Mercury Cyanides and Isocyanides: NCHgCN and CNHgNC as well as NCHgHgCN and CNHgHgNC: Simple Molecules with Short, Strong Hg-Hg Bonds.

Mercury atoms, laser-ablated from an amalgam dental filling target, react with cyanogen in excess argon during condensation at 4 K to form two major products in the 2200 cyanide M-C-N stretching region of the IR spectrum, which were assigned to NCHgCN and NCHgHgCN from their antisymmetric C-N stretching mode absorptions at 2213.8 and 2180.1 cm-1 . Two broader bands in the isocyanide region at 2098.2 and 2089.6 cm-1 were assigned to CNHgNC and CNHgHgNC. The N-bonded isomers were computed to be 603/33 and 823/69 times more intense IR absorbers than the C-bonded isomers at the CCSD level of theory. The dissociation energy for the NCHg-HgCN molecule into two HgCN molecules was calculated to be 296 kJ mol-1 and that for CNHg-HgNC into two HgNC molecules is 304 kJ mol-1 . These simple molecules with two cyanide or two isocyanide ligands have two of the shortest and strongest known Hg-Hg single bonds as the two electronegative CN ligands withdraw antibonding electron density from the bonding region.