Al. Barra et al., Single-molecule magnet behavior of a tetranuclear iron(III) complex. The origin of slow magnetic relaxation in iron(III) clusters, J AM CHEM S, 121(22), 1999, pp. 5302-5310
The synthesis, crystal structure, and magnetic characterization of a novel
tetranuclear iron(III) methoxo-bridged cluster of formula Fe-4(OCH3)(6)(dpm
)(6) (where Hdpm = dipivaloylmethane) is reported. The cluster has a ground
spin state of S = 5, which is selectively populated below 20 K. High-field
EPR spectra revealed that the system has a uniaxial magnetic anisotropy, c
orresponding to a zero field splitting parameter D = -0.2 cm(-1) of the S =
5. Such anisotropy below 1 K gives rise to the slow relaxation of the magn
etization similar to that of super-paramagnets. To investigate the origin o
f the magnetic anisotropy we have evaluated the projection of the single-io
n and dipolar contributions to the zfs of the ground state. The zfs tensors
of the three structurally independent iron(III) centers have been calculat
ed from the coordination geometry and spectroscopic data using the angular
overlap model. To test the reliability of the approach high-field EPR spect
ra of the parent monomer Fe(dpm)(3) have been recorded to compare the calcu
lated and experimental zfs parameters.