High-pressure studies of the micro-Raman spectra of iron cyanide complexes: Prussian blue (Fe_4[Fe(CN)_6]_3), potassium ferricyanide (K_3[Fe(CN)_6]), and sodium nitroprusside (Na_2[Fe(CN)_5(NO)]·2H_2O)

摘要

The pressure dependences of the peaks observed in the micro-Raman spectra of Prussian blue (Fe_4[Fe(CN)_6]_3), potassium ferricyanide (K_3[Fe(CN)_6]), and sodium nitroprusside (Na_2[Fe(CN)_5(NO)]·2H_2O) have been measured up to 5.0 GPa. The vibrational modes of Prussian blue appearing at 201 and 365 cm~(-1) show negative dη/dP values and Grüneisen parameters and are assigned to the transverse bending modes of the Fe-C-N-Fe linkage which can contribute to a negative thermal expansion behavior. A phase transition occurring between 2.0 and 2.8 GPa in potassium ferricyanide is shown by changes in the spectral region 150-700 cm~(-1). In the spectra of the nitroprusside ion, there are strong interactions between the FeN stretching mode and the FeNO bending and the axial CN stretching modes. The pressure dependence of the NO stretching vibration is positive, 5.6 cm~(-1) GPa~(-1), in contrast to the negative behavior in the iron(II)-meso-tetraphenyl porphyrinate complex.