Synthesis and Crystal Structure of a New Orthorhombic Polytype of Potassium Ferricyanide

A new four-layer orthorhombic polytype of potassium ferricyanide, K3Fe(CN)(6), has been determined by single-crystal X-ray diffraction supported by powder X-ray diffraction measurements. It crystallizes in the space group Pbcn with lattice parameters a = 10.3922(7) angstrom, b = 8.3508(5) angstrom, c = 26.838(2) angstrom and Z = 8, indicating a doubled orthorhombic cell along the c direction compared with the previously reported two-layer orthorhombic polymorph. The structural relationship between these two forms is then discussed with the support of DFT calculations.