The fine effects of high magnetic fields on hyperfine shifts

Abstract

We report a comprehensive investigation into the magnetic field dependence of NMR hyperfine shifts in paramagnetic systems, a critical observable in the study of molecular magnetism. By combining high-field NMR experiments with quantum chemical calculations, we demonstrate that hyperfine shifts exhibit a measurable dependence on the external field. This dependence arises from the interplay between partial molecular alignment and the nonlinear response of the induced magnetic field to the applied magnetic field. We consistently observe a systematic decrease in shifts at higher fields, indicating that the nonlinear contribution is the dominant mechanism. This effect is particularly strong in lanthanoid complexes, where the relative reduction of the shift is primarily determined by the central metal ion. For transition metals, the field dependence depends on the balance of contact and pseudocontact shifts, providing new constraints to check computational protocols.