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Rationalization of anomalous pseudocontact shifts and their solvent dependence in a series of C3-symmetric lanthanide complexes

Rationalization of anomalous pseudocontact shifts and their solvent dependence in a series of C3-symmetric lanthanide complexes
Rationalization of anomalous pseudocontact shifts and their solvent dependence in a series of C3-symmetric lanthanide complexes
Bleaney’s long-standing theory of magnetic anisotropy has been employed with some success for many decades to explain paramagnetic NMR pseudo-contact shifts, and has been the subject of many subsequent approximations. Here, we present a detailed experimental and theoretical investigation accounting for the anomalous solvent dependence of NMR shifts for a series of lanthanide(III) complexes, namely [LnL1] (Ln = Eu, Tb, Dy, Ho, Er, Tm, and Yb; L1: 1,4,7-tris[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane), taking into account the effect of subtle ligand flexibility on the electronic structure. We show that the anisotropy of the room temperature magnetic susceptibility tensor, which in turn affects the sign and magnitude of the pseudo-contact chemical shift, is extremely sensitive to minimal structural changes in the first coordination sphere of L1. We show that DFT structural optimisations do not give accurate structural models, as assessed by the experimental chemical shifts, and thus we determine a magneto-structural correlation and employ this to evaluate the accurate solution structure for each [LnL1]. This approach allows us to explain the counter-intuitive pseudo-contact shift behaviour, as well as a striking solvent dependence. These results have important consequences for the analysis and design of novel magnetic resonance shift and optical emission probes that are sensitive to the local solution environment.
0002-7863
14166-14172
Vonci, Michele
d51e76b9-8190-49a3-8cc6-4fa1229aa329
Mason, Kevin
b44d68df-9067-4812-a742-ff17df162f4b
Suturina, Elizaveta
24dd007d-949a-4852-99d1-ea42b00103ef
Frawley, Andrew T.
b690a92a-146a-42d9-9991-2817b4fc3beb
Worswick, Steven, Graham
e3f70075-e4f7-4b56-a20a-dbcfcecc90e9
Kuprov, Ilya
bb07f28a-5038-4524-8146-e3fc8344c065
Parker, David
31bfb567-907a-4490-af57-411089ae0e73
McInnes, Eric J.L.
bba4b839-d79c-4561-b6e7-c002cc251ff4
Chilton, Nicholas F.
850941d1-c8bf-40fd-abaa-6a5467a0e549
Vonci, Michele
d51e76b9-8190-49a3-8cc6-4fa1229aa329
Mason, Kevin
b44d68df-9067-4812-a742-ff17df162f4b
Suturina, Elizaveta
24dd007d-949a-4852-99d1-ea42b00103ef
Frawley, Andrew T.
b690a92a-146a-42d9-9991-2817b4fc3beb
Worswick, Steven, Graham
e3f70075-e4f7-4b56-a20a-dbcfcecc90e9
Kuprov, Ilya
bb07f28a-5038-4524-8146-e3fc8344c065
Parker, David
31bfb567-907a-4490-af57-411089ae0e73
McInnes, Eric J.L.
bba4b839-d79c-4561-b6e7-c002cc251ff4
Chilton, Nicholas F.
850941d1-c8bf-40fd-abaa-6a5467a0e549

Vonci, Michele, Mason, Kevin, Suturina, Elizaveta, Frawley, Andrew T., Worswick, Steven, Graham, Kuprov, Ilya, Parker, David, McInnes, Eric J.L. and Chilton, Nicholas F. (2017) Rationalization of anomalous pseudocontact shifts and their solvent dependence in a series of C3-symmetric lanthanide complexes. Journal of the American Chemical Society, 139 (40), 14166-14172. (doi:10.1021/jacs.7b07094).

Record type: Article

Abstract

Bleaney’s long-standing theory of magnetic anisotropy has been employed with some success for many decades to explain paramagnetic NMR pseudo-contact shifts, and has been the subject of many subsequent approximations. Here, we present a detailed experimental and theoretical investigation accounting for the anomalous solvent dependence of NMR shifts for a series of lanthanide(III) complexes, namely [LnL1] (Ln = Eu, Tb, Dy, Ho, Er, Tm, and Yb; L1: 1,4,7-tris[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane), taking into account the effect of subtle ligand flexibility on the electronic structure. We show that the anisotropy of the room temperature magnetic susceptibility tensor, which in turn affects the sign and magnitude of the pseudo-contact chemical shift, is extremely sensitive to minimal structural changes in the first coordination sphere of L1. We show that DFT structural optimisations do not give accurate structural models, as assessed by the experimental chemical shifts, and thus we determine a magneto-structural correlation and employ this to evaluate the accurate solution structure for each [LnL1]. This approach allows us to explain the counter-intuitive pseudo-contact shift behaviour, as well as a striking solvent dependence. These results have important consequences for the analysis and design of novel magnetic resonance shift and optical emission probes that are sensitive to the local solution environment.

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Accepted/In Press date: 6 September 2017
e-pub ahead of print date: 8 September 2017
Published date: 11 October 2017

Identifiers

Local EPrints ID: 414681
URI: http://eprints.soton.ac.uk/id/eprint/414681
ISSN: 0002-7863
PURE UUID: b569b5b4-1095-4a17-bdd4-a29a90be6783
ORCID for Steven, Graham Worswick: ORCID iD orcid.org/0000-0002-5864-9684
ORCID for Ilya Kuprov: ORCID iD orcid.org/0000-0003-0430-2682

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Date deposited: 05 Oct 2017 16:31
Last modified: 15 Sep 2021 04:42

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Contributors

Author: Michele Vonci
Author: Kevin Mason
Author: Elizaveta Suturina
Author: Andrew T. Frawley
Author: Steven, Graham Worswick ORCID iD
Author: Ilya Kuprov ORCID iD
Author: David Parker
Author: Eric J.L. McInnes
Author: Nicholas F. Chilton

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