MOSSBAUER SPECTROSCOPIC STUDIES OF THERMAL-DECOMPOSITION PRODUCTS IN SUBSTITUTED PENTACYANOFERRATE(II) AND BRIDGED BINUCLEAR COMPLEXES

Mossbauer spectra of substituted pentacyanoferrates(II) of the type Na3[Fe(CN)5L].xH2O where L = pyrrolidine, piperidine, 3-cyanopyridine, nicotinic acid and nicotinamide and binuclear complexes of the formulae Na6[Fe(CN)5L(CN)5Fe].xH2O where L = 4-cyanopyridine and pyrazine exhibit well resolved quadrupole doublet, DELTAE(Q) = 0.73-0.99 mms-1 at room temperature. The isomer shift values, delta = 0.23-0.30 mms-1 suggest iron atoms in + 2 low spin state. The complexes start decomposing at 50-degrees-C yielding residual weight (49.1-55.2%) in the temperature range 700-800-degrees-C. The Mossbauer spectra recorded after heating at 200-degrees-C exhibit an asymmetric doublet suggesting partial decomposition. At 500-degrees-C, a six line pattern starts appearing which on further heating at > 700-degrees-C turns into eight or ten lines suggesting the formation of alpha-Fe2O3 of different particle sizes and iron carbide along with metal phase.