A general procedure for the calculation of theoretical nuclear magnetic resonance second moments in dipolar solids; application to oxalic acid dihydrate (original) (raw)
Related papers
An efficient method for evaluating the effect of lattice vibrations on the NMR second moment
Journal of magnetic resonance, 1979
An improved algorithm for the evaluation of intra-and inter-molecular contributions to the NMR second moment is presented. The final expressions are given in terms of quadratic forms of the second moment tensor which depends on the equilibrium crystal structure as well as on parameters describing average atomic and molecular motion, assuming the latter to be expressible by the rigid body motion formalism. These parameters are readily available once the crystal structure of the compound considered has been determined by X-ray or neutron diffraction methods, and may serve for the evaluation of second moments of single-crystal as well as polycrystalline specimens. The use of the second moment tensor formulation considerably reduces the computational effort which is required by such calculations when the Van Vleck formula is being directly evaluated. An explicit introduction of crystal symmetry into the second moment tensor formalism, presented in this paper, further enhances the efficiency and ease of application of the proposed method.
Chemical Physics Letters, 1997
. The use of ab initio Hartree-Fock techniques for the calculation of H quadrupole coupling constants DQCCs in hydrogen bonded molecular crystals has been assessed for the a and b polymorphs of oxalic acid dihydrate. Results demonstrate the importance of considering the full periodic structure, rather than a single molecule or a small cluster of molecules. Intramolecular contributions to the DQCCs and contributions arising from the first shell of neighbouring molecules and from outer shells are quantified. The influence of the size of basis set on the calculated DQCCs is investigated; the 6-31G ) ) basis set is found to give good agreement with experiment. Correlations between the calculated DQCCs and geometrical parameters are investigated. q 1997 Elsevier Science B.V. 14 molecules 9-11 , showing that the EFG at the N nucleus is dominated by the intramolecular contribu-0009-2614r97r$17.00 q 1997 Elsevier Science B.V. All rights reserved.
Nuclear magnetic resonance methods for measuring dipolar couplings in rotating solids
Analytica Chimica Acta, 1993
The nuclear dipole-dipole coupling is a strong function of internuclear distance, and can therefore be used as a sensitive probe of local molecular structure. In most cases, however, the simultaneous presence of anisotropic chemical shielding and multiple dipolar interactions prevents isolation of the dipole coupling between individual spin pairs. Under these circumstances, it is customary to improve spectral resolution by employing magic angle spinning (hIAS) which preserves the isotropic part of the chemical shift interaction but partially or fully averages the desired dipolar interactions. This article reviews NMR methods designed to selectively restore and measure dipolar couplings between like (homonuclear) spins and unlike (heteronuclear) spins in rotating solids. Applications of these methodsrotational resonance (R'), rotational-echo double resonance (REDOR), transferred-echo double resonance (TEDOR), dipolar recovery at the magic angle (DRAMA), simple excitation for the dephasing of rotational-echo amplitudes (SEDRA), and &driven dipolar recoupling (RFDR)-to investigate the structure of biomolecules are presented.
Orientation of single crystals using linear approximations to NMR transits
Journal of Magnetic Resonance, 2005
We have derived analytical expressions for determining the orientation of high-symmetry single crystals from line-crossings in a single rotation plot. We demonstrate the utility of the method using the strontium-87 resonance in strontium nitrate. Employing our new method, which we call orientation of single crystals using linear approximations to NMR transits (OSCULANT), in combination with fourth-order perturbation theory, we obtain a highly accurate value for the quadrupole coupling constant, and an estimate for the chemical shielding anisotropy.
On the evaluation of molecular dipole moments from multipole refinement of X-ray diffraction data
Chemical Physics Letters, 1999
Lack of physical constraints in the purely mathematical multipole refinement model can lead to basis set oÕerlap errors in the evaluation of static molecular properties from X-ray diffraction data. For the molecular dipole moment, the error is large for several of the crystals tested in this study: DL-histidine, DL-proline, p-nitroaniline and p-amino-p X -nitrobiphenyl. Two restricted models are tested. In the first, atomic charges are constrained at k-refinement values, while in the second k X -values based on multipole refinements of theoretical ab-initio structure factors are used to reduce the flexibility of the model. Both models provide a more localized description of the pseudo atoms compared with an unrestricted refinement, but the k X -restricted model gives a more consistent representation of the molecular dipole moments and superior agreement with the theoretical deformation density for DL-histidine. q 1999 Elsevier Science B.V. All rights reserved.
Freezing of molecular rotation in a paramagnetic crystal studied by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">mml:mmultiscripts<mml:mi mathvariant="normal">P<mml:mprescripts /><mml:none />mml:mn31 NMR
Physical review, 2021
We present a detailed 31 P nuclear magnetic resonance (NMR) study of the molecular rotation in the compound [Cu(pz)2(2-HOpy)2](PF6)2, where pz = C4H4N2 and 2-HOpy = C5H4NHO. Here, a freezing of the PF6 rotation modes is revealed by several steplike increases of the temperaturedependent second spectral moment, with accompanying broad peaks of the longitudinal and transverse nuclear spin-relaxation rates. An analysis based on the Bloembergen-Purcell-Pound (BPP) theory quantifies the related activation energies as Ea/kB = 250 and 1400 K. Further, the anisotropy of the second spectral moment of the 31 P absorption line was calculated for the rigid lattice, as well as in the presence of several sets of PF6 reorientation modes, and is in excellent agreement with the experimental data. Whereas the anisotropy of the frequency shift and enhancement of nuclear spin-relaxation rates is driven by the molecular rotation with respect to the dipole fields stemming from the Cu ions, the second spectral moment is determined by the intramolecular interaction of nuclear 19 F and 31 P moments in the presence of the distinct rotation modes.