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Issue 16, 2020
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Direct magnetic-field dependence of NMR chemical shift

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Abstract

Nuclear shielding and chemical shift are considered independent of the magnetic-field strength. Ramsey proposed on theoretical grounds in 1970 that this may not be valid for heavy nuclei. Here we present experimental evidence for the direct field dependence of shielding, using 59Co shielding in Co(acac)3 [tris(acetylacetonate)cobalt(III)] as an example. We carry out NMR experiments in four field strengths for this low-spin diamagnetic Co(III) complex, which features a very large and negative nuclear shielding constant of the central Co nucleus. This is due to a magnetically accessible, low-energy eg ← t2g orbital excitation of the d6 system. The experiments result in temperature-dependent magnetic-field dependence of −5.7 to −5.2 ppb T−2 of the 59Co shielding constant, arising from the direct modification of the electron cloud of the complex by the field. First-principles multiconfigurational non-linear response theory calculations verify the sign and order of magnitude of the experimental results.

Graphical abstract: Direct magnetic-field dependence of NMR chemical shift

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Article information


Submitted
11 Mar 2020
Accepted
06 Apr 2020
First published
06 Apr 2020

This article is Open Access

Phys. Chem. Chem. Phys., 2020,22, 8485-8490
Article type
Paper

Direct magnetic-field dependence of NMR chemical shift

A. M. Kantola, P. Lantto, I. Heinmaa, J. Vaara and J. Jokisaari, Phys. Chem. Chem. Phys., 2020, 22, 8485
DOI: 10.1039/D0CP01372B

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