Mercury: Inorganic & Coordination ChemistryBased in part on the article Mercury: Inorganic & Coordination Chemistry by Gregory J. Grant which appeared in the Encyclopedia of Inorganic Chemistry, First Edition .

Abstract

Mercury is one of the oldest known elements. The element exhibits surprisingly different chemistry from its congeners zinc and cadmium, and it is the only group 12 member without a known beneficial biological role. Unique properties associated with the element and its compounds have led to diverse applications. However, many of these are being phased out to minimize further increases in the environmental and atmospheric burden with this toxic heavy metal. Motivations to study the compounds and complexes of mercury include potential for discovery of novel properties such as high‐temperature superconductivity and improved understanding of its interactions in physiological systems. Valuable characterization of mercury‐containing compounds is possible with 199 Hg NMR techniques. Mercury is the only group 12 member to have a stable monovalent state. Observed primarily in the oldest known and most common of all metal polycations, Hg 2 2+ , this metal–metal bonded species readily disproportionates into Hg 2+ and Hg 0 . Mercury(I) compounds, typically, have a linear structure of type XHgHgX. Halides, oxy salts, oxides, and coordination compounds with oxygen and weakly basic nitrogen‐donor ligands are best known for Hg 2 2+ . The most prevalent ionization state of mercury, Hg 2+ , is a d 10 metal ion, which lacks strong coordination number and geometry preferences. As a result, structural characterization of its compounds by X‐ray crystallography is particularly critical. A wide range of halides, pseudohalides, and chalcogenides of Hg 2+ are known. The softness of Hg 2+ has led to an investigation of coordination, with a wide variety of sulfur ligands and physiological sulfur donors being assumed to be the most important. Mercury(II) typically has a stronger affinity for S‐, N‐, and P‐donors than any other divalent metal ion. However, Hg 2+ also has a tendency to undergo incredibly rapid ligand exchange. Recent studies have shown that sterically demanding multidentate ligand systems can suppress ligand exchange processes.