Norbert Weiden

A magnetic 4π goniometer for Zeeman-split NQR

Abstract With the aid of three mutually perpendicular Helmholtz coils a 4π Zeeman goniometer is constructed for application in NQR spectroscopy. Details of the construction are given. The spectrometer is cheked by measuring the zero splitting cone of 35 Cl NQR in a single crystal of NaClO 3 at room temperature. The precision of the goniometer is evaluated.

The C–Cl bonds in trichloroethylidene trichlorolactic ester, Cl3CCHOCOCHOCCl3. A 35Cl–NQR single crystal study

By single crystal 35Cl–NQR with a 4π Zeeman spectrometer, the six independent 35Cl‐nuclear quadrupole coupling tensors in trichloroethylidene trichlorolactic ester (chloralide) Cl3CCHOCOCHOCC13 have been studied at T=21 °C. The directions of the electric field gradient (EFG) tensor components have been determined. The main axes φzz are within ±0.5° parallel to the C–Cl bound directions. Very small asymmetry parameters in the range 0.005≤η≤0.053 are characteristic for the EFG tensors of Cl bond to carbon in aliphatic systems, and the six nuclear quadrupole coupling constants are found in the range 76.053≤e2qQh−1/MHz≤78.790. The orientations of the principal axes φxx and φyy is explained as due to intramolecular interactions likely of through space origin.

Crystal structure and C—Cl bond properties of 2,6-dichloroacetanilide, 2,6-Cl2C6H3NHCOCH3, phase I and phase II. An X-ray and 35Cl nuclear quadrupole resonance single-crystal study

The crystal structures of 2,6-dichloroacetanilide, 2,6-Cl2C6H3NHCOCH3, in the low-temperature phase II and high-temperature phase I have been determined at 295 K. [Phase II: C52h(P21/c); Z= 4; ρcalc= 1.475 Mg m–3; a= 783.4(2) pm, b= 1531.9(4) pm, c= 897.5(2) pm, β= 121.45(1)°; RW= 0.041. Phase I: D42(P212121); Z= 4; ρcalc= 1.416 Mg m–3; a= 1726.8(4) pm, b= 1167.4(3) pm, c= 474.9(2) pm; RW= 0.055.] The molecular geometry is very little influenced by the difference in packing between phase I and phase II. ν(35Cl)=f(T) was determined for both phases from 77 K up to the melting point/transition point. Single-crystal Zeeman split 35Cl n.q.r. investigations at T= 295 K revealed for (35Cl(2))II: e2ϕzzQh–1= 70.435(4)MHz; η= 0.1214(15); for (35Cl(6))II: e2ϕzzQh–1= 70.244(4)MHz; η= 0.1031(15); for (35Cl(2))I: e2ϕzzQh–1= 69.674(4)MHz; η= 0.1293(15); for (35Cl(6))I: e2ϕzzQh–1= 68.890(4)MHz; η= 0.1307(15). The principal axes ϕ(j)zz nearly coincide with the bond directions C(j)—Cl(j) in both phases. There is a small widening of the angle [ϕzz(35Cl(2)), ϕzz(35Cl(6))] in comparison with the value of the angle (C(2)—Cl(2), C(6)—Cl(6)) of the crystal structure. The influence of the —NHCOCH3 group on η and on the orientation of the axes ϕxx and ϕyy is discussed for both phases and is compared with the results reported for 2,3,6-Cl3C6H2OCOCH3.

Single crystal NQR and NMR study of (NH4)2InBr6·H2O

Abstract The 81 Br NQR tensors of (NH 4 ) 2 InBr 5 ·H 2 O have been studied on single crystals by combining a 4π Zeeman goniometer with Fourier transform NQR. AT T=293K the coupling constants are 136.27 e 2 φ ZZ Qh − (su81Br)/Mhz ≦ 146.14 and the asymmetry parameter 0.013 ≦ η ( 81 Br) ≦ 0.133. The EFG axes φ zz ( 81 Br) are almost parallel to the bond directions InBr. The strong changes of φ yy ( 115 In) and φ zz ( 115 In) with temperature can be explained by assuming small changes of the In(OH 2 ) bond distance in the complex anion (InBr 5 ·H 2 Cl 2⊝ . The D 2 O molecule within the deuterated complexes flips freely in the range studied (100 ≦ T/K ≦ 298). Small EFGs at the 14 N site in the cation ND ⊝ 4 are due to the EFG of the surrounding lattice charges.

A double resonance NQR experiment in Al2Br6

Abstract An NQR double resonance spectrometer is described. The spectrometer works in the range 0–10 MHz (lower channel) and 79–90 MHz (upper channel). Measurements of ¦e 2 qQ h ( 27 Al )¦ and η( 27 Al ) in Al2Br6 as a function of the temperature are reported together with the 79Br and 81Br NQR in this compound.

Molecular structure and nuclear quadrupole coupling tensors of 14N and 35Cl in 1‐chloro‐2,4‐dinitrobenzene. Phase I

The crystal structure of the orthorhombic, stable phase of 1‐chloro‐2,4‐dinitrobenzene was studied at T=295 K by x‐ray diffraction; space group D102h=Pccn; a=893.0(1) pm, b=1104.5(2) pm, c=1567.6(2) pm, Z=8, ρcalc=1.740 Mg m−3, all atoms in position 8(e). The Zeeman split single crystal 35Cl NQR gives e2ΦzzQh−1(35Cl)=74.287(4) MHz, η(35Cl)=0.1636(18) at T=295 K. At 110 K the values are: e2ΦzzQh−1(35Cl)=75.183(4) MHz, η(35Cl)=0.1572(20). Φzz(35Cl) is almost parallel to the bond C(1)–Cl(1) with a deviation of 2.8° from the bond direction. Φxx(35Cl) deviates from the normal to the ring plane by 9.9° and the deviation of Φyy(35Cl) from the ring plane amounts to 8.3°. By high field single crystal NMR the 14N nuclear quadrupole coupling tensors were determined. At T=295 K it is found: e2ΦzzQh−1 (14N(2))=0.9109(10) MHz, η(14N(2))=0.222(3); e2ΦzzQh−1 (14N(4))=1.0758(10) MHz, η(14N(4))=0.303(3). The (NO2)(2) group is twisted 41.9° against the ring plane whereas the group (NO2)(4) is much less twisted to the benzen...

23Na and 35Cl nuclear quadrupole interaction in Na2ZnCl4·3H2O. A single-crystal NMR study

Abstract The 35Cl and 23Na nuclear quadrupole interaction in single crystals of Na2ZnCl4·3H2O has been investigated at room temperature. With the high-field method (H0 ≈ 2·5 T) from the angular dependence of ν( 35 Cl ) (m = + 1 2 ⇌ m = − 1 2 ) and ν( 23 Na ) (m = ± 1 2 ⇌ ± 3 2 ) the coupling constant and η found are (number of positions; point symmetry; e2qQh−1/MHz; η; T (K)): 35ClI (1; 3m; 15.3676 ± 0.0010; 0.000 ± 0.002; 294); 35ClII (3; m; 18.308 ± 0.002; 0.0005 ± 0.0020; 294); 23Na (2; 3; 0.2617 ± 0.0003; 0.0000 ± 0.0005; 295.5). The direction cosines of the electric field gradient tensors were determined. The results are discussed with respect to possible hudrogenbonds Cl … HOH.

Investigation of alkali and 17O NQR spectra in chlorates and bromates by spin echo double resonance

Abstract The NQR spectra of 17 O (isotopic concentration 1%–5%) and of the alkali ions in NaBrO 3 , KBrO 3 , RbBrO 3 , CsBrO 3 , NaClO 3 , and KClO 3 , have been studied using the spin echo double resonance (SEDOR) method. In KBrO 3 the 39 K NQR frequency increases with increasing temperature in contrast to the NOR frequencies of the alkali nuclei in the five other substances. The values of e 2 qQh −1 ( 17 O) are slightly lower in the chlorates than in the bromates. For the bromates a linear relation between e 2 qQh −1 ( 17 O) and the electronegativity (and the ionic radius) of the alkali ions has been found.

Application of NQR double-resonance technique to a relative assignment of next-nearest neighbors within complex ions. Aluminum and bromine in KAl2Br7

Abstract The 1 r 6 dependence of the dipolar coupling can be used in the nuclear quadrupole double-resonance technique to gain information on relative positions of atoms within complex ions and molecules. With 27Al &.zharr; 81Br NQDR the terminal and bridging bromine atoms could be located relative to the two Al atoms for the anion [AI2Br7]⊖ in KAl1Br7. Application of the Townes-Dailey theory leads to a reasonable qualitative bond model for the ion IAl2Br7]⊖.

Molecular Motions in Solid [Sb(CH3)4]PF6. A Combined 11H,9F Nuclear Magnetic Resonance and Quasielastic Neutron Scattering Study

Abstract The molecular dynamics of tetramethylstibonium hexafluorophosphate, [Sb(CH3)4]PF6, is investigated over a broad temperature range. NMR spin lattice relaxation times T1 and the NMR second moments of the 1H and 19F nuclei were determined in the range 8.6 ≦ T/K ≦ 332.3 for polycrystalline [Sb(CH3)4]PF6. The complex cation undergoes isotropic tumbling for T > 260 K and thermally activated methyl group rotation in the temperature range T < 196 K. The activation energies for the transition from methyl group rotation to cation reorientation, as derived from NMR wideline (18.1 kJ/mol) and relaxation (22.7 kJ/mol) measurements, match. At very low temperatures pseudo classical line narrowing is observed, indicating tunneling motions of the methyl groups. The existence of two crystallographically inequivalent methyl groups is found by X-ray structure analysis at room temperature. The space group is P63mc, Z = 2; a = 738.6 pm, c = 1089.3 pm. It is confirmed by two steps in the temperature dependence of the signal intensity of the quasielastic line in neutron fixed window measurements in the temperature range 2 < T/K <148. The low temperature spin lattice relaxation times can be explained qualitatively by contributions of two crystallographically inequivalent methyl groups. Apparent activation energies for the two crystallographically different methyl groups are estimated. The complex anion undergoes isotropic tumbling in the temperature range 95 < T/K < 330. Above 330 K additionally translational motion is activated. Below 95 K the rotational motion of PF-6 is freezing in via an uniaxial state in range 40 < T/K <80. Activation energies for both isotropical tumbling (10.5 kJ/mol) and uniaxial rotation (5.8 kJ/mol) have been derived from 19F NMR spin lattice relaxation