Magnetic moment and Mössbauer spectral studies of spin-crossover in tris(N,N'-dialkyldithiocarbamato)iron(III) complexes and their thermal decomposition

Room temperature Mössbauer spectra of tris(N,N'-dialkyldithiocarbamato)iron(III) complexes [(R^sub 2^NCS^sub 2^)^sub 3^Fe] (R = Me, Et, n-Pr, i-Pr, n-Bu and i-Bu) exhibit an asymmetric doublet which can be resolved into two doublets, each corresponding to high and low spin states in equilibrium. The quadrupole splitting (ΔE^sub Q^), in general, increases with the molecular weight of the alkyl group in both the cases. Plots of magnetic moment (μ^sub eff^) versus temperature show that dimethyl-, diethyl-, di-n-propyl- and di-n-butyl-substituted dithiocarbamato complexes are equilibrium mixtures of high and low spin states at room temperature, but increasingly adopt low spin at the liquid nitrogen temperature. However, the di-i-propyl- and di-i-butyl-substituted dithiocarbamato complexes exhibit primarily low spin state in the 77-350 K range, with a small contribution (