Magnetic susceptibility and magnetic anisotropy studies in some ferric dithiocarbamates exhibiting spin-crossover phenomena

Abstract

The average magnetic susceptibility and magnetic anisotropy between 77 and 300 K on three ferric dithiocarbamates, Fe[RR’(dtc)13 (R, R’ = ethyl, n-butyl, and pyrrolidyl), crystallized from benzene have been reported. The systems exhibit spin crossover between two spin states, S = and 5/2. The average susceptibility measurements, on samples crystallized from benzene or chloroform-ethanol mixture, show a strong dependence on temperature and on the solvent molecules in the lattice. The effect is most significant in the n-butyl and pyrrolidyl derivatives. Magnetic anisotropy measurements show the existence of considerable rhombic distortion in the systems, contrary to the axial symmetry deduced from x-ray structural investigations. The experimental data have been analyzed by making appropriate modifications in the theory based on thermal equilibrium between 2Tz and 6A1 terms. The effects of trigonal distortion, namely (1) the splitting of ’T2 due to trigonal distortion (6J, (2) zero-field splitting of 6A1 (D), and (3) mixing of two sets of “e” orbitals ( q ) , were considered. The ratio of vibronic partition functions for the 6Al and ’T2 terms was introduced in the form of a parameter C. The parameter C was found essential for fitting the average susceptibility data. The various ligand field parameters such as the separation of 2Tz 6A1 (&), al, D, C, and q have been estimated. The average susceptibility data are rather insensitive to the sign of the a1 and it is shown that the magnetic anisotropy data provide a means of estimating the sign and magnitude of 6,. 61 was found to be negative in all the three derivatives crystallized from benzene. This is contrary to the earlier studies, where the average magnetic susceptibilities were fitted with positive values of hl.