Synthesis of tris(N,N′-dialkyldithiocarbamato) iron(III) complexes and their thermal decomposition studies by various techniques

Several complexes of the type [Fe(S2CNR1R2)3] with symmetrical (R1 = R2 = C6H5, C6H5CH2, C4H8N and C5H10N) and unsymmetrical ligands (R1 = CH3, R2 = C6H5 and n-C4H9; R1 = C2H5, R2 = C6H5 and n-C4H9) have been prepared and characterized by elemental analysis, infrared spectroscopy and magnetic measurements. Thermogravimetric studies of the complexes exhibit a prominent weight loss of ∼70% in the temperature range 200–350 °C. In most cases decomposition occurs in two stages though in some cases it also occurs in a single, two and three stages. Thermogravimetric studies and differential thermal analysis suggest the formation of iron sulphide as an intermediate but finally Fe2O3 is formed. Room temperature Mössbauer spectra exhibit an unsymmetrical doublet resolved into two quadrupole doublets corresponding to an equilibrium mixture of high and low spin states. Mössbauer spectra recorded after heating the samples at 250, 550 and 750 °C in air confirm the formation of iron sulphide and γ-Fe2O3 in a particular case as intermediate products though finally α-Fe2O3 is formed. The activation energy for the thermal decomposition varies between 61 and 198 kJ mol−1 and it is a first order reaction. It is suggested that intramolecular rearrangement may be taking place during decomposition.