Paramagnetic NMR and EPR Spectroscopy of Transition Metal Complexes

Paramagnetic NMR and EPR spectroscopy together form a powerful toolkit for probing the electronic structure and dynamics of open-shell transition metal complexes. In paramagnetic NMR, unpaired electrons interact with nuclear spins via hyperfine couplings, giving rise to large, temperature-dependent shifts and enhanced relaxation rates. These effects—arising from Fermi-contact, spin-dipolar and spin-orbit mechanisms—provide unique insight into spin delocalisation pathways and local geometry. Meanwhile, EPR spectroscopy detects transitions between electron spin states in a magnetic field, yielding g-tensors, zero-field splitting parameters and hyperfine coupling constants that characterise the metal centre’s anisotropy, ligand field and covalency. Advances in quantum-chemical methods, including relativistic two- and four-component approaches, now enable quantitative prediction of these observables for complex systems. Combined NMR and EPR analyses have underpinned studies of catalytic active sites, molecular magnets and bioinorganic metalloenzymes, facilitating rational design of new materials and drugs. Recent progress in sensitivity, multiscale modelling and in operando measurements continues to broaden the scope of paramagnetic magnetic resonance in chemistry and biology.

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Paramagnetic NMR and EPR Spectroscopy of Transition Metal Complexes publication trend

The graph below shows the total number of articles in paramagnetic nmr and epr spectroscopy of transition metal complexes across all publications each year (not limited to Nature Index journals).

Technical terms

Paramagnetic NMR: Nuclear magnetic resonance of systems with unpaired electrons, where hyperfine interactions induce large shifts and relaxation enhancements.

EPR spectroscopy: Electron paramagnetic resonance technique that probes transitions between unpaired electron spin states to yield g-tensors, hyperfine couplings and zero-field splitting.

Hyperfine coupling: Interaction between nuclear and electron magnetic moments, comprising Fermi-contact, spin-dipolar and spin-orbit contributions.

Pseudocontact shift: Through-space NMR shift arising from magnetic anisotropy and dipolar interaction of unpaired electrons with nuclear spins.

g-tensor: Anisotropic factor describing how an electron’s magnetic moment responds to an external field, sensitive to ligand field and covalency.

References

1. Paramagnetic Effects in NMR Spectroscopy of Transition-Metal Complexes: Principles and Chemical Concepts. Accounts of Chemical Research (2024).
2. Nature of NMR Shifts in Paramagnetic Octahedral Ru(III) Complexes with Axial Pyridine-Based Ligands. Inorganic Chemistry (2023).
3. Decoding the Ambiguous Electron Paramagnetic Resonance Signals in the Lytic Polysaccharide Monooxygenase from Photorhabdus luminescens. Inorganic Chemistry (2022).