At ambient temperature and ambient pressure, Hg(CN)2 takes the form of tetragonal crystals.[3] These crystals are composed of nearly linear Hg(CN)2molecules with a C-Hg-C bond angle of 175.0° and an Hg-C-N bond angle of 177.0° (Aylett[2] gives slightly different values of 189° and 175°, respectively). Raman spectra show that the molecules distort at higher pressures. Between 16-20 kbar, the structure undergoes a phase transition as the Hg(II) 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 Cd(CN)2. 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.[6]
As in the solid state, in aqueous solution, Hg(CN)2 molecules are linear.[2]
Synthesis
Mercuric cyanide is formed from aqueous hydrogen cyanide and mercuric oxide:[7]
Another method to generate mercuric cyanide is through the disproportionation of mercury(I) derivatives. In these reactions, metallic mercury precipitates, and Hg(CN)2 remains in solution:[8]
Mercury(II) cyanide is poison with health hazard classification 3, having an oral LD50 of 33 milligrams per kilogram in mice and a subcutaneous LD50 of 2.7 milligrams per kilogram in dogs.[14]
^ abcdAylett, B.J. "Mercury (II) Pseudohalides: Cyanide, Thiocyanate, Selenocyanate, Azide, Fulminate." Comprehensive Inorganic Chemistry 3:304-306. J.C. Bailar, Harry Julius Emeléus, Sir Ronald Nyholm, and A.F. Trotman-Dickenson, ed. Oxford: Pergamon Press, 1973; distributed by Compendium Publishers (Elmsford, NY), p. 304.
^Wong, P.T.T. J. Chem. Phys.1984, 80(12), 5937-41.
^ abF. Wagenknecht; R. Juza (1963). "Mercury (II) cyanide". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2pages=1021. NY,NY: Academic Press.
^ abcMiller, W.L. Elements of Chemistry: Organic chemistry, 5th ed. New York: John Wiley & Sons, 1880, p. 100.
^Brunton, L.T. A Text-Book Of Pharmacology, Therapeutics And Materia Medica. London: MacMillan & Co., 1885.
^Brotherton, T.K.; Lynn, J.W. Chemical Reviews1959, 59(5), 841-883, 844-846.
^Draper, Neil D.; Batchelor, Raymond J.; Sih, Bryan C.; Ye, Zuo-Guang; Leznoff, Daniel B. (2003). "Synthesis, Structure, and Properties of [(tmeda)Cu[Hg(CN)2]2][HgCl4]: A Non-Centrosymmetric 2-D Layered System that Shows Strong Optical Anisotropy". Chemistry of Materials. 15 (8): 1612–1616. doi:10.1021/cm021716r.
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