Paramagnetic Effects in NMR Spectroscopy of Transition-Metal
Complexes: Principles and Chemical Concepts

J 2024

Paramagnetic Effects in NMR Spectroscopy of Transition-Metal Complexes: Principles and Chemical Concepts

NOVOTNÝ, Jan; Stanislav KOMOROVSKY a Radek MAREK

Základní údaje

Originální název

Paramagnetic Effects in NMR Spectroscopy of Transition-Metal Complexes: Principles and Chemical Concepts

Autoři

NOVOTNÝ, Jan; Stanislav KOMOROVSKY a Radek MAREK

Vydání

Accounts of Chemical Research, American Chemical Society, 2024, 0001-4842

Další údaje

Jazyk

angličtina

Typ výsledku

Článek v odborném periodiku

Obor

10400 1.4 Chemical sciences

Stát vydavatele

Spojené státy

Utajení

není předmětem státního či obchodního tajemství

Odkazy

DOI: 10.1021/acs.accounts.3c00786

Impakt faktor

Impact factor: 17.700

Kód RIV

RIV/00216224:14740/24:00139421

Organizační jednotka

Středoevropský technologický institut

DOI

https://doi.org/10.1021/acs.accounts.3c00786

UT WoS

001232029100001

EID Scopus

2-s2.0-85192078619

Klíčová slova anglicky

NMR spectroscopy;DFT calculations;hyperfine interaction;Fermi contact;paramagnetic spin-orbit;spin0-dipolar

Štítky

rivok

Příznaky

Mezinárodní význam, Recenzováno

Změněno: 9. 2. 2025 19:21, Mgr. Pavla Foltynová, Ph.D.

Anotace

V originále

Magnetic resonance techniques represent a fundamental class of spectroscopic methods used in physics, chemistry, biology, and medicine. Electron Paramagnetic Resonance (EPR) is an extremely powerful technique for characterizing systems with an open-shell electronic nature, whereas Nuclear Magnetic Resonance (NMR) has traditionally been used to investigate diamagnetic (closed-shell) systems. However, these two techniques are tightly connected by the electron–nucleus hyperfine interaction operating in paramagnetic (open-shell) systems. Hyperfine interaction of the nuclear spin with unpaired electron(s) induces large temperature-dependent shifts of nuclear resonance frequencies that are designated as hyperfine NMR shifts (deltaHF). Three fundamental physical mechanisms shape the total hyperfine interaction – Fermi-contact, paramagnetic spin-orbit, and spin-dipolar. The corresponding hyperfine NMR contributions can be interpreted in terms of through-bond and through-space effects. In this account, we provide an elemental theory behind the hyperfine interaction and NMR shifts and describe recent progress in understanding the structural and electronic principles underlying individual hyperfine terms. The Fermi-contact (FC) mechanism reflects the propagation of electron-spin density throughout the molecule and is proportional to the spin density at the nuclear position. As the imbalance in spin density can be thought of as originating at the paramagnetic metal center and being propagated to the observed nucleus via chemical bonds, the FC is an excellent indicator of the bond character. The paramagnetic spin-orbit (PSO) mechanism originates in the orbital current density generated by the spin-orbit coupling interaction at the metal center. The PSO mechanism of the ligand NMR shift then reflects the transmission of the spin polarization through bonds, similar to the FC mechanism, but it also makes a substantial through-space contribution in long-range situations. In contrast, the spin-dipolar (SD) mechanism is relatively unimportant at short-range, with significant spin polarization on the spectator atom. The PSO and SD mechanisms combine at long-range to form the so-called pseudocontact shift, traditionally used as a structural and dynamics probe in paramagnetic NMR (pNMR). Note that the PSO and SD terms both contribute to the isotropic NMR shift only at the relativistic spin-orbit level of theory. We demonstrate the advantages of calculating and analyzing the NMR shifts at relativistic two- and four-component levels of theory and present analytical tools and approaches based on perturbation theory. We show that paramagnetic NMR effects can be interpreted by spin-delocalization and spin-polarization mechanisms related to chemical bond concepts of electron conjugation in π-space and hyperconjugation in σ-space in the framework of Molecular Orbital (MO) theory. Further, we discuss the effects of environment (supramolecular interactions, solvent, crystal packing) and demonstrate applications of hyperfine shifts in determining the structure of paramagnetic Ru(III) compounds and their supramolecular host-guest complexes with macrocycles. In conclusion, we provide a short overview of possible pNMR applications in the analysis of spectra and electronic structure and perspectives in this field for a general chemical audience.

Návaznosti

GA21-06991S, projekt VaV

Název: Relativistické efekty v paramagnetické NMR spektroskopii (Akronym: RELMAG)

Investor: Grantová agentura ČR, Relativistické efekty v paramagnetické NMR spektroskopii

Přiložené soubory

ACR24_57_1467_acs.accounts.3c00786.pdf

Požádat o autorskou verzi souboru

Citovat

NOVOTNÝ, Jan; Stanislav KOMOROVSKY a Radek MAREK. Paramagnetic Effects in NMR Spectroscopy of Transition-Metal Complexes: Principles and Chemical Concepts. Accounts of Chemical Research. American Chemical Society, 2024, roč. 57, č. 10, s. 1467-1477. ISSN 0001-4842. Dostupné z: https://doi.org/10.1021/acs.accounts.3c00786.

@article{2399557,
   author = {Novotný, Jan and Komorovsky, Stanislav and Marek, Radek},
   article_number = {10},
   doi = {https://doi.org/10.1021/acs.accounts.3c00786},
   keywords = {NMR spectroscopy;DFT calculations;hyperfine interaction;Fermi contact;paramagnetic spin-orbit;spin0-dipolar},
   language = {eng},
   issn = {0001-4842},
   journal = {Accounts of Chemical Research},
   title = {Paramagnetic Effects in NMR Spectroscopy of Transition-Metal Complexes: Principles and Chemical Concepts},
   url = {https://pubs.acs.org/doi/10.1021/acs.accounts.3c00786},
   volume = {57},
   year = {2024}
}

TY  - JOUR
ID  - 2399557
AU  - Novotný, Jan - Komorovsky, Stanislav - Marek, Radek
PY  - 2024
TI  - Paramagnetic Effects in NMR Spectroscopy of Transition-Metal Complexes: Principles and Chemical Concepts
JF  - Accounts of Chemical Research
VL  - 57
IS  - 10
SP  - 1467-1477
EP  - 1467-1477
PB  - American Chemical Society
SN  - 00014842
KW  - NMR spectroscopy;DFT calculations;hyperfine interaction;Fermi contact;paramagnetic spin-orbit;spin0-dipolar
UR  - https://pubs.acs.org/doi/10.1021/acs.accounts.3c00786
N2  - Magnetic resonance techniques represent a fundamental class of spectroscopic methods used in physics, chemistry, biology, and medicine. Electron Paramagnetic Resonance (EPR) is an extremely powerful technique for characterizing systems with an open-shell electronic nature, whereas Nuclear Magnetic Resonance (NMR) has traditionally been used to investigate diamagnetic (closed-shell) systems. However, these two techniques are tightly connected by the electron–nucleus hyperfine interaction operating in paramagnetic (open-shell) systems. Hyperfine interaction of the nuclear spin with unpaired electron(s) induces large temperature-dependent shifts of nuclear resonance frequencies that are designated as hyperfine NMR shifts (deltaHF). Three fundamental physical mechanisms shape the total hyperfine interaction – Fermi-contact, paramagnetic spin-orbit, and spin-dipolar. The corresponding hyperfine NMR contributions can be interpreted in terms of through-bond and through-space effects. In this account, we provide an elemental theory behind the hyperfine interaction and NMR shifts and describe recent progress in understanding the structural and electronic principles underlying individual hyperfine terms. The Fermi-contact (FC) mechanism reflects the propagation of electron-spin density throughout the molecule and is proportional to the spin density at the nuclear position. As the imbalance in spin density can be thought of as originating at the paramagnetic metal center and being propagated to the observed nucleus via chemical bonds, the FC is an excellent indicator of the bond character. The paramagnetic spin-orbit (PSO) mechanism originates in the orbital current density generated by the spin-orbit coupling interaction at the metal center. The PSO mechanism of the ligand NMR shift then reflects the transmission of the spin polarization through bonds, similar to the FC mechanism, but it also makes a substantial through-space contribution in long-range situations. In contrast, the spin-dipolar (SD) mechanism is relatively unimportant at short-range, with significant spin polarization on the spectator atom. The PSO and SD mechanisms combine at long-range to form the so-called pseudocontact shift, traditionally used as a structural and dynamics probe in paramagnetic NMR (pNMR). Note that the PSO and SD terms both contribute to the isotropic NMR shift only at the relativistic spin-orbit level of theory. We demonstrate the advantages of calculating and analyzing the NMR shifts at relativistic two- and four-component levels of theory and present analytical tools and approaches based on perturbation theory. We show that paramagnetic NMR effects can be interpreted by spin-delocalization and spin-polarization mechanisms related to chemical bond concepts of electron conjugation in π-space and hyperconjugation in σ-space in the framework of Molecular Orbital (MO) theory. Further, we discuss the effects of environment (supramolecular interactions, solvent, crystal packing) and demonstrate applications of hyperfine shifts in determining the structure of paramagnetic Ru(III) compounds and their supramolecular host-guest complexes with macrocycles. In conclusion, we provide a short overview of possible pNMR applications in the analysis of spectra and electronic structure and perspectives in this field for a general chemical audience.
ER  -

NOVOTNÝ, Jan; Stanislav KOMOROVSKY a Radek MAREK. Paramagnetic Effects in NMR Spectroscopy of Transition-Metal Complexes: Principles and Chemical Concepts. \textit{Accounts of Chemical Research}. American Chemical Society, 2024, roč.~57, č.~10, s.~1467-1477. ISSN~0001-4842. Dostupné z: https://doi.org/10.1021/acs.accounts.3c00786.

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