Mercury(II) cyanide
Mercury cyanide, also known as mercuric cyanide, is a poisonous compound of mercury and cyanide. It is an odorless, toxic white powder. It is highly soluble in polar solvents such as water, alcohol, and ammonia, slightly soluble in ether, and insoluble in benzene and other hydrophobic solvents.
Molecular and crystal structure
At ambient temperature and ambient pressure, Hg2 takes the form of tetragonal crystals. These crystals are composed of nearly linear Hg2 molecules with a C-Hg-C bond angle of 175.0° and an Hg-C-N bond angle of 177.0°. Raman spectra show that the molecules distort at higher pressures. Between 16-20 kbar, the structure undergoes a phase transition as the Hg center changes from 2- to 4-coordinate as the CN groups bind to neighboring Hg centers forming via Hg-N bonds. The coordination geometry thus changes from tetragonal to tetrahedral, forming a cubic crystal structure, analogous to the structure of Cd2. Due to the ambidentate nature of the CN ligands, this tetrahedral structure is distorted, but the distortion lessens with increasing pressure until the structure becomes nearly perfectly tetrahedral at >40 kbar.As in the solid state, in aqueous solution, Hg2 molecules are linear.
Synthesis
Mercuric cyanide is formed from aqueous hydrogen cyanide and mercuric oxide:Hg2 can also be prepared by mixing HgO with finely powdered Prussian blue. In addition, it can be produced by treating mercuric sulfate with potassium ferrocyanide in water:
Another method to generate mercuric cyanide is through the disproportionation of mercury derivatives. In these reactions, metallic mercury precipitates, and Hg2 remains in solution:
Reactions
It rapidly decomposes in acid to give off hydrogen cyanide. It is photosensitive, becoming darker in color.Mercury cyanide catalyzes the Koenigs–Knorr reaction for the synthesis of glycosides.
Cyanogen, 2, forms upon heating dry mercury cyanide, but the method is inferior to other routes:
It serves as a source of Hg2+ in its reaction with sodium tetracarbonylcobalt:
Coordination polymers can be synthesized from Hg2 building blocks. Large single crystals of 2] form upon treating CuCl2, the soft Lewis acid Hg2, and N,N,N',N'-tetramethylethylenediamine (TMEDA). The migration of two labile chloride ligands from harder Cu to softer Hg drives the formation of the crystal.