THE EFFECT OF PRESSURE ON THE OXIDATION STATE OF IRON, II. OXYGEN LIGANDS

Abstract

In a series of papers from this laboratory1-4 we have discussed the effect of pressure on the oxidation state of iron, on the isomer shift (s-electron density at the nucleus), and on the quadrupole splitting (splitting of the nuclear level of spin 3/2 due to interaction with an electric field gradient at the nucleus) for a variety of iron compounrds. Since high-spin ferrous ions exhibit a relatively low eleetron density at the nucleus (isomer shift 1.2-1.4 mm/sec relative to metallic iron) and large quadrupole splitting (2-43 mm/sec), whereas high-spin ferric compounds show a distinctly lower isomer shift (0.3-0.5 mm/sec) and relatively small quadrupole splitting (0.3-0.6 mm/sec), it is easy to identify one phase in the presence of the other. The observations can be summarized as follows :' (1) With increasing pressure, Fe(III) ion reduces to the Fe(II) state (reversibly) in a wide variety of compounds including halides, phosphate, sulfate, citrate, ferricyanide, ete. The conversion as a function of pressure is of the form: