Spin crossover studies in mixed ligand complexes of tris(N-ethyl, N′-n-butyldithiocarbamato)iron(III) with NN, NO and OO containing bidentate ligands and their thermal decomposition

Mixed ligand complexes of the type Fe(ebtc)2L and Fe(ebtc)L2, where ebtc=N-ethyl, N'-n-butyldithiocarbamate and L=1,10-phenanthroline (phen), 8-hydroxyquinoline (oxine) and acetylacetone (acac) have been synthesized and characterized by IR, magnetic moment and Mossbauer spectral studies. Metal-ligand vibrations corresponding to FeS, FeN and FeO were observed in the far IR region. Especially for FeS and FeN two different frequencies corresponding to high spin (HS) and low spin (LS) states were observed. Room temperature Mossbauer spectra of the complexes exhibit an asymmetric doublet resolved into two doublets corresponding to high and low spin states in equilibrium. Variable temperature magnetic moment and Mossbauer spectral studies suggest spin crossover (6A1g- > 2T2g) for [Fe(ebtc)3], [Fe(ebtc)2(phen)]+ and [Fe(ebtc)(phen)2]2+ complexes, almost no change for [Fe(ebtc)(oxine)2] complex, spin transition (4T1g- > 2T2g) in [Fe(ebtc)2(acac)] and [Fe(ebtc)(acac)2] complexes and high spin to intermediate spin (6A1g- > 4T1g) state in [Fe(ebtc)2(oxine)] complex. Thermogravimetric studies suggest that all the complexes are stable up to 200 deg C and decomposition occurs in two or three stages finally yielding Fe2O3 in most cases though two of the complexes seem to be volatile.