The Crystal and Molecular Structure of Mercury Fulminate (Knallquecksilber)

Abstract 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.