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Rationalization of anomalous pseudocontact shifts and their solvent dependence in a series of c3-symmetric lanthanide complexes.

Vonci, Michele and Mason, Kevin and Suturina, Elizaveta A. and Frawley, Andrew T. and Worswick, Steven G. and Kuprov, Ilya and Parker, David and 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). pp. 14166-14172.

Abstract

Bleaney’s long-standing theory of magnetic anisotropy has been employed with some success for many decades to explain paramagnetic NMR pseudocontact 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 pseudocontact chemical shift, is extremely sensitive to minimal structural changes in the first coordination sphere of L1. We show that DFT structural optimizations do not give accurate structural models, as assessed by the experimental chemical shifts, and thus we determine a magnetostructural correlation and employ this to evaluate the accurate solution structure for each [LnL1]. This approach allows us to explain the counterintuitive pseudocontact shift behavior, 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 and polarity.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1021/jacs.7b07094
Publisher statement:This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/jacs.7b07094
Date accepted:07 July 2017
Date deposited:20 October 2017
Date of first online publication:08 September 2017
Date first made open access:08 September 2018

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