Mercurophilic Interactions

The widely confirmed abundance of aurophilic interactions in the structural chemistry of gold(I) compounds gives reason to scrutinize the evidence for analogous mercurophilic interactions in mercury(II) compounds more sporadically advanced in the literature. From the inventory of early observations and more recently accumulated data it appears that the equilibrium distances of intra- and intermolecular Hg-a- - -Hg contacts (ca. 3.5 Å) are generally much larger than those of Au-a- - -Au contacts (ca. 3.0 Å). There are very few estimations of the small energy contributions associated with the Hg-a- - -Hg contacts from experimental data, but quantum-chemical calculations have confirmed that these energies also are generally much lower than those for the Au-a- - -Au contacts. Notwithstanding, there are several special cases where particularly short Hg-a- - -Hg distances, or the preferred modes of associations of molecules into oligo- or polymeric arrays, do indicate significant attractive mercurophilic interactions. Photophysical phenomena also suggest that for several groups of oligomeric organomercury(II) compounds there is a much stronger Hg-Hg interaction in the excited state, with interesting consequences for the emissive properties. Interestingly, the most intriguing observations that suggest mercurophilic interactions, like the polymercuration of oxygen, nitrogen, and carbon, date back to the 19th century (Roucher in 1844, Millon in 1839, Sakurai in 1880, and Hofmann in 1900, respectively) and still call for a rationalization (Chemical Equation).