Isotropic Nuclear Resonance Shifts

Abstract

It is shown that isotropic (or average) nuclear resonance shifts for a nucleus in a paramagnetic molecule in solution, and in a polycrystalline solid, can be used to distinguish between Fermi contact and "pseudocontact" contributions to isotropic nuclear-hyperfine interactions. The pseudocontact interaction is that isotropic hyperfine coupling which arises from the combined effects of (electron-spin)-(nuclear-spin) coupling, (electron-orbit)-(nuclear-spin) coupling, and electron spin-orbit interaction. When the magnetic hyperfine interaction between the electronic moment and nuclea.r spin is approximated by a point dipolar interaction, and the isotropic hyperfine interaction is exclusively pseudocontact, then the isotropic nuclear shift in a polycrystalline solid exceeds the solution shift by the factor 3(gll +U)!(gll +2U) where gil and u are the spectroscopic splitting factors parallel and perpendicular to the molecular symmetry axis. Isotropic shifts due to the Fermi contact interaction are the same for both solid state and solution cases.

DFT investigation of the effect of spin-orbit coupling on the NMR shifts in paramagnetic solids

“…In doublet systems, term (h) in Table I is commonly referred to as the pseudocontact shift. It derives from the coupling between the non-relativistic dipolar component of the hyperfine tensor and the g-anisotropy due to spin-orbit coupling [15]. As the pseudo-contact term arises from the dipolar hyperfine interaction, it leads to a shift that depends on the spatial position and orientation of the magnetic moment of the unpaired-electron spin density relative to the nuclear magnetic moment of the OC.…”

“…Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful technique for analysing the local structure in paramagnetic solids, as the unpaired electrons of the TM ions induce a paramagnetic shift and shift anisotropy that provide detailed information concerning the structural and chemical environment of the NMR observed centre (OC) [9][10][11][12][13]. However, the interpretation of these spectra proves very challenging, as the presence of the paramagnetic centres results in multiple effects on the observed NMR lineshapes [14][15][16][17]. The through-bond transfer of unpaired-electron spin density onto the nuclear position of the OC induces a so-called Fermi contact shift, which is a direct measure of the electronic structure of the TM, the electronic spin transfer through the TM-O-OC bond and the degree of interaction between the relevant orbitals [18].…”

Communication: Paramagnetic NMR chemical shift in a spin state subject to zero-field splitting

“…We consider a molecule in the frozen nuclei approximation (also known as the "solid state limit" of NMR 7,8 ). Assuming that the zero-field splitting in the degenerate ground state is much smaller than the energy separating the ground state from excited states and assuming that these excited states are not thermally accessible, the shielding tensor σ can be a) Electronic mail: asoncini@unimelb.edu.au.…”

2β-Ethynyl-5β,17β-dihydroxy-3,4-bisnorandrostane 17-acetate

“…The structure determination of this new type of steroid was undertaken as part of a program carried out in our Institute to study the induced shift by lanthanides. In order to calculate the induced shift according to the McConnell & Robertson (1958) equation, it was necessary to know the precise geometry of the molecule. An ORTEP drawing (Johnson, 1965) is given in Fig.…”