The tetranuclear trianion [Fe4Te4(SC6H5)4]3-: crystal and molecular structure and magnetic properties

The synthesis and the spectroscopic, magnetic, and structural characterization of the compound (Et4N),[Fe4Te4(SPh),] (Ph = C6H5) are reported. The complex crystallizes in the orthorombic system, space group Fdd2, with a = 39.976 ( 5 ) A, b = 24.963 (6) A, and c = 12.200 (2) A. The molecular structure consists of discrete tetranuclear anions [Fe4Te4(SPh),13- with a cubane-like [Fe4Te4]+ unit. The magnetic behavior has been interpreted by using the Heisenberg-Dirac-Van Vleck exchange coupling model with antiferromagnetic interactions between the iron centers. The ground state has been found to correspond to a total spin state S = 3/2. EPR and 'H-NMR spectra are also reported. The available magnetic data of Fe4S4 and Fe4Se4 clusters have also been interpreted providing the correct ground state. The increased distance between the irons in the [ Fe4Te4]+ core in comparison to the analogous [Fe4S4]+ and [Fe4Se4]+ cores decreases the antiferromagnetic coupling among the iron ions. The influence of geometric parameters on the exchange pathways between iron atoms in this class of compounds is discussed within the orbital model of the exchange interaction using EHMO theory.