NMR absolute shielding scales and nuclear magnetic dipole moments of transition metal nuclei

Abstract

This work reports new, accurate nuclear magnetic dipole moments for NMR-active transition metal nuclei where the long-standing systematic error due to obsolete diamagnetic correction has been eliminated by ab initio calculations of absolute NMR shielding constants. The error of the diamagnetic correction reaches ≈ −14 000 ppm for rhenium, which results in magnetic dipole moment corrections of about −3 × 10⁻²μ_N for the ¹⁸⁵Re and ¹⁸⁷Re nuclei. Such extreme values are one to two orders of magnitude larger than the corrections reported in the literature so far. These findings may help to resolve discrepancies in hyperfine splitting experiments involving rhenium ions. To obtain the corrected transition metal nuclear magnetic dipole moments, NMR shielding constants for a series of transition metal complexes defined as NMR standards [Harris et al., Pure Appl. Chem., 2001, 73, 1795] were calculated using the non-relativistic coupled cluster method and four-component relativistic density functional theory. To reproduce the experimental conditions of the NMR standards, the solvent effects were incorporated by explicit and implicit solvent models.