Studies of Successive Phase Transitions and Molecular Motions in [Mg(H2O)6][SiF6] by 1,2H and 19F NMR

1998 ◽  
Vol 53 (6-7) ◽  
pp. 453-458 ◽  
Author(s):  
Junko Kimura ◽  
Takeshi Fukase ◽  
Motohiro Mizuno ◽  
Masahiko Suhara
Keyword(s):  
Phase Transitions ◽  
Nmr Spectra ◽  
Quadrupole Coupling Constant ◽  
Coupling Constant ◽  
Molecular Motions ◽  
Exponential Factor ◽  
H Nmr ◽  
Quadrupole Coupling ◽  
Constant E ◽  
Successive Phase

Abstract The successive phase transitions of [Mg(H2O)6][SiF6] were studied by measuring 2H NMR spectra. The quadrupole coupling constant e2Qq/h and asymmetry parameter η changed drastically at each transition temperature. 1,2H and 19F NMR Tl were measured for this compound to study the relation between the molecular motions and the successive phase transitions. The activation energy Ea and the pre-exponential factor τ0 for the reorientation of [SiF6]2- were estimated as 28 kJmol-1 and 6.0 x 10-14 s, and those of the 180° flip of H2O as 33 kJmol-1 and 4.0x 10-14 s. These two motions occur rapidly even in phase V. For the reorientation of [Mg(H2O)6]2+ , Ea = 62 kJmol-1 and τ0 = 1.1 x 10-16 s were obtained from the simulation of 2H NMR spectra. The jump rate of this motion is of the order of 104 -106 s-1 in phase II. These results suggest that the successive phase transitions are closely related to the motion of [Mg(H2O)6]2+ .

scholarly journals High Resolution and Solid State NMR Investigations of Subvalent Gallium Compounds

1986 ◽  
Vol 41 (1-2) ◽  
pp. 315-318 ◽  
Author(s):  
Hubert Schmidbaur ◽  
Theodore Zafiropoulos ◽  
Wolfgang Bublak ◽  
Paul Burkert ◽  
Frank H. Köhler
Keyword(s):  
Solid State ◽  
Nmr Spectra ◽  
Quadrupole Coupling Constant ◽  
Coupling Constant ◽  
Gallium Atom ◽  
Line Shapes ◽  
Quadrupole Coupling ◽  
Structure Determinations ◽  
Constant E ◽  
Gallium Compounds

The 71Ga NMR spectra of Ga[GaX4] melts and of solutions in benzene and other hydrocarbons show discrete sharp GaI and broad GaIII resonances. In the light of recent structure determinations, the solution GaI signals must be attributed to bis(arene)Ga+ complexes in which the gallium atom is η6-bonded to the hydrocarbons. The low line widths and strong high field shifts are attributed to an almost spherical shielding of the metal nucleus by the 4 s2 electrons. Solid state 69Ga and 71Ga NMR spectra of Ga[GaCl4] crystalline powder show only Ga1 resonances. While the 71GaI line is rather narrow, the 69GaI line has a complex fine structure. Consistent with the crystal structure of Ga[GaCl4], the Ga1 ion is calculated to have a very low quadrupole coupling constant e2q Q/h = 1.7 ± 0.1 MHz and an asymmetry parameter η = 0.44. Experimental and simulated line shapes (using literature models) are in satisfactory agreement, implying that the 69Ga signal splitting is due to second order quadrupolar effects for the central m = + 1/2 ⇋ - 1/2 transition. The analogous splitting of the 71Ga NMR line is too small to be detected.

scholarly journals Two-Dimensional Nutation NQR Broad-Line Spectra in Oriented Samples

2006 ◽  
Vol 61 (9) ◽  
pp. 499-504 ◽  
Author(s):  
Nicolay Sinyavsky ◽  
Irina Korneva ◽  
Michał Ostafin ◽  
Bolesław Nogaj ◽  
Mariusz Maćkowiak
Keyword(s):  
Asymmetry Parameter ◽  
Disordered Systems ◽  
Quadrupole Coupling Constant ◽  
Two Dimensional ◽  
Coupling Constant ◽  
Nuclear Spins ◽  
Radio Frequency Field ◽  
Quadrupole Coupling ◽  
Oriented Samples ◽  
Constant E

The NQR nutation method to determine the electric field gradient asymmetry parameter η in systems, where the resonance line is so broad that the radio frequency field can excite only a portion of the nuclear spins, is presented. In this situation, the recently developed spectroscopic methods are not applicable. Two-dimensional nutation NQR spectra of oriented powders are calculated and used to determine η at particular frequencies along a broad NQR line. The proposed method is useful for single crystals, oriented powders, glasses, and disordered systems even for small values of the asymmetry parameter. Therefore it can be used to evaluate fluctuations in η and the quadrupole coupling constant e2qQ due to inhomogeneities. We demonstrate the application of this method to oriented chalcogenide semiconducting glasses.

Electric Quadrupole Moment of the 14N Nucleus Determined by ab initio Cl Calculation on NH3

1986 ◽  
Vol 41 (1-2) ◽  
pp. 163-165 ◽  
Author(s):  
Tae-Kyu Ha
Keyword(s):  
Electric Field Gradient ◽  
Ab Initio ◽  
Electric Quadrupole ◽  
Quadrupole Coupling Constant ◽  
Basis Set ◽  
Electric Quadrupole Moment ◽  
Coupling Constant ◽  
Hartree Fock ◽  
Quadrupole Coupling ◽  
Constant E

Based on the calculated electric field gradient (q) from ab initio Cl wavefunctions with largebasis set (including ƒ functions on N and d functions on H) and the experimental nuclearquadrupole coupling constant (e Q q) for nitrogen in NH3, an improved value o f the quadrupole moment of 14N is proposed as Q (14N ) = 2.08 x 10-26cm2. The value calculated using a wavefunctionnear the Hartree-Fock limit enlarged ≈ 10% by the Cl treatment.

Hydrogen Bond Studies

1977 ◽  
Vol 32 (2) ◽  
pp. 134-139 ◽  
Author(s):  
Bo Berglund ◽  
Jörgen Tegenfeldt
Keyword(s):  
Asymmetry Parameter ◽  
Room Temperature ◽  
Sodium Perchlorate ◽  
Quadrupole Coupling Constant ◽  
Water Molecules ◽  
Coupling Constant ◽  
Nmr Spectrum ◽  
Quadrupole Coupling ◽  
Constant E ◽  
The Difference

The quadrupole splittings in the deuterium NMR spectrum from single crystals of deuterated sodium Perchlorate monohydrate, NaClO4-D2O, have been measured at 25 °C and - 55 °C. At room temperature, the 180° flip frequency of the D2O molecules is large compared to the difference between the splittings for the two deuterons. The average quadrupole coupling constant (e2 q Q/h) and asymmetry parameter η are 134.1(4) kHz and 0.621(5), respectively. At -55 °C, the electric field gradient tensors for each of the two deuterons were observed corresponding to slowly flipping water molecules, and e2 qQ/h and η for the two deuterons are 231.5(6) and 226.7(6) kHz and 0.196(4) and 0.195(5), respectively. The results indicate that the hydrogen positions in NaClO4-H2O are dynamically disordered

scholarly journals Proton and Deuteron NMR Study on Single Crystals of Na2ZnCl4 · 3 H2O (Na2ZnCl4 · 3 D2O)

1973 ◽  
Vol 28 (12) ◽  
pp. 1919-1931
Author(s):  
Alarich Weiss ◽  
A. Wüst
Keyword(s):  
Principal Axis ◽  
Quadrupole Coupling Constant ◽  
Coupling Constant ◽  
Gradient Tensor ◽  
H Nmr ◽  
Nmr Study ◽  
Nuclear Quadrupole Coupling Constant ◽  
Quadrupole Coupling ◽  
Direction Cosines ◽  
Nuclear Quadrupole

Single crystal 1H- and 2H-XMR spectra of Na2ZnCl4 · 3 H2O and Xa2ZnCl4 · 3 D2O, respectively, were studied. The following results have been obtained: The positions of the hydrogens and deuterons are described in the space group C23v- P 31m with one formula unit in the unit cell. The point positions are: HI(DI) in 3m: x = 0.455 ± 4, y = 0, z = 0.556 ± 5; HII(DII) in 3m: x = 0.675 ± 4, y = 0, z = 0.466 ± 5. The angle H-O -H (D-O-D) is 107.0° and the H-H distance is 1.603 + 3 Å. Including dynamical corrections, the equilibrium positions are: HI(DI) : x = 0.459 ± 4, y - 0, z = 0.550 ± 5; HII(DII): x = 0.669 ± 4, y = 0, z = 0.464 ± 5. The H-H distance is then 1.537 ± 5 Å. From the 2H-NMR the nuclear quadrupole coupling constant of the deuterons is at T = 22 °C: e2qQ/h = 132.0 ± 1.0 kHz; η = 0.754 ± 5. The major principal axis of the electric field gradient tensor is perpendicular to the twofold axis of the molecule D2O. At T = -25 °C for the two deuteron atoms of one molecule D2O, the values (e2qQ/h)I = 239.7 ± 1.0 kHz; ηI = 0.118 ± 2; (e2qQ/h)II = 235.9 ± 1.0 kHz; ηII = 0.125 ± 2 have been found. Here the intermediate principal axis of the FGT is perpendicular to the H-O-H plane. The direction cosines of the FGTs have been determined. The activation energy for the flipping process was found to be 12.7 kcal. mol-1. The possible hydrogen bonds O-H…Cl are discussed.

The Temperature Dependence of 121,123Sb, 35Cl, 79,81Br and 127I NQR Spectra in Complexes Cs3Sb2X9 (X = Cl, Br, I)

2000 ◽  
Vol 55 (1-2) ◽  
pp. 134-138 ◽  
Author(s):  
L. A. Zemnukhova ◽  
S. I. Kuznetsov ◽  
G. A. Fedorishcheva ◽  
R. L. Davidovich
Keyword(s):  
Electric Field ◽  
Aqueous Solutions ◽  
Electric Field Gradient ◽  
Temperature Dependence ◽  
Quadrupole Coupling Constant ◽  
Coupling Constant ◽  
Quadrupole Transition ◽  
Quadrupole Coupling ◽  
Coeffi Cients ◽  
Constant E

The 123,123Sb, 35Cl, 79,81Br and 127I NQR Spectra of the complexes Cs3Sb2X9 (X = Cl, Br, I), prepared from CsX and SbX3 aqueous solutions, were studied at 77-400 K. Analysis of the^ temperature coeffi-cients of the quadrupole transition frequency (v), quadrupole coupling constant (e2Qqzz) and asymme-try parameter of the electric field gradient (η) was carried out.

ß-NMR Study of the Electric Field Gradient in the Metallic Intercalation Compound LiC6

1986 ◽  
Vol 41 (1-2) ◽  
pp. 109-112 ◽  
Author(s):  
P. Freiländer ◽  
P. Heitjans ◽  
H. Ackermann ◽  
B. Bader ◽  
G. Kiese ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Intercalation Compound ◽  
Quadrupole Coupling Constant ◽  
Layered Compound ◽  
Thermal Neutrons ◽  
Coupling Constant ◽  
Nmr Study ◽  
Nuclear Magnetic Resonance Spectra ◽  
Quadrupole Coupling ◽  
Constant E

In the layered compound LiC6polarized β-active 8Li probe nuclei were produced by captureof polarized thermal neutrons. Nuclear magnetic resonance spectra of 8Li were recorded via theβ-radiation asymmetry. The 8Li quadrupole coupling constant e2qQ/h , measured in the temperature range T = 5 . .. 500 K decreases with increasing 7 from 45.2(8) to 22.8(4) kHz.Anomalies in the overall temperature dependence are discussed in terms of phase transitionsproposed for LiC6.

79,81Br−127I−NQR, and Crystal Structure of Glycyl-l-alanine Hydrobromide Monohydrate and Hydroiodide Monohydrate

1989 ◽  
Vol 44 (7) ◽  
pp. 659-668 ◽  
Author(s):  
Armin Kehrer ◽  
Shi-qi Dou ◽  
Alarich Weiss
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Quadrupole Coupling Constant ◽  
Coupling Constant ◽  
Lattice Constants ◽  
Nuclear Quadrupole Coupling Constant ◽  
Quadrupole Coupling ◽  
Constant E ◽  
Nuclear Quadrupole

Abstract The crystal structures of glycyl-l-alanine hydrobromide monohydrate, 1, and glycyl-l-alanine hydroiodide monohydrate, 2, were determined and the temperature dependence of the 127I NQR frequencies was investigated in the temperature range 77 <̳T/K <̳ 370. The 127I NQR frequencies are strongly influenced by hydrogen bonds and this is proved by the frequency shift of the H ⇄ D exchange. By deuteration the nuclear quadrupole coupling constant e2 qQh−1(127I) of 2 is shifted downwards 2.72 MHz at room temperature. The title compounds are isotype, and at room temperature they crystallize monoclinic with the space group C22 − P21 with two molecules in the unit cell. The lattice constants for 1 are a = 1068.7 pm, b = 614.1 pm, c = 762.0 pm, and β= 108.55° and for 2 are a = 1093.3 pm, 6 = 637.1 pm, c = 770.9 pm, and β= 107.29°.

Theory of Nuclear Quadrupole Interactions in Solid Fluoromethanes with Implanted 19F* Nuclei. Coupling of HF* and Host Molecule

1996 ◽  
Vol 51 (5-6) ◽  
pp. 565-571
Author(s):  
G. Gowri ◽  
Tina Briere ◽  
Sudha Srinivas ◽  
Hwa-Suck Cho ◽  
T.P. Das ◽  
...  
Keyword(s):  
Quadrupole Coupling Constant ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Molecular Systems ◽  
Hartree Fock ◽  
Nuclear Quadrupole Interactions ◽  
Field Gradients ◽  
Quadrupole Coupling ◽  
Constant E ◽  
Total Energies

Abstract The Quadrupole Coupling Constant e2qQ and Asymmetry Parameter η of fluorine for fluorine-substitute methane compounds are calculated using the Hartree-Fock Roothaan procedure. Our results are compared with experimental data from measurements by the Time Differential Perturbed Angular Distribution (TDPAD) technique using excited 19F* (spin 5/2) nuclei. The theoretical e2qQ’s for the 19F* nuclei in the fluoromethanes are in good agreement with experimental results. For CH2F2 and CHClF2 molecules, where finite η are expected from symmetry considerations, our results for η are small, 0.12 and 0.05 respectively, in agreement with experimental observation. Besides the 19F* coupling constants associated with the C-F bonds in fluoromethanes, additional interesting NQI parameters, close to those in solid hydrogen fluoride, are observed in the TDPAD measurements. It is demonstrated through investigations of the total energies and electric field gradients that these additional NQI parameters for the fluoromethanes can be explained by a HF* molecule hydrogen-bonded through the hydrogen to a fluorine atom in the host molecular systems. This complexing of an ionic molecule to the host molecules in organic solids containing strongly electronegative atoms is expected to be a general feature in both implantation and conventional techniques.

Temperature Dependence of 14N NQR and Phase Transitions in KNO2 Powder

1996 ◽  
Vol 51 (5-6) ◽  
pp. 769-772 ◽  
Author(s):  
Hae Jin Kim ◽  
Kee Tae Han ◽  
Sung Ho Choh
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Asymmetry Parameter ◽  
Quadrupole Coupling Constant ◽  
Coupling Constant ◽  
Nuclear Quadrupole Coupling Constant ◽  
Quadrupole Coupling ◽  
Two Temperatures ◽  
Nuclear Quadrupole

Abstract The temperature dependence of 14N NQR, measured at 77 to 300 K, is in better agreement with the model proposed by Blinc et al. than the Bayer theory. The nuclear quadrupole coupling constant and asymmetry parameter show a discontinuity at about 160 K and 230 K, respectively. The linewidths are broadened at these temperatures up to 22 kHz and 18 kHz, respectively. These results indicate that KNO2 undergoes phase transitions at these two temperatures.

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