Mossbauer spectroscopic studies of thermal decomposition products in substituted pentacyanoferrate(II) and bridged binuclear complexes

Abstract

Mossbauer spectra of substituted pentacyanoferrates( ll) 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, <img src='/image/spc_char/delta.gif' border=0>E_Q = 0.73-0.99 mms ^-1 at room temperature. The isomer shift values, δ = 0.23-0.30 mms^-¹ suggest iron atoms in +2 low spin state. The complexes start decomposing at 50°C yielding residual weight (49.1-55.2%) in the temperature range 700-800°C. The Mossbauer spectra recorded after heating at 200°C exhibit an asymmetric doublet suggesting partial decomposition. At 500°C, a six line pattern starts appearing which on further heating at > 700°C turns into eight or ten lines suggesting the formation of α-Fe₂O₃of different particle sizes and iron carbide along with metal phase.