Temperature dependence of contact and dipolar NMR chemical shifts in paramagnetic molecules
Abstract
Using a recently proposed equation for NMR nuclear magnetic shielding for molecules with unpaired electrons [A. Soncini and W. Van den Heuvel, J. Chem. Phys. 138, 021103 (2013)], equations for the temperature (T) dependent isotropic shielding for multiplets with an effective spin S equal to 1/2, 1, 3/2, 2, and 5/2 in terms of electron paramagnetic resonance spin Hamiltonian parameters are derived and then expanded in powers of 1/T. One simplifying assumption used is that a matrix derived from the zerofield splitting (ZFS) tensor and the Zeeman coupling matrix (gtensor) share the same principal axis system. The influence of the rhombic ZFS parameter E is only investigated for S = 1. Expressions for paramagnetic contact shielding (from the isotropic part of the hyperfine coupling matrix) and pseudocontact or dipolar shielding (from the anisotropic part of the hyperfine coupling matrix) are considered separately. The leading order is always 1/T. A temperature dependence of the contact shielding as 1/T and of the dipolar shielding as 1/T{sup 2}, which is sometimes assumed in the assignment of paramagnetic chemical shifts, is shown to arise only if S ≥ 1 and zerofield splitting is appreciable, and only if the Zeeman coupling matrix is nearly isotropicmore »
 Authors:
 Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 142603000 (United States)
 Publication Date:
 OSTI Identifier:
 22416068
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Journal of Chemical Physics; Journal Volume: 142; Journal Issue: 5; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANISOTROPY; CHEMICAL SHIFT; COUPLING; ELECTRON SPIN RESONANCE; ELECTRONS; HAMILTONIANS; MAGNETIC SHIELDING; MOLECULES; MULTIPLETS; NUCLEAR MAGNETIC RESONANCE; PARAMAGNETISM; SPIN; TEMPERATURE DEPENDENCE; TENSORS; ZEEMAN EFFECT
Citation Formats
Martin, Bob, and Autschbach, Jochen, Email: jochena@buffalo.edu. Temperature dependence of contact and dipolar NMR chemical shifts in paramagnetic molecules. United States: N. p., 2015.
Web. doi:10.1063/1.4906318.
Martin, Bob, & Autschbach, Jochen, Email: jochena@buffalo.edu. Temperature dependence of contact and dipolar NMR chemical shifts in paramagnetic molecules. United States. doi:10.1063/1.4906318.
Martin, Bob, and Autschbach, Jochen, Email: jochena@buffalo.edu. 2015.
"Temperature dependence of contact and dipolar NMR chemical shifts in paramagnetic molecules". United States.
doi:10.1063/1.4906318.
@article{osti_22416068,
title = {Temperature dependence of contact and dipolar NMR chemical shifts in paramagnetic molecules},
author = {Martin, Bob and Autschbach, Jochen, Email: jochena@buffalo.edu},
abstractNote = {Using a recently proposed equation for NMR nuclear magnetic shielding for molecules with unpaired electrons [A. Soncini and W. Van den Heuvel, J. Chem. Phys. 138, 021103 (2013)], equations for the temperature (T) dependent isotropic shielding for multiplets with an effective spin S equal to 1/2, 1, 3/2, 2, and 5/2 in terms of electron paramagnetic resonance spin Hamiltonian parameters are derived and then expanded in powers of 1/T. One simplifying assumption used is that a matrix derived from the zerofield splitting (ZFS) tensor and the Zeeman coupling matrix (gtensor) share the same principal axis system. The influence of the rhombic ZFS parameter E is only investigated for S = 1. Expressions for paramagnetic contact shielding (from the isotropic part of the hyperfine coupling matrix) and pseudocontact or dipolar shielding (from the anisotropic part of the hyperfine coupling matrix) are considered separately. The leading order is always 1/T. A temperature dependence of the contact shielding as 1/T and of the dipolar shielding as 1/T{sup 2}, which is sometimes assumed in the assignment of paramagnetic chemical shifts, is shown to arise only if S ≥ 1 and zerofield splitting is appreciable, and only if the Zeeman coupling matrix is nearly isotropic (Δg = 0). In such situations, an assignment of contact versus dipolar shifts may be possible based only on linear and quadratic fits of measured variabletemperature chemical shifts versus 1/T. Numerical data are provided for nickelocene (S = 1). Even under the assumption of Δg = 0, a different leading order of contact and dipolar shifts in powers of 1/T is not obtained for S = 3/2. When Δg is not very small, dipolar and contact shifts both depend in leading order in 1/T in all cases, with sizable contributions in order 1/T{sup n} with n = 2 and higher.},
doi = {10.1063/1.4906318},
journal = {Journal of Chemical Physics},
number = 5,
volume = 142,
place = {United States},
year = 2015,
month = 2
}

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