Mossbauer spectroscopic studies of thermal decomposition of substituted pentacyanoferrate(II) complexes

The thermal behaviour of substituted pentacyanoferrates(II) of the type Na-3[Fe(CN5)L]. xH(2)O, where L = n-, sec-, tert- or iso-butylamine, di-iso-butylamine or tri-n-butylamine, was investigated with the aid of Mossbauer spectroscopy, XRD and TG-DTG-DTA. The Mossbauer spectra of these complexes exhibit a quadrupole doublet with Delta E-Q = 0.70-0.83 mm s(-1) at room temperature. The isomer shift, delta = 0.00 +/- 0.03 mm s(-1) suggests that the iron atom is in the +2 low-spin state. The complexes start to decompose at 50 degrees C, yielding a residual mass of 5.8 -21.3% in the temperature range 900-950 degrees C. The Mossbauer spectra recorded after heating at 150 and 300 degrees C exhibit an asymmetric doublet, suggesting partial decomposition. The Mossbauer spectra at higher temperature are complex. At different stages of the thermal process, the presence of alpha-Fe2O3, gamma-Fe2O3, alpha-Fe, Fe3C and Fe3O4 was demonstrated.