Alarich Weiss

Correlations between 35Cl Nuclear Quadrupole Resonance (NQR) Frequencies of Chlorobenzene Derivatives and Characteristic Reaction Parameters of the Substituents

The 35Cl NQR frequencies (at 77°K) of a number of chlorobenzene derivatives have been measured. The frequencies (including additional data from the literature) have been correlated with characteristic parameters, such as Tafts σI and σR. It is found that the Bray–Barnes relation can be somewhat improved by introducing a parameter κ: ν = ν0 +  ∑ iκi. The following relations are found: (a) the effects of more than one substituent on the benzene are additive; (b) steric effects (o‐substituents) are not important for the NQR frequencies; (c) a correlation between the NQR frequency ν and Tafts σI and σR (correlation coefficient r = 0.976) shows the importance of the inductive effect on NQR. The mesomeric effect plays only a minor role in 35Cl NQR in benzene derivatives. Unknown σI values may be gained from NQR measurements; for the evaluation of σR, the determination of the chemical shift of 19F NMR seems to be the better method.

X-Ray, NMR, and NQR Investigations of the Crystal Structure and Charge Distribution of Sodium Tetrachloroaluminate, NaAlCl4

Abstract On single crystals of NaAlCl4 the NMR- and NQR-spectra of 23Na, 27Al, and 35Cl were studied at room temperature. The crystal structure of NaAlCl4 has been refined. A comparison of the NMR (NQR) data with the crystal structure data shows that the electric field gradients (EFG) at the chlorine sites are mainly determined by the partial covalency of the Al-Cl bond, whereas the EFG at the aluminum sites is determined by the small deviations of the AlCl4 ion from tetrahedral symmetry and by the influence of the lattice. ∣ e2 q Q/h ∣ (23Na) proves the dominant ionic character of sodium in the lattice. The experimental results for the crystal structure show minor deviations from Baenzigers data. The NMR (NQR) data at T=22 °C are [atom (∣e2 q Q/h ∣ / MHz; η)]: 23Na (1.1117±0.0012; 0.2153 + 0.0005); 27Al (1.4895±0.0012; 0.3375±0.0011) ; 35ClI (23.033±0.030; 0.182 ±0.025); 35ClII (22.520 ±0.010; 0.270 ± 0.005) ; 35ClIII (21.646 ±0.003; 0.315±0.007); 35ClIV (22.410±0.016; 0.197±0.010).

X-Ray Investigations of the Intermetallic Phases CaCd1-x Tlx and Caln1-x Tlx and Knight Shift Measurements of 205Tl- and 113Cd-NMR in the System CaCd1-x Tlx

The quasibinary systems CaCd1-xTlx and CaIn1-xTlx- form continuous series of solid solutions for all concentrations x: 0 ≦ x ≦ 1. All alloys of both systems crystallize with space group Oh1-PmSm and one formula unit per unit cell (CsCl-type structure). Considerable deviations from Vegard’s law occur for CaCd1-x Tlx, while they are negligible for CaIn1-x Tlx. No sign for the appearance of superstructures was found in either system after equilibrating them at 300 °C for two hours. In the system CaCd1-xTlx the Knight shift Ks of the 205Tl- and 113Cd-NMR was measured at room temperature as a function of x. Saturated Tl(CH3CO2)- and Cd(NO3)2 solutions served as reference samples. The Knight shift of the 205Tl-resonance increases remarkably with increasing concentration x, whereas the Knight shift of the 113Cd-NMR decreases slightly with increasing x. No simple qualitative explanation is found for Ks(Tl) =f(x) and Ks(Cd) =f(x)

Nuclear Quadrupole Resonance Study of 35Cl in Chloral Hydrate, CCl3CH(OH)2, and Chloral Deuterate, CCl3CH(OD)2

The nuclear quadrupole resonance (NQR) spectra of 35Cl in chloral hydrate and chloral deuterate were investigated in the temperature range between 77°K and 323 °K. Two modifications have been found for each substance. One of the modifications is unstable at room temperature and changes within a few weeks into the stable modification. The NQR spectrum can be explained in terms of crystal field effects.

ÜBER DEN EINFLUSS VON WASSERSTOFFBRÜCKENBINDUNGEN AUF EIN- UND ZWEIDIMENSIONALE INNERKRISTALLINE QUELLUNGSVORGÄNGE

Zusammenfassung Die Ausbildung von Wasserstoffbruckenbindungen kann bei nicht quellungsfahigen Verbindungen Ionenaustausch und Quellung ermoglichen und bei quellungsfahigen Verbindungen die Quellung uber die Einlagerung von zwei Flussigkeitsschichten hinaus fordern oder die Quellung begrenzen oder schlieslich die Quellung ganz verhindern. Bei der Desoxyribonucleinsaure fallt auf, das solche Kationen das Quellungsverhalten besonders deutlich beeinflussen, welche wegen ihrer Grose eventuell die Wasserstoffbruckenbindungen zwischen Pyrimidin- und Purinresten aufsprengen konnen. Diese gleichen Kationen konnen nach alteren Untersuchungen von R. Kuhn auch Mutationen bewirken.

EPR of Mn2+ in CdGa2S4 and in CdGa2Se4 ; Influence of Covalent Bonding on the Parameters of the Spin-Hamiltonian

Abstract The EPR-spectra of Mn2+ in CdGa2X4 (X = S, Se) single crystals were measured and described by a Spin-Hamiltonian with an axial and with a cubic crystal field component: D=-(225.3±0.2)·10-4 cm-1 and a= (6.6 ± 0.2)·10-4 cm-1 for CdGa2S4; D=-(919.3±0.3)·10-4 cm-1 and a= (15 ± 2)·10-4 cm-1 for CdGa2Se4. The g-values g∥ = 2.0012 ± 0.0005, g⊥ = 2.0016 ± 0.0010 for CdGa2S4 and g∥ = 2.0029 ± 0.0005, g⊥=2.0039 + 0.0010 for CdGa2Se4 are slightly different from those of the binary chalcogenides CdX (X = S, Se). The hyperfine constants A, - (64.0 ± 0.3)·10-4 cm-1 for CdGa2S4 and - (60.7 ±0.3)·10-4 cm-1 for CdGa2Se4 are nearly the same as those of the equivalent binary cadmium chalcogenides. It is shown that all parameters of the cadmium chalcogenides are characterized by the covalent part of the bonding. The g-values can be explained by an interaction of the 3d orbitals of Mn2+ with the ligand orbitals. The hyperfine constant is caused by an interaction of the excited 4s-Mn2+ states with the ligand states. By optical absorption measurements the value of the band gap in CdGa2X4 (X = S, Se, Te) is determined.

Band Structure of CaCd and CaTl and the Knight Shift of 113Cd- and 205Tl-NMR in the System CaCd1-x Tlx

The energy bands of ordered CaCd and CaTl have been calculated by the nonrelativistic augmented plane wave (APW) method. The electron structure in the system CaCd1-xTlx is deduced from these calculations by using the rigid band model for the phases with 0<x<1. The band structures of CaCd and CaTl are similar to the valence bands of other phases of the CsCl-type. From the energy eigenvalues the electronic density of states curve, the partial densities of states curves, and the Fermi energy have been obtained. For states near the Fermi surface the spin density at the position of the Cd- and Tl-nuclei has been determined. The Knight shift Ks of the 113Cd-NMR and the 205Tl-NMR in the system CaCd1-xTlx has been calculated as a function of x. The slope of the curve Ks (x) for the Cd-NMR is equal for experimental and theoretical results. The absolute value of the calculated Knight shift is about a factor of 1.4 too small. Only the direct term to the Knight shift has been calculated. Relativistic effects have been included by a scale factor. It has not been possible to explain the shape of the function (2) for the Tl-NMR, since a full relativistic APW calculation is necessary for CaTl

EPR of Mn2+ in Na2ZnCl4 · 3 H2O

The EPR spectrum of Mn2+ in Na,ZnCl4·3 H2O was investigated in the range 100 K ≦T≦300 K. The spectrum can be described by a Spin Hamiltonian with axial symmetry. The g factor is anisotropic, g∥ = 2.0007 ±0.0005; g⊥ = 2.0030 ± 0.0005. The axial crystal field splitting constants are D = (-901.0 ±2.0) -10-4 cm-1, B = (-5.7 ± 2.0) · 10-4 cm-1. The hyperfine splitting constants A = (-74.9 ±0.2)-10-4 cm-1 and A⊥ = (-74.2 ± 0.2) · 10-4 cm-1 have been determined. This corresponds to a Mn2+ ion bond to four Cl- ions within a tetrahedron. Since a large crystal field splitting constant D is observed, a strong axial crystal field at the site of the Mn2+ ion is assumed. From the temperature dependence of the crystal field splitting constant D a dominant phonon frequency of (117 ± 10) · 1011 sec-1 is deduced.

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

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.

127I Pure Quadrupole Resonance Spectrum of Orthoperiodic acid, H5IO6

The NQR-spectrum of 127I in orthoperiodic acid, Η5ΙΟ6 , has been studied on powder samples in the temperature range 77 Κ ≦ Τ ≦ 398 Κ. The resonance frequencies ν1 of the transition m(±3/2) ⇄ m (±1/2) are 45.248±0.005 MHz (77 K) and 44.976 ± 0.005 MHz (296 K). For the⇄ transition m(±5/2) ⇄ m(±3/2) the resonance frequencies v2 are 83.478±0.005 MHz (77 K) and 83.960 ± 0.005 MHz (296 K). The corresponding quadrupole coupling constants, e2 q Q/h, are 282.977±0.005 MHz (296 K), and 281.892±0.005 MHz (77 K). The asymmetry parameters η have been determined as 0.2372±0.0001 (296 K), and 0.2580±0.0001 (77 K). A small change of 0.4% for e2 qQ/h is accompanied by a rather large change of 21% for η within the temperature range investigated. e2 q Q/h=f(T) shows a maximum at ~ 313 K. No evidence of phase transition has been observed by NQR spectroscopy between 77 K and 398 K.