NMR Crystallographic Journey from Light to Heavy Atoms of Mercury(II)-DOTAM Complexes and Extraction of Related Structural Parameters.

Complexes of macrocyclic ligands are routinely used as MRI contrast agents and radionuclide carriers for PET and SPECT diagnostics and radiotherapy. This study explores the structural and electronic environments of two materials containing [Hg(dotam)]2+ cations, using an integrated approach combining single-crystal X-ray diffraction (SC-XRD), multinuclear solid-state magnetic resonance (ssNMR) spectroscopy (13C, 15N, 199Hg), and relativistic density functional theory (DFT) calculations. SC-XRD revealed distinct coordination motifs, including octa- and heptacoordinated [Hg(dotam)]2+ cations. Scalar and spin-orbit relativistic DFT computations accurately reproduced 13C and 15N chemical shifts, with a root-mean-square deviation of ∼0.7 ppm for 13C and ∼4.8 ppm for 15N, highlighting the importance of relativistic heavy atom effects. For 199Hg NMR, relativistic cluster-based methods (ADF/ReSpect) outperformed nonrelativistic approaches. An empirical regression model (χ̅) linked 199Hg shifts to the coordination number (CN) and averaged donor electronegativity (χ̅) (R2 = 0.86), enabling rapid structural inference. The isotropic 199Hg shift correlates with the charge on the Hg atom, influencing the p-type frontier molecular orbitals and their paramagnetic contributions to NMR shielding. This work highlights the potential of 199Hg NMR as a structural descriptor and offers a strategy for NMR crystallography involving heavy elements with possible implications for catalysis, ionic liquids, and Hg-based pharmaceuticals.