Search

The effect of pressure on the Mössbauer resonance spectra of Fe(III) with thiocyanate (M-SCN) and isothiocyanate (M-NCS) ligands has been studied. Fe(NCS)(3).6H(2)O, which has the isothiocyanate structure, reduces with increasing pressure, reversibly, and with a pressure dependence for the conversion very similar to that shown by a wide variety of ionic ferric compounds. K(3)Fe(SCN)(6) has the thiocyanate structure. At low pressures, it exhibits a significantly larger reduction than the Fe(NCS)(3). With increasing pressure the thiocyanate complexes isomerize, each complex apparently exhibiting about the same degree of conversion at a given pressure. At 150 kb the isomerization is essentially complete. The reduction of the Fe(III) to Fe(II) is reversible but the isomerization is not, and the sample, when powdered and reloaded in the high-pressure cell, exhibits the isomer shift, quadrupole splitting, and Fe(III) to Fe(II) conversion characteristic of an isothiocyanate. Heating the thiocyanate to 110 degrees C at 5 kb yields a mixture of thiocyanate and isothiocyanate that converts with pressure completely to the isothiocyanate.