H4(CN)6Fe

from The Collaborative International Dictionary of English v.0.48

Ferrocyanic \Fer`ro*cy*an"ic\, a. [Ferro- + cyanic: cf. F.
   ferrocyanique.] (Chem.)
   Pertaining to, derived from, or designating, a ferrocyanide.
   [1913 Webster]

   {ferrocyanic acid} (Chem.), a white crystalline substance,
      {H4(CN)6Fe}, of strong acid properties, obtained from
      potassium ferrocyanide, and regarded as the type of the
      ferrocyanides; -- called also {hydro-ferrocyanic acid},
      {hydrogen ferrocyanide}. etc.
      [1913 Webster]