Multifrequency Nuclear Magnetic Resonance as an Efficient Tool To Investigate Heterospin Complexes in Solutions

Multifrequency Nuclear Magnetic Resonance as an Efficient Tool To Investigate Heterospin Complexes in Solutions Full article

Journal

Journal of Physical Chemistry A
ISSN: 1089-5639

Output data

Year: 2020, Volume: 124, Number: 7, Pages: 1343-1352 Pages count : 10 DOI: 10.1021/acs.jpca.9b11104

Authors

Fishman Natalya N. ¹ , Lukzen Nikita N. ¹ , Ivanov Konstantin L. ^1,2 , Edeleva Mariya, V ³ , Fokin Sergey, V ¹ , Romanenko Galina, V ¹ , Ovcharenko Victor, I ¹

Affiliations

1	(Данные Web of science) Russian Acad Sci, Siberian Branch, Int Tomog Ctr, Novosibirsk 630090, Russia
2	(Данные Web of science) Novosibirsk State Univ, Novosibirsk 630090, Russia
3	(Данные Web of science) Russian Acad Sci, Siberian Branch, Vorozhtsov Novosibirsk Inst Organ Chem, Novosibirsk 630090, Russia

We report a multifrequency nuclear magnetic resonance (NMR) study of heterospin complexes [Eu(SQ)(3)L-n], where SQ is 3,6-di(tert-butyl)-1,2-semiquinone, L is tetrahydrofuran (THF), pyridine (Py), or 2,2'-dipyridyl (Dipy), and n is the number of diamagnetic ligands. Multifrequency NMR experiments allowed us to determine the effective paramagnetic shifts of the ligands (L = THF or Py) and the chemical equilibrium constant for [Eu(SQ)(3)(THF)(2)]. In addition, we have found a strong magnetic field effect on the NMR line broadening, giving rise to very broad NMR lines at high magnetic fields. We attribute this effect to broadening under fast exchange conditions when the NMR spectrum represents a homogeneously broadened line with a width proportional to the square of the NMR frequency difference of the free and bound forms of L. Consequently, the line width strongly increases with the magnetic field. This broadening effect allows one to determine relevant kinetic parameters, i.e., the effective exchange time. The strong broadening effect allows one to exploit the [Eu(SQ)(3)(THF)(2)] complex as an efficient shift reagent, which not only shifts unwanted NMR signals but also broadens them, notably, in high-field NMR experiments. We have also found that [Eu(SQ)(3)Dipy] is a thermodynamically stable complex; hence, one can study [Eu(SQ)(3)Dipy] solutions without special precautions. We report an X-ray structure of the [Eu(SQ)(3)Dipy]center dot C6D6 crystals that have been grown directly in an NMR tube. This shows that multifrequency NMR investigations of heterospin compound solutions not only provide thermodynamic and kinetic data for heterospin species but also can be useful for the rational design of stable heterospin complexes and optimization of synthetic approaches.

Fishman N.N. , Lukzen N.N. , Ivanov K.L. , Edeleva M.V. , Fokin S.V. , Romanenko G.V. , Ovcharenko V.I.
Multifrequency Nuclear Magnetic Resonance as an Efficient Tool To Investigate Heterospin Complexes in Solutions
Journal of Physical Chemistry A. 2020. V.124. N7. P.1343-1352. DOI: 10.1021/acs.jpca.9b11104 WOS Scopus РИНЦ OpenAlex

Published online:	Jan 27, 2020
Published print:	Feb 20, 2020

Web of science:	WOS:000515216300015
Scopus:	2-s2.0-85080843313
Elibrary:	43255190
OpenAlex:	W3001741043

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