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. Mercury atoms react with cyanogen in excess argon at 4 K to give four major products. Shown is a CCSD plot of the occupied 6s σ‐bonding molecular orbital (HOMO‐1) for the single bond in the NCHg−HgCN product.