Effect of Pressure on the C–Fe Bond in Ferrocyanides and Ferricyanides

Abstract

High‐pressure studies have been made on Fe–C bonding in ferrocyanides and ferricyanides using Mössbauer resonance. For the Cu, Ni, and Zn ferrocyanides a partial conversion to high‐spin Fe(II) was observed at high pressure and elevated temperature. This is explained in terms of reduced metal‐to‐ligand back donation at high pressure. The ferricyanides reduced to ferrocyanides at modest pressure and room temperature. At high pressure and high temperatures all these salts showed extensive conversion to high‐spin Fe(II). The process was reversible, but with considerable hysteresis. In prussian blue the high‐spin Fe(III) and low‐spin Fe(II) were separately tagged with Fe⁵⁷. The high‐spin Fe(III) reduced strongly to high‐spin Fe(II). The low‐spin Fe(II) showed a partial conversion to low‐spin Fe(III) at modest pressures. This conversion was independent of temperature. At higher pressures it converted to high‐spin Fe(II) in an amount which increased sharply with temperature.