome c

The understanding of electron transport in proteins based on a novel technique involving muon spin rotation (μSR)measurements is a topic of great current interest. The technique, which involves study of spin relaxation of a positive muon (μ+) trapped in amino acids in protein chains due to the fluctuating magnetic field that the moving electron produces, is based on the premise that the electron is generated by ionization of a muonium (Mu) which was trapped at the same site as the μ+ left behind. In attempting to test this premise from first-principles for the Cytochrome c (Cyt c) system in which recent μSR measurements have been made, we have carried out Hartree- Fock investigations of the electronic structures of the bare amino acids and amino acids with + and Mu trapped at the oxygen of the C=O group common to all amino acids. With the aim that the comparison of theoretically predicted experimental nuclear quadrupole interaction (NQI) parameters will provide a useful test of the electron distribution in the amino acids of Cyt c, we present results for the nuclear quadrupole coupling constants (e2qQ) and asymmetry parameters (η) for the bare amino acids and the amino acids with trapped μ+ and Mu. The trends in 2 and for 14N and 17O between the various amino acids, as well as the changes in these parameters in the presence of μ+ and Mu are being analyzed. It would be helpful to have experimental data for e2qQ and to η compare with our predictions for the amino acids as they occur in vitro in polycrystalline Cyt c in which the SR measurements have been carried out. It is also hoped that the μSR technique will be able to provide experimental data on e2qQ and for the 14N and 17O nuclei to compare with our predictions

Temperature Dependence of 2H Nuclear Quadrupole Interaction in Very Short Hydrogen Bonds in Some Organic Acidic Salt Crystals

The 2H nuclear quadrupole interaction parameters, e2Qq/h and η, are closely related to the shape of the potential energy surface at hydrogen bonds and depend sensitively on their geometry. We measured the temperature dependence of the 2H NMR spectra of the crystalline acidic salts KDCO3, KD cetylenedicarboxylate, RbD acetylenedicarboxylate, and KD maleate, which contain very short O-D···O type hydrogen bonds. The temperature coefficient decreases with increase in the O···O distance in the hydrogen bond. Ab inito molecular orbital calculations of the electric field gradient tensor based on the temperature dependent structure of each crystal indicate that thermal expansion of the hydrogen bond geometry is not responsible for this tendency. Ab initio calculations also predict that a fictitious off center shift of the hydrogen position in a symmetric hydrogen bond causes very high e2 Qq/h values. This suggests that low energy vibrational excitation may be responsible for large positive d (e2 Qq/h)/dT values in symmetric hydrogen bonds.

Topotactic transformations of sodalite cages: synthesis and NMR study of mixed salt-free and salt-bearing sodalites.

A series of mixed sodalite samples, Na(8)[Al(6)Si(6)O(24)]Br(x).(H(3)O(2))(2-x), with the unit cell stoichiometries varying in the 0 < x <2 region, was made by hydrothermal synthesis and subsequently transformed into Na(6+x)[Al(6)Si(6)O(24)]Br(x).(4H(2)O)(2-x) and Na(6+x)[Al(6)Si(6)O(24)]Br(x).circle(2-x) sodalites. Here, circle refers to an empty sodalite cage. The three series, referred hereafter to as the Br/basic, Br/hydro, and Br/dry series, were characterized by powder diffraction X-ray and by (23)Na, (27)Al, and (81)Br magic angle spinning (MAS) NMR and high-resolution triple quantum (TQ) MAS NMR spectroscopy. We determined that incorporation of Br(-) anions is 130 times more preferred than incorporation of H(3)O(2)(-) anions during the formation of sodalite cages, which permitted precise control of the halide content in the solid. Monotonic trends in chemical shifts were observed as a function of cage occupancy, reflecting continuous changes in structural parameters. A linear correlation between (81)Br chemical shift and lattice constant with a slope of -86 ppm/A was observed for all three series. Likewise, (23)Na chemical shifts for Na(+) cations in salt-bearing sodalite cages correlate linearly with the lattice constant. Both results indicate a universal dependence of the (23)Na and (81)Br chemical shifts on the Na-Br distance. The (27)Al chemical shifts of Br/basic and Br/hydro sodalites obey an established relation between delta(cs) and the average T-O-T bond angle of 0.72 ppm/degrees. Br/dry sodalites show two aluminum resonances, characterized by significantly different chemical shifts and quadrupolar interaction parameters. In that series, local symmetry distortions are evident from strong quadrupolar perturbations in the NMR spectra. P(Q) values for (27)Al vary between 0.8 MHz in Br/basic sodalites and 4.4 MHz in the Br/dry series caused by deviations from the tetrahedral symmetry of the salt-free sodalite cages. For (23)Na, P(Q) values of 0.8, 0.8, 2.0, and 5.7 MHz were found for sodium in bromo, basic, hydro, and dry cages, respectively. In addition, both (23)Na and (81)Br spectra offer some evidence that the Br(-) anions in the Br/dry sodalite are displaced from the center of the expanded sodalite cage. For all three series, the spectral deconvolution of the (23)Na NMR line shapes permits an accurate determination of the mixed sodalite stoichiometry.

Time Differential Perturbed Angularγγ-Correlation Studies of Diethylenetriaminepentaacetic Acid Complexes with111In and111mCd

Static and dynamic electric quadrupole interactions of 1 1 1 Cd in complexes with diethylenetriaminepentaacetic acid were studied by the time differential perturbed angular γγ-correlation technique using two parent isotopes, 1 1 1 In(EC) 1 1 1 Cd and 1 1 1 m Cd. The measurements were carried out using neutral aqueous solutions of the diethylenetriaminepentaacetic-acid-complexes with initial isotopes at 293 K and 77 K. It was shown that the 1 1 1 Cd-diethylenetriaminepentaacetic-acid-complex in aqueous solutions at pH = 7.0 is characterised by the re-orientational correlation time of 7.7 x 10 - 1 1 s and an electric field gradient V z z = 6.7(2) × 10 2 1 V/m 2 with an asymmetry parameter η = 0.75(5). A direct comparison of the electric quadrupole interaction parameters for diethylenetriaminepentaacetic- acid-complexes with 1 1 1 In and 1 1 1 m Cd confirmed the proposal about the fragmentation of the complexes caused by the after-effects of electron capture in 1 1 1 In. An observed difference in the electric quadrupole interaction parameters obtained for the solutions with 1 1 1 In and 1 1 1 m Cd complexes reflects a process of a chemical rearrangement of the complex structure after the In decay into Cd.

Mössbauer spectra of 167Er and 166Er in pyrogermanate and diglycollate hosts

The hyperfine splittings and the Mössbauer spectra (MS) of the two isomers 166Er and 167Er in the pyrogermanate (or ErPG) and diglycollate (or ErDG) hosts were calculated using the values of the crystal field (CF) parameters and energy levels obtained previously from fitting the magnetic and optical results. The calculated thermal characteristics of the quadrupole interaction parameter P differed prominently for ErDG and ErPG in both the isomers, viz., for 166Er in ErDG the value of P increased from 1.5 to 21.3 MHz between 300 and 4 K, whereas in ErPG the corresponding change is insignificant ∼1 MHz. It was also found that the excited nuclear level of 166Er in both the compounds split into five doublets giving rise to a five finger pattern in the calculated MS as have been observed for Er 3+ in several other compounds. In case of the 167 isomer more complicated MS for ErDG and ErPG are expected. Due to the non-zero value of the hyperfine constant B in case of ErPG the nuclear wave functions have mixed components of m I which affected the intensity of the spectra. The hyperfine magnetic fields H hf were calculated for both the compounds and were found to be nearly the same, being equal to 4.4±0.1 MG. The hyperfine specific heat C hf were calculated for 167Er in both hosts and was found that T 2 C hf attained constant values at millikelvin temperature. This study showed that MS and C hf of ErDG and ErPG are expected to be quite sensitively affected by the anomalous behaviours observed in these compounds at low temperatures.

Ferroelectric phase transitions in systems of axially symmetric dipolar particles in elongational flow

Effects of steady elongational flow on orientational phase transitions in systems of uniaxial, elongated particles with dipole moments are considered. The Onsager model is used with mean-field dipole–dipole and excluded-volume quadrupole interactions, combined with quadrupole effects introduced by elongational flow. Self-consistent, equilibrium orientation distribution of dipole particles, equilibrium thermodynamic properties and phase transitions are controlled by three dimensionless parameters related to dipole–dipole interactions, excluded-volume effects and intensity of the flow field. Dipole and axial order parameters, phase equilibria, and phase instability points are discussed in the space of dipole and quadrupole interaction parameters. Apolar-to-polar phase transitions, as well as transitions between individual apolar phases are affected significantly by coupling between excluded-volume effects and elongational flow. Three ranges of flow intensity inducing different phase behaviour are discussed. In a the weak flow range, a single polar phase and two different apolar phases are predicted. Phase diagram shows a triple point and three equilibrium lines for different pairs of phases. In the medium flow range, the triple point disappears and phase diagram reduces to two phases, apolar and polar, with a single line of coexistence. The first-order apolar-to-polar phase transition appears at relatively low values of the quadrupole interaction parameter, while at higher values of the parameter, second-order transition takes place. The first-order ferroelectric transition, as well as the coexistence of apolar and polar phases, disappear at a critical flow intensity separating the range of medium and strong flow. Within the strong flow range, the ferroelectric transition is second-order in the entire range of quadrupole interactions. Dipole–dipole interactions, critical for the ferroelectric transition, are significantly reduced by flow potential, especially at stronger excluded-volume interactions. A critical flow intensity has been found at which ferroelectric transition is stabilised solely by the elongational flow. Above the critical flow intensity, the system exhibits single-phase behaviour with stable polar order. No elongational flow is capable to induce ferroelectric phase transition in systems with dipole interaction parameter lower than unity.

51V NMR Study of VOCl3Immobilized on the SiO2and MgCl2Surface

The magnetic shielding tensor and quadrupole interaction parameters, as well as the mutual orientation of tensors for the (≡SiO)VOCl2complex obtained by the immobilization of VOCl3on the SiO2surface are determined. The state of VOCl3on the surfaces of MgCl2and modified SiO2with all surface OH groups replaced by Cl atoms is studied. To prepare the modified SiO2, CCl4and SiCl4are used as chlorinating agents. The formation of structurally similar pentavalent vanadium complexes on the surface of these supports is shown. A model for the coordination environment of vanadium on the chlorine-containing supports is proposed. The vanadium atom exists in the distorted pentahedral environment and is bound to the support through either two chlorine atoms or chlorine and oxygen atoms. A correlation between the coordination of VOCl3and catalytic properties of VOCl3/MgCl2is assumed.

Measurement of Quadrupole Interactions in LaMO3 (M = Cr, Fe, Co) Perovskites by TDPAC

The perturbed angular correlation (PAC) technique has been used to study the electric field gradient (EFG) in LaCoO3 perovskite. The results are compared with those for LaCrO3, LaFeO3 measured earlier. The PAC probe, 111In → 111Cd, was introduced in the oxide lattice by means of chemical reaction during sample preparation. In the present work, the temperature dependence of the electric quadrupole interaction parameters, for LaCoO3 was investigated. The resulting systematics of EFG at 111Cd, in La(Cr,Fe,Co)O3 perovskites, reveals a linear dependence with temperature.

237 Np Mössbauer Investigations of (U 1-x Np x ) 2 Rh 2 Sn

Surprisingly, Np2Rh2Sn does not order magnetically whereas the uranium counterpart U2Rh2Sn orders antiferromagnetically at 24 K with a 5f moment μU≈0.38μB. We have investigated the magnetic and electronic properties of (U1−xNpx)2Rh2Sn solid solutions. For x=0.25 and 0.5, the ordering temperature decreases to 11 K whereas the Np-rich compound (x=0.75) shows the onset of magnetic order around T≈6 K. The average Np magnetic moment amounts to 0.84 μB,0.83μB and 0.25 μB respectively. The isomer shift slightly decreases, from −9.6 mm/s to −10.4 mm/s (versus NpAl2) as x increases. The values of the quadrupole interaction parameter in the ordered and paramagnetic state suggest that Np moments are parallel to c for x=0.25 and then rotate to the basal plane for higher x.

ESEEM studies of succinate:ubiquinone reductase from Paracoccus denitrificans.

Electron spin-echo envelope modulation (ESEEM) spectroscopy has been performed in order to obtain structural information about the environment of the reduced [2Fe-2S] cluster (S-1 center), the oxidized [3Fe-4S] cluster (S-3 center), and the flavin semiquinone radical in purified succinate:ubiquinone reductase from Paracoccus denitrificans. Spectral simulations of the ESEEM data from the reduced [2Fe-2S] yielded nuclear quadrupole interaction parameters that are indicative of peptide nitrogens. We also observed a weak interaction between the oxidized [3Fe-4S] cluster and a peptide 14N. There was no evidence for coordination of any of the Fe atoms to 14N atoms of imidazole rings. The ESEEM data from the flavin semiquinone radical were more complicated. Here, evidence was obtained for interactions between the unpaired electron and only the two nitrogen atoms in the flavin ring.