The Crystal and Molecular Structure of Mercury Fulminate (Knallquecksilber)

A short survey on the fascinating history of mercury fulminate is given. The crystal structure of Hg(CNO)2 has been determined using single crystal X‐ray diffraction. Mercury fulminate crystallizes in an orthorhombic cell, space group Cmce with a = 5.3549(2), b = 10.4585(5), c = 7.5579(4) Å and Z = 4. The distances and angles in the O‐N≡C‐Hg‐C≡N‐O molecule are Hg‐C 2.029(6) Å, C≡N 1.143(8) Å, N‐O 1.248(6) Å and C‐Hg‐C 180.0(1)°, Hg‐C≡N 169.1(5)°, C≡N‐O 179.7(6)°. Each mercury atom is surrounded by two oxygen atoms from neighbouring Hg(CNO)2 molecules with a nonbonding distance of Hg···O 2.833(4) Å. The Hg‐C bond lengths in the linear Hg(CNO)2 molecules are shorter than those in the tetrahedral complex [Hg(CNO)4]2−. This refers to a large contribution of the 6s orbital in the Hg‐C bonds of Hg(CNO)2. The results of the X‐ray powder investigation on Hg(CNO)2 are also reported.