Probing mercury complex speciation with multinuclear NMR

Investigation of the solution-state coordination chemistry of mercury presents unique challenges. Multinuclear NMR methods are particularly appropriate for the characterization of mercury complexes in solution because ¹⁹⁹Hg has I∈=∈1/2 and a natural abundance of 16.85%. Although the coordination chemistry of Hg(II) with mono- and bidentate ligands is commonly plagued by rapid exchange processes, slow exchange conditions on the chemical-shift time scale have recently been identified for a variety of acyclic ligands with three or more donor groups and biological macromolecules. Heteronuclear coupling to ¹⁹⁹Hg has been detected over as many as five bonds in coordination compounds with multidentate ligands permitting characterization of the species prevalent under slow ligand exchange conditions. In spite of geometric isomerization processes, these studies have enhanced the ability to relate δ_Hg and J(¹⁹⁹Hg¹H) to structural trends.